Radio control racer needs an electrical mentor
Radio control racer needs an electrical mentor
(OP)
Hello,
Hey I get the first post!!!!
I race high speed RC cars, nitro for the most part. A racing buddy and I decided to go after the overall record, 161 mph set with a brushless motor and Lipo cells in 2008.
I have built the car (below) but my 'buddy', who had the electrical knowledge, decided to go off on his own. It has taken a year to get the car sorted out so it runs straight and stays on the ground (not that easy to do). I'm to the point that I'm starting to put power to the ground (hit 130 last weekend) and I have data from the speed control (watts, amps, rpm, voltage, etc.) but I don't know what to do with the info.
The ultimate goal is to be the first to 200 mph.
I could really use some help interpreting the data to tell me which way to go as well as making sure I'm not making other wiring errors (I'm sure I am!) Once I get the jist of what does what does what I should be okay and you'll be off the hook unless you want to stay involved.
Thanks in advance,
Gary
Hey I get the first post!!!!
I race high speed RC cars, nitro for the most part. A racing buddy and I decided to go after the overall record, 161 mph set with a brushless motor and Lipo cells in 2008.
I have built the car (below) but my 'buddy', who had the electrical knowledge, decided to go off on his own. It has taken a year to get the car sorted out so it runs straight and stays on the ground (not that easy to do). I'm to the point that I'm starting to put power to the ground (hit 130 last weekend) and I have data from the speed control (watts, amps, rpm, voltage, etc.) but I don't know what to do with the info.
The ultimate goal is to be the first to 200 mph.
I could really use some help interpreting the data to tell me which way to go as well as making sure I'm not making other wiring errors (I'm sure I am!) Once I get the jist of what does what does what I should be okay and you'll be off the hook unless you want to stay involved.
Thanks in advance,
Gary





RE: Radio control racer needs an electrical mentor
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Radio control racer needs an electrical mentor
First question: Is any of your motor or battery wiring, e.g. intercell connectors, smaller than the 8 gage wire that the controller uses? I.e., did you follow the comprehensive instructions in the controller users manual? What did you do differently?
Second question: What's your gearing like? I'm assuming (correct me if I'm wrong) that you're using a brushless motor, in which case the speed of the vehicle is controlled by the maximum frequency applied by the motor controller, the gearing between the motor and the tires, the tire diameter, the growth in tire diameter with speed, and slip between the tire and the ground. If you're already reaching the controller's maximum rpm speed, then you need to change the gearing or the tires, a lot, in order to reach your goal.
Third question: What data? Post it and we'll take a look. If you're concerned about discussing it publicly, I'm not that hard to find. Look on LinkedIn.
Mike Halloran
Pembroke Pines, FL, USA
RE: Radio control racer needs an electrical mentor
*Is any of your motor or battery wiring, e.g. intercell connectors, smaller than the 8 gage wire that the controller uses?
- The front 4s pack has 8ga wire but the rest, I believe is 10ga. I tried to get 8ga wires for the rear 2s packs but the battery supllier would only put 10ga on them. The motor leads are 10 ga. Another question, what effect does the length of the wires have? I've been told to keep the wires between the batteries and the esc as short as possible which I have but I have a fairly long (8 inch) 10ga wire connecting the front and rear packs.
*did you follow the comprehensive instructions in the controller users manual?
- They're not all that comprehensive....they just show the basic wiring diagram and arming instructions
*What did you do differently?
- With the exception of trying to go REALLY fast, nothing.
*What's your gearing like?
- The chassis gearing is 1.66:1. The tires are rotating @ 14400 rpm @ 100mph
*I'm assuming (correct me if I'm wrong You're correct) that you're using a brushless motor, in which case the speed of the vehicle is controlled by the maximum frequency applied by the motor controller,...
- These are MY assumptions and correct me if I'm wrong...The esc(electronic speed control) is built for up to 32 volts, which is what I'm putting into it. The motor is 2200kv which, at 32 volts, would rev at 70,400 rpm (but the motor has a 60,000 rpm limit). ASSUMING an 80% efficiency it would top out at 56,000. With the gearing and tire diameter of the car it should hit 180mph @ 43,000 rpm. That gives me 13,000 rpm to give up to aero and parasitic drag. My first goal is the record, then I can play with gearing for 200.
...the growth in tire diameter with speed,...
- There is very little tire growth. Growth is bad because centrifugal(?) force literally tears the foam apart. I turn the tires down so the foam is only about 1/8 - 3/32 of an inch thick, thereby reducing the mass that's trying to tear itself apart. I have spin tested these tires to 25,000 rpm on my router with no issues.
...and slip between the tire and the ground.
- Once the car is moving the shape of the nose and the rear wing put down force on the tires. I have a speedometer that I'm going to install on the rear axle so I can see if the tire speed is significantly different from the timed speed. My feeling is that they're not. During my last run the data showed a 281 amp draw...my intuition tells me that the tires were firmly planted. If they were spinning the amp draw would have been less...yes?
*If you're already reaching the controller's maximum rpm speed, then you need to change the gearing or the tires, a lot, in order to reach your goal.
- I don't believe I'm reaching the rpm limit but do appear to be reaching the maximum amperage limit since it shut down part way through a run. The limit had been set at 250A... I have bumped it up to 275 and have the 300 setting in reserve. Even at that amperage draw the temp of the esc was only 110 degrees. Because the car is driving so well and 'stuck' I have been punching the throttle sooner... I'm thinking that a slower application will keep the amperage draw down and allow a complete run.
*What data? Post it and we'll take a look.
- The esc spits out rpm, ripple, amperage, voltage, temperature, throttle position, time to full throttle and more.... I'll be running this weekend and will post it up. I don't believe my data will do anything for anyone else but me since the few cars trying for this target are so vastly different in weight, size and drive wheels.
I have attached a pic of the other side of the car...the center black gear is on the motor shaft while the other two gears are jack shafts... the rear has a pulley with a belt that runs between the two 2s packs and the front shaft has a pulley and belt visible in the previous photo driving the front wheel. In the configuration shown here, with 6s (24 volts) and a 1500kv motor the car ran through the taps at 116 mph....assuming 80% efficiency, the calculations work out to 120 mph....pretty darned close to reality!
I deeply appreciate your offer to help, Mike....
Gary O
RE: Radio control racer needs an electrical mentor
re. ESC, is 32V the maximum supply voltage rating?
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RE: Radio control racer needs an electrical mentor
Mike Halloran
Pembroke Pines, FL, USA
RE: Radio control racer needs an electrical mentor
Gary, the 10 gage (vs 8 gage) wire is hurting more than an extra inch of length.
An online calculator says that for copper wire the resistance per 10 feet is
10 milli-ohms for 10 gage wire, and
6 milli-ohms for 8 gage wire, and
4 milli-ohms for 6 gage wire.
Single milli-ohms start making a big difference at a couple hundred amperes.
It might be a worthwhile exercise to map your wiring by length and gage,
put it in a spreadsheet, and compute the resistance and voltage drop at 250A for the whole circuit.
Does anybody use busbars as chassis elements? Just a thought...
Mike Halloran
Pembroke Pines, FL, USA
RE: Radio control racer needs an electrical mentor
Voltage drop calculations based on 250 Amps and the DC resistance of the wire show 0.25 Volts per foot for #10 AWG wire and 0.15 Volts per foot for #8 AWG wire.
But; The heating loss in a foot of wire at 250 Amps is 62 Watts for #10 wire and 37.5 Watts for #8 Wire.
Also, you will be running at at least 400 Hz at 100 mph and skin effect will be increasing both the voltage drop and the Watts loss.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Radio control racer needs an electrical mentor
All the more reason for fatter and shorter wires. Additionally, since the wires are likely to get warm from all the current, getting them cooled with lots of air flow might help, but that's a trade vs. even fatter wires than you might otherwise need.
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RE: Radio control racer needs an electrical mentor
IRStuff, yes my packs are 150c discharge which is the max on the market. Although the photos show standard plug type connectors to the batteries, they've all been changed over to gold 'bullet' connectors. I can certainly shorten several of the wires and will do so. The esc's maximum rating is '8s' which would be 32V. Whether or not it would live at a higher voltage I may have to find out when the time comes that I need more voltage! Here's a link....
http://www.castlecreations.com/products/mamba_xl2....
Mike, yes the motor rating is rpm per volt. The motor I'm currently using is a Castle 1515... their site has limited data http://www.castlecreations.com/products/neu-castle... . Once I have this motor topped out I'll switch to a Neu motor which is the standard of the hobby http://www.neumotors.com/Site/1500_series.html . I like your idea of mapping the wires...I'll do a before and after calc.
Busbar as a chassis element? Hmmmm...let me think on that one.
Bill, I researched 'skin effect' (what a crazy concept!)... since it is an AC factor that would only effect the wires between the esc and motor, correct?. Not much I can do there...their as short as they can be and the wires can't be changed. The next car iteration could resolve that with a relocated esc.
One thing that may come into play is that full power is applied for about 5-7 seconds with the throttle being 'rolled' on prior to that. Also I will be drilling out the aluminum pieces and replacing the fiberglass parts of the car with 'swiss cheesed' carbom fiber plates to lower the weight.
Thanks so much for the thoughts...I have work to do now!
Gary
RE: Radio control racer needs an electrical mentor
See? This is the kind of stuff I wouldn't think was important and looking at one of my rival's cars he doesn't either. However, by 'buddy's' wires are as short as possible....
RE: Radio control racer needs an electrical mentor
Mike Halloran
Pembroke Pines, FL, USA
RE: Radio control racer needs an electrical mentor
I flipped the motor and shortened the wires, ending up with 10 inches less 10ga and as a side benefit took seven ounces out of the car. Double bonus! Here's the before and after....
RE: Radio control racer needs an electrical mentor
I'll be running the car Sunday at my local test site, an industrial road with no traffic, straight, long and smooth which will give me about 600 feet of run up before going by the radar gun. I should have a bunch of data to share after that. I'll be most interested to see if there was a significant amperage draw drop and voltage increase.
RE: Radio control racer needs an electrical mentor
A million years ago (1970s), we were playing around with the toy RC cars sold by Radio Shack. There was a fairly large "Porsche" that used something like 6 alkaline D-cells for motor supply. I added another batch (4?, 6?) of D-cells to the roof and wired them in series using wires and the clever trick of a piece of double-sided PCB to insert between two of the existing cells. This rather mindless concept worked extremely well and the toy RC car was much more powerful than originally designed.
PS: at the currents you're running, beware the possibility of magnetic (DC) or EMI (AC components) effects. If you see mysterious malfunctions of the electronics then consider EMI as one possibility. Keeping the supply and return paths close together can help self-cancel the emissions.
RE: Radio control racer needs an electrical mentor
The electronics are light years ahead of what they were just five years ago. We can get about 3/8 of a mile range from our radios and now the problem is these old eyes! Electronic 'funny stuff' isn't all that common anymore....but if I do, that'll be the first thing to look at!
Thanks!
Gary
RE: Radio control racer needs an electrical mentor
RE: Radio control racer needs an electrical mentor
That's why I'm here..... Like the wire post above, once the concept was given to me I could understand it. Things like that 'skin effect'? Never heard of it. You guys have given me more guidance than I could hope for.
I do have a question.... If my car were to suddenly break traction and the motor start to spin up, my electrical 'buddy' said there would be a big spike up in the amperage..... that doesn't make sense to me. It would seem that the tires breaking loose would cause a decrease in the amperage since the motor wouldn't be pulling as hard as it would with good traction. Yes? No? If I were to punch it at a standing start the amps would go way up, wouldn't they?
Thanks!
RE: Radio control racer needs an electrical mentor
If the controller were commanding constant speed and the load went away, the current should go down.
If the controller were commanding acceleration and the tires broke traction, the motor would now be accelerating only itself, the gears and the wheels, the controller might immediately go to its programmed current limit. ... or not; I don't know that much about BLDC motor controls in general, and nothing about this one in particular.
In particular, I don't see an encoder on the motor, so the controller must be sensing shaft rpm indirectly, or maybe not at all.
I'm on my second energy saving variable speed air conditioner. They don't have encoders on their three phase motor either, but they manage to sense the load on the air handler fan somehow anyway. I've read one of the patents, and I still don't understand it.
Mike Halloran
Pembroke Pines, FL, USA
RE: Radio control racer needs an electrical mentor
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RE: Radio control racer needs an electrical mentor
A voltage spike is more to be expected.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Radio control racer needs an electrical mentor
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RE: Radio control racer needs an electrical mentor
There are two types of brushless motors used in RC racing, sensored and unsensored. The motor in my car is the unsensored type. Sensored motors(mostly made by NOVAK) have a harness going between the end of the motor and the speed control. I can only assume that's what the encoder would be.
RE: Radio control racer needs an electrical mentor
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RE: Radio control racer needs an electrical mentor
Maui
www.EngineeringMetallurgy.com
RE: Radio control racer needs an electrical mentor
Size is also a consideration and the one I have in there is about the biggest I can fit (was lucky to squeeze that one in)
Gary O
RE: Radio control racer needs an electrical mentor
Maui
www.EngineeringMetallurgy.com
RE: Radio control racer needs an electrical mentor
Do you think the XL2 would take a couple more cells? one more?
RE: Radio control racer needs an electrical mentor
Rather than using a radar gun you might want to consider a photogate timer.
RE: Radio control racer needs an electrical mentor
I use a radar gun for testing but at our speed meets we use dual infrared optical timers which have to be within 3% of each other to be an official record. They are amazingly accurate and consistent usually being within 1%.
RE: Radio control racer needs an electrical mentor
As long as the plane is able to get me back to beautiful Cali-for-ny-ay I'll run it Sunday and get some data from the esc to see where it's at now. Anxious to see the difference with shorter wires and a pound lighter.
RE: Radio control racer needs an electrical mentor
The amperage draw was quite a bit lower with a max of 211 amps vs 281 on a previous run. The esc never shutdown and didn't really get hot (113 degrees)
The only down side is that the car hit a bump...I got out of the 'groove' but didn't let up...and it made a slight right turn into the curb and tumbled to a stop....and it took a looooooong time to stop! Unfortunately my radar gun didn't work and the little speedometer I had in the car got pretty banged up. Also the main switch got turned off during the tumble erasing any speed saved. The only damage is the fin sheared off but it's just the aluminum brackets that were damaged.
Some of the other available data....
Voltage ranged from a high of 32.8(static) to 26.9 (a downward spike under load)
Maximum watts was 5800 and the line on the graph pretty much paralleled the amperage.
Ripple had a max of 4.96....what is that? It again mimiced the amperage but then dropped way off as the rpm climbed.
There was also a percentage power out of 85% which again lsee closely followed the amperage line.
Anything wierd here? Despite the clumsy stop, I'm very happy with the reults. Next time I'm at the airstrip it's new record time!!!!!
Thank you all!
RE: Radio control racer needs an electrical mentor
We'll be waiting for the new record.
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Radio control racer needs an electrical mentor
That said, let me play armchair general and bounce ideas at you. You are totally free to disregard these, as they are entirely off the cuff.
Consider an airplane ESC and a secondary means to stop (parachute? servo actuated brake?) I think you need to throw a lot more voltage at the problem as it would give you much more headroom regarding heating, wire gauge, etc.
I'm not sure that Bonneville streamliners are the right analog for this scale. Given a 1/4 mile to accelerate, you need a constant 1G acceleration to trap @ 200mph. This is more of an acceleration problem than a sustained top speed problem. Top fuel might be better design inspiration?
I'm not positive that weight/mass is your enemy. At low speed, I'd expect with this much power you are limited by traction. Traction is roughly Mass*g, and at low speeds it is fighting against Mass*a. The M's roughly cancel because I don't suspect these tiny tires loose much grip due to increased load.
At high speed traction is roughly Mass*g + aero_downforce. And it is fighting aero_drag. In this situation the added mass may actually help (since acceleration is tapering off, the Mass*a term becomes small). In addition any additional inertia might help dampen things out.
While I'm not suggesting you intentionally add mass, if there are places where you can benefit from a heavier component or stiffer structure, it might be a worthwhile swap.
Thought about active-aero? IE: Steer with a rudder? Or trim tabs controlled via heading-hold gyro? You are effectively building a ground-based airplane here...
Maybe an on-board microcontroller to automate your throttle-ramp via some kind of feedback (like accelerometer data?). This way, the "driver" could just "punch it!" and the onbourd MCU could execute an elaborate acceleration profile.
Did the Team Associated car ever make 200? Their website is kinda dead.
RE: Radio control racer needs an electrical mentor
Maui
www.EngineeringMetallurgy.com
RE: Radio control racer needs an electrical mentor
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RE: Radio control racer needs an electrical mentor
Maui
www.EngineeringMetallurgy.com
RE: Radio control racer needs an electrical mentor
I'm always open to ideas....anyone who thinks he's solved ALL the problems hasn't really tried to do anything of merit.
That said, let me play armchair general and bounce ideas at you. You are totally free to disregard these, as they are entirely off the cuff.
*I do my best thinking at bizarre times....nothing is too far out of the box.
Consider an airplane ESC and a secondary means to stop (parachute? servo actuated brake?) I think you need to throw a lot more voltage at the problem as it would give you much more headroom regarding heating, wire gauge, etc.
This past weekend I came across a three mile long, freshly paved stretch of road that is free of bumps, cracks, reflectors, manholes, houses and any other defects normally found in a road so braking becomes less of an issue. So far heat hasn't been an issue either....the motor is warm and the esc is only 115 degrees. The rpm graph on my 149 mph run showed a fairly straight line with no signs of flattening out so I think I'm still in the power band and only need another 15 mph for the record. For 200 I'm definitely going to have to look at more voltage. At that point an airplane ESC would be needed...do they have any with 200 amp capacity? I’ll have to check that out.
I'm not sure that Bonneville streamliners are the right analog for this scale. Given a 1/4 mile to accelerate, you need a constant 1G acceleration to trap @ 200mph. This is more of an acceleration problem than a sustained top speed problem. Top fuel might be better design inspiration?
*The guy who was going to be doing the electrical part of this project has gone with a dragster for his attempt. I see two problems, the first being only two wheel drive. It's my feeling that no wheel should touch the ground unless it's helping to move the car. He has been struggling to put his power to the ground since 30% of his weight ( I would guess) is just holding the front of the car down. He is putting a fairly aggressive rear wing on the car to counteract this problem. The second is the center of gravity in relation to the center of pressure.... when he has gotten sideways the car just starts to spin with the front end visibly being blown to the rear.
I'm not positive that weight/mass is your enemy. At low speed, I'd expect with this much power you are limited by traction. Traction is roughly Mass*g, and at low speeds it is fighting against Mass*a. The M's roughly cancel because I don't suspect these tiny tires loose much grip due to increased load.
With all wheel drive and about a six pound weight I am able to put full power to it fairly early. My earlier design(with much narrower rear tires) could spin them easily.
At high speed traction is roughly Mass*g + aero_downforce. And it is fighting aero_drag. In this situation the added mass may actually help (since acceleration is tapering off, the Mass*a term becomes small). In addition any additional inertia might help dampen things out.
While I'm not suggesting you intentionally add mass, if there are places where you can benefit from a heavier component or stiffer structure, it might be a worthwhile swap.
*The 'weight needed for acceleration' vs the 'weight restricting acceleration' balance is the holy grail obviously. Since I can apply full power somewhat quickly (within a couple hundred feet) I'm thinking I could stand to lose a few more ounces...I could always add some if it was too light. The overall restriction is these old eyes ability to see the dad gummed car a quarter mile away. we have a ladder in the bed of a truck which helps tremendously but to get to 200 we need as much run up and as much acceleration as possible.
Thought about active-aero? IE: Steer with a rudder? Or trim tabs controlled via heading-hold gyro? You are effectively building a ground-based airplane here...
You and I think a lot alike. The first version of this car was rudder steered...and it crashed every run. My goal was to make the nose as narrow as possible for less aero drag and didn't think I could fit steering in as well. At slow speed it had no steering and at high speed any input would roll the car. I have posted a pic below. An airplane has the air from the prop to move the tail at low speeds and it doesn't have the tires resisting every change in direction. After the 20th+/- crash I came up with the existing steering system and have no steering related crashes. Another issue that came up with the rudder is that the chassis has to roll perfectly straight with no steering input. With front wheel steering I can adjust the trim and get it rolling straight. While typing this I realized that the front end doesn’t respond well at high speed so maybe a small rudder AND front wheel steering would assist at high speeds.
Maybe an on-board microcontroller to automate your throttle-ramp via some kind of feedback (like accelerometer data?). This way, the "driver" could just "punch it!" and the onbourd MCU could execute an elaborate acceleration profile.
I have a 'delay box' used to slow the landing gear doors on airplanes and combined with a modified acceleration curve in the ESC I could do that but since adding the wider rear tires it hasn't been necessary. I just roll on the throttle and its on its way!
Did the Team Associated car ever make 200? Their website is kinda dead.
Associated was sponsoring the guy (Nic Case) who holds the present speed record to be the first to 200. First off, no....no one has been anywhere near 200 yet. Associated's plan was to go with a shaft drive car rather than belt drive. I used to run shaft drive cars until I had a shaft bend and spin itself right out of the car at about 120, taking several components with it. The differentials have a 2.5:1 reduction so for the tires to be spinning at about 28,000 rpm (200 mph) the shaft would have to be spinning at 70,000 rpm, assuming no tire slippage. After spending an 'alleged' $50,000 on the project it died on the vine. Nic is presently building a 4wd belt car for his own 200 attempt. Rumor has it he has apparently been in the mid 170's but the car blows over each time.
IMHO, the above car is too wide, increasing drag and introducing more top surface to the whims of the wind trying to pick it up. The down force needed to keep it on the ground will also keep it from 200
The 2wd dragster will need too much down force to put all that power to the ground with only 60-70% of the mass on the tires.
I have confidence in my design and will be looking for the little things, like your suggestions and other on this thread, to get it to 200.....
Thanks!
RE: Radio control racer needs an electrical mentor
I presently have a 27 volt rated 2200 kv (rpm per volt) motor on 32 volts with a 1.66 ratio to the wheels.
If I were to replace that motor with a 1650 kv 36 volt motor (same model and size motor) on 32 volts with a 1.24 ratio to end up with the same wheel speed as above will I have more or less power at the wheels?. What are the advantages or disadvantages to this new set up?
Several of you have suggested higher voltage but I have not been able to find an esc that will take more than 8s at anywhere near the amperage I’m pulling. Any other suggestions or product examples?
Thanks!
RE: Radio control racer needs an electrical mentor
RE: Radio control racer needs an electrical mentor
Is supposed to be good for 12S @ 160A. Kind of pricey though, and you are left with the problem of stopping with an airplane ESC.
If you're feeling ambitious, maybe time to use a smaller ESC to drive your own IGBT amplifier. How you handle commutation is a bit tricky there, though.
It's difficult to compare motors based only on the silly hobbyist KV ratings. It only gives you a no-load RPM @ voltage. I would *expect* the lower KV motor to have more winds, and to draw less current at the same voltage (with rotor stalled). Thus you could potentially throw more voltage at it.
RE: Radio control racer needs an electrical mentor
There is more info on the motors on the Neu site... I just used the Kv since that's what I understand.... here is a link to the page, I'm using 1515 motors because of their length.
http://www.neumotors.com/Site/1500_series.html
RE: Radio control racer needs an electrical mentor
The basic gist of it: at the same input voltage, the lower Kv motor will have a bit less power, at less rpm, and at less current draw. Upping the input voltage until the current draws are comparable results in better performance from the lower Kv motor, but now your ESC needs to handle that higher voltage.
RE: Radio control racer needs an electrical mentor
I feel like I'm on the right track with the voltage available to me, depending on how brave I want to get running the motors at higher voltages than they're rated for. It's only money!
Gary O
RE: Radio control racer needs an electrical mentor
I've never thrown voltage at one of these motors until it failed. Get yourself a cheaper one and see what the actual failure mechanism is (take pictures). I would suspect the magnets could be damaged by overheat, or the coil windings may just burn up from excess current.
RE: Radio control racer needs an electrical mentor
I can pick up Castle motors 'relatively' cheap ($100+/-) and since the present motor isn't overheating I was going to step up the kv and give it a try. You can't go after world records and worry about a few bucks. If it was easy, everybody'd be doing it!
Thanks!
RE: Radio control racer needs an electrical mentor
RE: Radio control racer needs an electrical mentor
The motors you are using work the same as a brushed DC motor (Mabuchi, etc), except the commutation is handled electronically, instead of mechanically via comm/brushes. They are usually powered by DC (batteries), but the controller generates the AC synchronous bit. So in some sense, you could call it either.
On the gearing thing: on paper it's a "maximize area under the curve" problem. In reality it gets more convoluted because the power requirements during your run can vary, and you need to watch the current draw and temperatures. You could "try it and see" and hope you can make sense of why things improved or did not. Or cobble together a basic model of your system and attempt to feed data into it to refine it until you can predict what your changes should do.
I've never been down your path, so with any luck I am not leading you entirely astray.
RE: Radio control racer needs an electrical mentor
According to a friend with 'friends in high places' at Castle they're not making 10-12s airplane/heli esc's anymore so my voltage is limited to 32 for now. I really think that'll be enough to do the job. If not I'll revisit the esc facet of this adventure.
Thanks!
Gary O
RE: Radio control racer needs an electrical mentor
I picked up a Neu 2700kv motor and a couple pulley combos so I can adjust my way into that sweet spot rpm range.
The best news is that a friend has managed to get permission to run on a beautiful airstrip about an hour and a half from my house. It's 3000 feet long and 75 feet wide......PERFECT!!!!!!
On March 30th I'll be running on our usual track site in Shafter, CA. Its about 2000 feet long but only 30 feet wide and somewhat oddly shaped. It'll be the first time at this site since I started getting suggestions from you guys. I feel very confident the car will live up to it's potential.
I wasn't able to get permission to use the nice long road I found....the airstrip is better anyway.
imcjoek, while running my car on the street I have noticed that I'm lacking sufficient steering input under acceleration and have put a small rudder back on the car to help with that.... maybe the combination of steering methods will give it the stability needed for these speeds.
BTW, one of my competitors bumped the record up to 169.19 a week ago. I felt his car was too wide and had too much down force to reach 200 and fortunately it was....gives me a little breathing room. Here's a video of his runs.....
https://www.youtube.com/watch?v=SLd53jU81as
RE: Radio control racer needs an electrical mentor
I believe imcjoek was referring to not just using a steering fin but using a gyro with the fin. Basically, the gyro would automatically adjust the fin to keep the car going straight.
I believe there are 2 types of gyro controls. One that tries to keep it going the same direction no matter what (heading holding) and one that adjusts for any change in direction not called for by the radio.
The heading holding gyros are often used in RC planes during takeoff and landing to keep the plane going straight down the runway.
So, I'm thinking run a gyro on the steering. Drive long enough to know the car is heading true down the runway and then turn on the heading holding and not steer any more.
If it is required then add a steering fin that works with the steering wheel. I'd investigate putting it towards the front so it assists the steering wheel. At any rate, you'll have to play with fin vs wheel turning to find some stable workable ratio.
RE: Radio control racer needs an electrical mentor
Did a bit of searching and voila! What a piece of wonderfulness! This allows me to start the car at a distance beyond my ability to see it! That is a must have! Thanks for the great tip....
Rudder-wise, I reinstalled it in it's original position (rear) mainly because I already had most of the parts made and it pretty much bolted back in. If it's not effective I'll investigate mounting it up front.
Gary O
RE: Radio control racer needs an electrical mentor
Heading hold gyros can still drift over time, because they use numerical integration methods to obtain the angle. Still probably better than a squishy human can do at these speeds, though.
There are also Inertial Measurement boards which combine gyro/accel/magnetometers/and sometimes GPS. They're usually used in UAV's and quadcopters, but you could probably tweak the software to give you rock solid steering.
RE: Radio control racer needs an electrical mentor
RE: Radio control racer needs an electrical mentor
I got my heading hold gyro yesterday....that's going in next to see how it works in a car. I've gotten opinions both ways.
Our next run is April 20th near Bakersfield. It's a 2000+/- foot strip about 30 feet wide. Once I get the timing lights back (assuming the car comes back in one piece!...not guaranteed) I'll make arrangement to go to the 3000 foot long 80 foot wide airstrip we got permission to use to continue the quest for 200.
To say I have high expectations is putting it lightly
RE: Radio control racer needs an electrical mentor
RE: Radio control racer needs an electrical mentor
The batteries I was running were 4s 'hand me downs' that had crashed at 170 and were seemingly getting confused and a pair of 2s packs with 10ga wire. Now I have fresh cells with monster wires!
April 20th is the meet at Minter Field near Shafter, CA. Wish me luck!!!!!!
RE: Radio control racer needs an electrical mentor
Ran at Shafter last Saturday and had a long, wide airstrip to run on. The car had more radio range than I had sight range. When the car hit about 125 it started porpoising, the rear wing pushing down hard enough to raise the front wheels. When the rear fin hit the ground and picked the rear wheels up, the front came back down and did it over and over again.
This banging broke a wire connector in the reciver pack and I lost radio control just before the traps. The car strayed off the pavement into the gravel and came to a stop in the sage brush. Wasn't any real damage, just real dusty. Also while changing the motors out I must not have tightened the pinion down enough because it departed somewhere along the way.
Here's a vodeo of the run. Although you can't see the up and down motion (I could) you can hear it. There's a puff of dust in the distance at the finish when it come to a stop.
http://www.youtube.com/watch?v=_lUYzMyl3BI
Next run/pull of the lever is May 18th. I have cut the rear wing down, made a new pinion and have rebuilt the reciever pack.
RE: Radio control racer needs an electrical mentor
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RE: Radio control racer needs an electrical mentor
Part of the idea of the wing in the back was to tansfer some of the weight to the rear. The front tire was getting chewed up quickly without the elevator but after the wear was more even with the rears. It's just another adjustment to be made.
RE: Radio control racer needs an electrical mentor
http://www.youtube.com/watch?v=mF6Tc1RxINQ
RE: Radio control racer needs an electrical mentor
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RE: Radio control racer needs an electrical mentor
www.EngineeringMetallurgy.com
RE: Radio control racer needs an electrical mentor
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RE: Radio control racer needs an electrical mentor
I have secured permission to run at the Willits airport, tentatively Aug 25th. I will post all results here.
Gary O
RE: Radio control racer needs an electrical mentor
Thought this was all set!
RE: Radio control racer needs an electrical mentor
Mike Caruso
Chicago, IL
RE: Radio control racer needs an electrical mentor
Select either of his other videos, click on his username. That brings up the other vids he's posted.
Jay Maechtlen
http://www.laserpubs.com/techcomm
RE: Radio control racer needs an electrical mentor
RE: Radio control racer needs an electrical mentor
The tail was busted, fin/elevator was missing along with some other damage but the 'core' of the car was intact. I rebuilt again and returned, this time setting the failsafe... to no avail as the car just took off after being set on the ground. It smashed into a rock damaging many of the pieces I had just repaired without making a single run.
Rebuild for the umpteenth time, fortunate that the core had again survived. Traveled down to Shafter airport (near Bakersfield) and ran 146 through the timers only to have the pinion come off so I had no brakes..... it rolls a looooooooong way at that speed and did a few endos at the end of the strip. At least there was no cliff!
Rebuild for the umpteen and one-th time and ran at Shafter again this past weekend. Actually got three runs in, all around 140 - 150 mph but wore out a front tire each time....except the first when the front blew up. Data from the speed control shows an rpm peak that calcs out to 190 mph so the tires are spinning madly. When I came home I threw aero to the wind (pun) and mounted two full size tires on the front. The weather cleared long enough for a quick test and the difference is amazing...it will accelerate to 100 in just a couple hundred feet. I underestimated the power of that motor by a bunch and will be returning to Shafter a few weeks from now to run it with those tires and see what the results are. Here's a comparison of the original single tire and the new set up... five times the rubber on the road.
If it works as well as it seems I can redesign the front half and narrow it up by an inch and a half and still retain the full width tires.
RE: Radio control racer needs an electrical mentor
Thanks,
Gary O
RE: Radio control racer needs an electrical mentor
Always optimistic!
RE: Radio control racer needs an electrical mentor
That will give you a good measure of tire growth at speed.
Mike Halloran
Pembroke Pines, FL, USA
RE: Radio control racer needs an electrical mentor
RE: Radio control racer needs an electrical mentor
http://www.autoweek.com/article/20120409/carnews01...
http://www.speedtalk.com/forum/viewtopic.php?p=406...
The point is, they're not the same diameter at speed.
Mike Halloran
Pembroke Pines, FL, USA
RE: Radio control racer needs an electrical mentor
RE: Radio control racer needs an electrical mentor
The bad thing is it was in the 150's.....
When the car comes off the track all the components are warm, but they're not really hot. VE1BILL posted earlier that "If cooling isn't your main problem, then you're not trying hard enough." It sounds like I need to up the gearing and start getting things hot. If that doesn't get me to my goal I'm going to have to start looking for a speed control and motor that can handle 12 cells, the max I can fit in the car. (I'm at 8 right now)
I have in-car video which I'll post when it downloads.
RE: Radio control racer needs an electrical mentor
Maui
www.EngineeringMetallurgy.com
RE: Radio control racer needs an electrical mentor
I'll see what changes the gearing makes on the apmperage.
Thanks!
RE: Radio control racer needs an electrical mentor
www.EngineeringMetallurgy.com
RE: Radio control racer needs an electrical mentor
Here's a video from Sunday. Actual run starts at 1:40
http://www.youtube.com/watch?v=ByMbkpyntiI
RE: Radio control racer needs an electrical mentor
http://www.electronicproducts.com/Electromechanica...
www.EngineeringMetallurgy.com
RE: Radio control racer needs an electrical mentor
I know Nic very well and admire his accomplishments but he SAYS he can't go much faster because he's burning up speed controls. His car weighs 11+ pounds (mine is 6.5), he has considerably more frontal area and down force and less rubber on the ground. On paper my car should be MUCH faster but the race isn't on the paper.
With lower amperage draw I should be able to run lower mAh packs thereby recouping some of the increased weight of 12s vs 8s batteries. Castle has a 12s speed control but I haven't been able to open the tech sheet on their site. I'm going to have to bite the bullet and spend some bucks because I seriously doubt that I can add 50 mph to my speed with only regearing!
RE: Radio control racer needs an electrical mentor
What the heck is that supposed to mean?
RE: Radio control racer needs an electrical mentor
I had a good laugh at that as well. At a guess, I'd say it means that whoever designed the body used a computational fluid dynamics (CFD) program to tweak & optimize the body design, in essence using a 'virtual wind tunnel' for testing. Either the article author, or the person (s)he interviewed was confused by the jargon.
RE: Radio control racer needs an electrical mentor
I'm glad you guys don't get it either.
RE: Radio control racer needs an electrical mentor
Up to a point, yes. However, the best performing bullets are boat-tailed, and the noses are not perfectly pointed, but instead, the meplat is small and flat. Of course, much of that may have to do with consistency, rather that outright speed. Competition is more about accuracy, although a faster round is less affected by wind. All designs are compromises, so certain features may be sacrificed to achieve some other result.
TTFN

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RE: Radio control racer needs an electrical mentor
RE: Radio control racer needs an electrical mentor
With the voltage and kv of the motor this thing should continue winding until 45-50k.
Any ideas?