Help: Motor and Worm Gearbox Torque
Help: Motor and Worm Gearbox Torque
(OP)
Hello. I hope somebody will be able to help.
I have designed some equipment to assemble some large parts. It involves a stand and a fixture attached to it via a worm gear box.
The fixture and part needs to tip over at 90 degrees, from vertical to horizontal, and back.
After design and build, the specification has changed. I am not sure if the motor is going to be strong enough.
The total weight being lifted is 120kg.
The distance of mass from the pivot point is 280mm.
The current geared motor is 0.127 Nm. It is planetary geared to 100:1. Roughly I think this gives 12 Newton Meters.
The motor output Rpm is 60.
I have hooked this motor up to a 30:1 NMRV worm gear box, because 60rpm is too fast. I ideally wanted to rotate the fixture 90 degrees in less than 10 seconds, but no more than 20.
I have read that the calc for Final Torque is: Initial Motor Torque x Gear Ratio.
I have therefore taken the original motor torque and multiplied it by 130:1 total gearing. 0.127 x 130 = 16.5 Nm.
So far so good?.....
My weight is 120kg at 280mm from pivot. To get this back into meters, I have divided One Meter by 280mm, which gives 3.55. (Ie, 280mm fits 3.55 times into a meter).
120kg divided by 3.55 = approx 34kg at 1 meter. For certainty I am calling it 35kg.
So I have a mass of 35Kg at 1 meter from the pivot, which is then being worked back through a 30:1 worm gear box, then back to the 100:1 motor gearbox.
Is any of this right?
Can anybody help me understand what I now need to do with this 35kg, to know what the output torque of the motor needs to be, prior to the 30:1 gearbox?
Ie, taking the motor as it is now, at 12 Nm, or 16Nm through the second gearing, would this be enough to lift the weight?
Sorry if this is hard to understand, or something that is normally very simple for you guys. (Automation and motors etc are not usually my kind of work).
Many thanks
Sirius.

I have designed some equipment to assemble some large parts. It involves a stand and a fixture attached to it via a worm gear box.
The fixture and part needs to tip over at 90 degrees, from vertical to horizontal, and back.
After design and build, the specification has changed. I am not sure if the motor is going to be strong enough.
The total weight being lifted is 120kg.
The distance of mass from the pivot point is 280mm.
The current geared motor is 0.127 Nm. It is planetary geared to 100:1. Roughly I think this gives 12 Newton Meters.
The motor output Rpm is 60.
I have hooked this motor up to a 30:1 NMRV worm gear box, because 60rpm is too fast. I ideally wanted to rotate the fixture 90 degrees in less than 10 seconds, but no more than 20.
I have read that the calc for Final Torque is: Initial Motor Torque x Gear Ratio.
I have therefore taken the original motor torque and multiplied it by 130:1 total gearing. 0.127 x 130 = 16.5 Nm.
So far so good?.....
My weight is 120kg at 280mm from pivot. To get this back into meters, I have divided One Meter by 280mm, which gives 3.55. (Ie, 280mm fits 3.55 times into a meter).
120kg divided by 3.55 = approx 34kg at 1 meter. For certainty I am calling it 35kg.
So I have a mass of 35Kg at 1 meter from the pivot, which is then being worked back through a 30:1 worm gear box, then back to the 100:1 motor gearbox.
Is any of this right?
Can anybody help me understand what I now need to do with this 35kg, to know what the output torque of the motor needs to be, prior to the 30:1 gearbox?
Ie, taking the motor as it is now, at 12 Nm, or 16Nm through the second gearing, would this be enough to lift the weight?
Sorry if this is hard to understand, or something that is normally very simple for you guys. (Automation and motors etc are not usually my kind of work).
Many thanks
Sirius.






RE: Help: Motor and Worm Gearbox Torque
I have used an online convertor to convert 35kg force per meter into Newton Meters.
35kg is allegedly 343 Newton Meters. To get the motor torque, would I then divide this by the 30:1 gearing on the worm box?
343 Newtons per meter divided by 30:1 gearbox - 343/30 = 11.43 Nm.
My original Motor is capable of 12 Nm.....
Am I doing this right?
Many thanks.
RE: Help: Motor and Worm Gearbox Torque
This is the output torque of the 30:1 gearbox. Without consideration of the frictional losses (which will be significant, in a worm-drive gearbox) this will require 330 / 30 = 11 N.m input torque.
That is also the required output torque of the first gearbox (without considering friction). Since this one is simply 100:1, the required input torque of that gearbox, which is the output torque of the motor (not the gear-motor ... the MOTOR), is 0.11 N.m. If you bought an integral gear-motor (motor + gearbox combined) and you have the output torque and RPM of that gear-motor then the internal contents of that gear-motor are irrelevant to you. The gear-motor has to output 11 N.m (plus something for frictional losses in the subsequent mechanism).
Frictional losses in that worm-drive gearbox are gonna getcha, though. The efficiency of a worm-gear reducer varies depending on the design of the internal gears ... but it's never very good.
RE: Help: Motor and Worm Gearbox Torque
Sticktion may be more important than friction.
"Anecdote on"
Many years ago a particle accelerator called Triumf was constructed. (Tri Universities, Meson Facility)
Part of this was a large chamber operating under a vacuum.
A number of motor driven screw jacks were used to lift the top of the chamber when access was required to the inner part of the vacuum chamber.
Everything was calculated based on the friction of the gear reducers and the screw jacks.
The top of the chamber was lifted as expected.
Then there was an occasion to stop the lift partway and then continue.
Sticktion.
The motors did not have enough torque to overcome the sticktion and start the screw jacks when they were loaded.
After you have determined the friction that you must overcome, (The gearbox maker may list the losses of the gearbox) you may want to consider sticktion also.
Most motors will develop greater than nominal torque for a short period but we need some motor specs to advise you on the probable available torque.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Help: Motor and Worm Gearbox Torque
Brian, you make it sound so easy!
It looks like I have wandered around the houses to work things out backwards, but I had somehow come up with approximately the right answer.
Just out of curiosity, would you agree that the methodology I used is (kind of) right, even though this is not the proper way to do it?
Of course, yours is much more straight forward, thank you very much!
Waross, I have never even heard of sticktion before. I will have a look into that. I need to try and find some kind of figure to take into account the loss of efficiency for a 30:1 reducer too.....as things seem to be getting quite to the limit of the existing motor.
The motor is an integrated gear-motor. A "99.5:1 planetary/epicyclic, three stage reduction, all-steel gears with large-size carrier pins for high torque handling"....
Nominal voltage: 12V DC
Operating voltage: 3-18V
No-load Motor Speed (minimum.): 6000rpm
No-load Current (w/gearbox): 0.6A
No-load Speed after gearbox: 58rpm
Max. Efficiency Speed after gearbox: 48rpm
Max. Efficiency Current: 2.3A
Max. Efficiency Torque: 2.1Nm (21.4kg-cm)
Stall Current: 11.4A
Stall Torque, motor only: 1300g-cm
Stall Torque after gearbox: 11.9Nm (121.3kg-cm)
The worm box is something a bit like this, but without the motor mounting casting: http://www.power-reaction.co.uk/Catalogue/Gear-Spe...
Changing the voltage will cause issues with the control box.
To try and salvage this job, if the motor is a bit too weak after the efficiency loss, I have searched for a 12v motor with a higher torque and found this http://uk.rs-online.com/web/p/dc-geared-motors/773...
Output Speed 70 rpm
Supply Voltage 12 V dc
Maximum Output Torque 3 Nm, 25 Nm
DC Motor Type Brushed
Shaft Diameter 9mm
Gearhead Type Worm
Length 178mm
Width 60mm
Depth 100.6mm
Dimensions 178 x 60 x 100.6 mm
Current Rating 6 A, 34 A
Core Construction Iron Core
If this gives me 25Nm, and the other was 12Nm, I gather that this would more than cover for the efficiency loss.... so I suspect it is worth spending the money to make sure it works.
There is another motor for half the price which has an output torque of 14.7 Nm. This would be easier to fit because it is the same shape and diameter as the existing motor. However, is the extra 2 or 3 Nm enough for the efficiency loss?
Thanks again.
RE: Help: Motor and Worm Gearbox Torque
You should be using the maximum efficiency torque.
Stall torque is the maximum momentary torque.
Designing for continuous running at stall torque may result in early motor failure.
Friction is usually sliding friction.
Sticktion is static friction. The force required to start an object sliding.
From the specs of the second motor:
Continuous current = 6 amps.
Stall current = 34 Amps
I2R losses at stall current = (34/6)2 = 32 or 3200%
The good news is that with a ratio of stall torque to rated torque of over 5:1 you probably don't need to worry about sticktion.
But friction is not my field. Hopefully a mechanical expert will post a typical ratio of friction to static friction for a worm drive.
Running some gearboxes at maximum torque may result in overheating and/or early failure.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Help: Motor and Worm Gearbox Torque
I was thinking of ordering the second motor, from R.S. Components, but now, I don't know any more.
The calculation for the needed torque is now established to be about 11 Nm. The motor allegedly outputs 25 Nm, more than double.
I do not know whether this is the "stall torque" though. If it was, could it potentially handle around 20Nm without grumbling too much?
(I had hoped this 'doubling up' would be enough, including any loss in the worm gear reducer). The maximum strain would be the initial movement and upwards to -45 degrees or so, - then the weight of the fixture and the part would help do the work as it tips over the pivot point. Likewise for the return journey.
The fixture is not being constantly motored to 90 degrees and back. It will be loaded with a part, powered backwards 90 degrees, some work will be carried out, then it will be lowered. Then another part will be loaded, that part will be worked upon, then it will be tilted back, then worked upon again, then lowered again for unloading and then loading a new part.
The fixture caters for several similar parts, not all of them are needing to be tilted back, so at worst case scenario it will be a "day shift" of usage on that particular part number, with the operator doing maybe 4 or 5 parts per hour, if that helps. I am hoping, therefore, that it is less intense than a normal motor that would be whizzing around all day long...
I am struggling to find a 12 volt motor with a higher torque, particularly one which is easily available and not many £ hundreds. I might have to investigate adding some counterbalance weights to lighten the strain, but it is not ideal and won't look too professional.
Are you thinking that the DOGA brand motor (rated at 25Nm) will be too weak, or do you think it would be able to cope okay?
I may be able to get a different worm gear box, the same sort, but a ratio of 40:1 or maybe 50:1, depending on the extra time it would take to rotate it 90 degrees.....but I am not sure if any extra torque gained this way would make that much difference.
RE: Help: Motor and Worm Gearbox Torque
STALL TORQUE ON TAT MOTOR IS 25 Nm
Yes the motor will develop peak torque of 25 Nm.
However the motor will be overloaded at anything past 3 Nm.
Motor heating will be roughly (Actual torque / Rated torque)2
(11 Nm / 3 Nm) 13.4 or 1344% Even for a short period the motor may run a little warm at over 1300% of rated losses.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Help: Motor and Worm Gearbox Torque
As you may have guessed, I know next to nothing about motors, or torques, or amps and volts. My usual work is press tooling, jigs and fixtures to inspect components. It has been 20 years since I did any serious maths or science at college, because I have never needed to use it in all these years.
I am having to try and pick it up as I go along, flying by the seat of my pants (as usual).
I read the other week, when looking around for info on how to work out torques and gears (which may not have been the right thing) that the "Final torque" is the initial motor torque prior to gearing, times by gear ratio.
On this basis, I have been looking a the 3 Nm torque and assuming this was the motor torque before it went through the gears on the motor. After the gears, I have been assuming the motor outputs at 25 Nm. Maybe I am going completely wrong here. I hope it is not the case that the geared motor runs "normally" at just 3 Nm, but grinds to a halt and burns out at 25Nm. I would therefore be running it somewhere around half the burnout rate.
When I tap the search results into the RS catalogue selection, it states the motor has an output torque of 25Nm. The stall torque of the DOGA motor could perhaps be that, or maybe more, I am not sure. I am not sure what I am missing here. I had hoped this was the torque it could normally handle okay.
When you say that the motor will be overloaded at 3 Nm, this sounds disastrous....... 3Nm, and I need at least 11. Or are you saying it would lift it, but it would be getting red hot very quickly and would soon burn out?
Furthermore, I am also reading the specification as though the final output of the gear motor is 70 RPM. Looking at the catalogue PDF, now I am not even sure of that! It says on the RS configurator that the output speed is 70 RPM, so I am taking their word for that too, like the output torque.
I think I need the motor to give me somewhere between 58 and 70 RPM when working the fixture. (I need roughly 2 RPM by the time it is reduced 30:1 via the secondary worm gearbox it plugs into)
If the initial motor speed is 70 RPM, but this thing actually crawls around at say 10 RPM when loaded, by the time it passes through the 30:1 reduction, it would take an eternity to rotate the fixture 90 degrees.
https://www.rapidonline.com/pdf/560993T_v1.pdf
RE: Help: Motor and Worm Gearbox Torque
http://uk.rs-online.com/web/p/dc-geared-motors/773...
Output Speed 100 rpm
Supply Voltage 12 V dc
Maximum Output Torque 4 Nm, 40 Nm
DC Motor Type Brushed
Shaft Diameter 12mm
Gearhead Type Worm
Length 206.5mm
Width 60mm
Depth 122.7mm
Dimensions 206.5 x 60 x 122.7 mm
Current Rating 6 A, 60 A
Core Construction Iron Core
I could probably live with 100 RPM. It is a bit brisk, but it is better that than too slow.
Is this any better?
RE: Help: Motor and Worm Gearbox Torque
40 is stall torque.
4 is rated torque.
(11/4)2 = 7.56 only overloaded by a factor of 756%.
Getting closer.
Maximum Output Torque 4 Nm, 40 Nm
Rated torque is 4 Nm
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Help: Motor and Worm Gearbox Torque
If I needed 10Nm to lift 120kg - and it can handle 40Nm without grinding to a halt, would I not just be running it at 25% more strain than it ought to run? Would this be a problem?
I am sorry, I am not quite understanding whether I am miles out.
Being overloaded by 756% sounds like this motor I am aiming for is like me putting a Lego motor into a real world motorbike, and is thus a joke.
I really have no idea what I am doing with this any more.
I thought I was along the right tracks, but I may be about to spend a lot of money and make things worse.
I have been told that I cannot use a motor and gearbox combination (such as Bonfiglioni or Motovario) because the voltage is 230, and that we would not be able to reverse the motor back and forth at 90 degrees. Also, there is a 12volt linear actuator that lifts the fixture stand to different working heights. I was told this was also a problem if adding such a gear motor at that voltage, and that it was a lot more unsafe compared to the low voltage motors (in terms of operator electrocution).
RE: Help: Motor and Worm Gearbox Torque
Motors develop stall torque when starting. As the speed increases, the torque drops.
At stall the motor is badly overloaded.
Your current rating is 6 A, 60 Amp.
6 Amps is the rated maximum safe continuous Amps.
60 Amps is the momentary starting current.
Motor heating is mostly I2R
If you double the torque demand, you double the current. That means 4 time the heating.
When you see 4 Nm: 40 Nm, use the 4 Nm for design, not the 40 Nm
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Help: Motor and Worm Gearbox Torque
I can appreciate it must be frustrating for you when I don't know anything about amps, or I2R, or how this has been effecting the torque issue.
Well, it looks like I am up the creek without a paddle on this one. I really don't know what to do next.
All the controls and electrical equipment has been made to suit and power actuators and motors at 12 Volts (for the original requirement of 40kg, not 120kg). This was approx £1000, including safety stops, foot pedal controls, limit switches, relays, cables, electrical diagram supplied and so on. A linear actuator is yet to be bought.
When we did an initial test of this, clamping some 50kg (approx) steel bars on to simulate the original 40kg fixture, the existing motor seemed to lift it. It wasn't exactly eating it for breakfast, nor was the centre of gravity quite correct, but it did lift.
This gave me some hope that by doubling or tripling the torque of the motor, it would solve the problem. But maybe lifting it once or twice is different to a full shifts worth of usage, and I had no idea about the amp issues.
So....
12 Volts does not seem able to give us more than 40 Nm Stall Torque, or 4 Nm real torque, when we need at least 12 Nm.
24 Volts does not seem to give us much better, looking around, and would require a whole new electrical control box anyway.
230 Volts is too high, apparently, because the base of the fixture rotates 180 degrees and the wire to the motor comes up the middle of the stand.
I think they are (rightly) worried that eventually the cable could break and be a hazard, even though it is rarely turned and the cable is quite slack. Then there is the issue of the different voltage for the actuator, which seems to come in either 12 or 24 volts only, not 230, which maybe equally dangerous even if there were any available anyway.
I had hoped that the much higher torque motor, either ""25Nm"" or ""40 Nm"", would salvage all of the work done so far and allow us to use the 12 volt actuator too.
It could have been worse, we could have ordered the ""25Nm"" motor and the 12 Volt actuator and wasted another £300 or so.
Well, I guess it is time to go cap in hand to the bosses tomorrow, to tell them the news.
Maybe the only way out is to attach some great big counter weights on it, but I don't think the customer will be happy with that, they are expecting it to be sufficiently powered on its own - and with there being different product weights, this may get tricky to find a good balance.
Thanks again for your advice, it is sad to know things are so wrong with everything, but at least I have not thrown more good money after bad. Best cutting our losses now rather than make it worse. This job is just snowballing.
Cheers.
RE: Help: Motor and Worm Gearbox Torque
7 Nm or 8 Nm would be better.
BUT, make sure you are looking at the rated torque, not the stall torque.
If you can double the gear ratio that will be the equivalent of boosting the 4 Nm to 8 Nm.
If you can live with the reduced speed.
Here is a possible candidate:
Mode #319.4862.20.00, 12 Volts, 8 Nm, 45 RPM, 6 Amps.
http://docs-europe.electrocomponents.com/webdocs/1...
I hope I get this right:
30:1 and 45 RPM = 1.5 RPM
1.5 RPM = 40 seconds per revolution.
40 seconds per revolution = 10seconds per 90 degrees.
The implications on the motor:
(11/8)2 = about 190% loading.
Well, for 10 seconds you can probably get by with that short term overload.
Fell free to point out if I have missed something.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Help: Motor and Worm Gearbox Torque
I have tried to explain the situation to those involved in this job here, and the consensus (at the moment) seems to be that we'd better not risk buying another motor that may not be up to scratch for production use.
There are apparently another two of these to make in the future, so it may be best to just swallow the losses on this one and get it right, then balance the cost over the next two.
We have just done a test lift on the original motor.
The "maximum efficiency torque" for that motor is 2.1 Nm. It has lifted the 42 Kg fixture weight no trouble, and quite speedily. However, we added a weight of 20kg to the fixture and it would not even entertain moving. It overloaded the control box and we had to use the reset button. My guess is that the original motor would lift 50 kilograms.
However, I think you're trying to tell me that even though it can lift this 50kg, it would not be suitable for 8 hours of use in a production environment.
The 8Nm motor may therefore do it after all......but I am still a bit uncertain about it.
My simple brain is a bit too fried to check the rotation time, but it sounds about right to me. Anywhere between 6 and 20 seconds is feasible.
I have found a motor spec on the DOGA website, which is much better and runs at 12 volts.
It is the 258.3712.20.00 model. http://www.oem.co.uk/products/Motors/Motors_Geared...
The spec looks interesting, and I think it gives us 12 NM "normal" running.
It is 40 rpm, which is a bit slow, but as long as it is under 20 seconds or so, it may be okay.
I don't know how much they are yet. I am guessing at around £420.
I will need to discuss this further, to see whether it is worth the extra money, or to try the 8 Nm one for about £220.
What are your thoughts on the 258.3172.20.00 version?
Regards,
RE: Help: Motor and Worm Gearbox Torque
Be aware that your control device must be capable of handling the 55 Amp starting surge.
As a final check, check the current that the motor draws during operation.
The running current should be equal to or less than the rated 12 Amps.
Here are some comments on motor overloading and motor burn-out.
I hope that this is helpful to you when the question is asked:
"Well if the smaller motor worked once, why do we have to spend more money for a larger motor?"
Heat is the enemy of motors.
If the motor gets too hot, the insulation fails and the windings short out.
The motor has resistance. The heat developed in a motor may be expressed by the current in Amps squared times the resistance in Ohms.
The motor will radiate heat and lose heat by conduction and convection.
A balance is reached at a temperature where the heat lost equals the heat developed.
If this temperature is too high, the insulation fails and the windings short out.
A cold motor may be safely overloaded for a short time. But the time that the motor is overloaded must be shorter than the time it takes for the motor to reach a dangerous temperature. This must be followed by sufficient time at reduced load for the motor too cool down.
While it is possible to intentionally overload a motor for short periods of time, factors may change:
A motor may work well being overloaded for part of the operating cycle during the autumn, winter and spring but fail on a hot summers day.
The operating cycle may be changed by the operator to an operating cycle that no longer allows sufficient time for the motor to cool down between overloads.
You are considering a cycle of 10 to 20 seconds every 10 minutes. This is a good candidate for an intentional short term overload, or is it. An undersized motor may work well for years until the day that the operator, for whatever reason, runs 5 consecutive cycles with no cool down time and the motor fails.
Will that ever happen? Let's ask Mr. Murphy what he thinks.
I just got the memo back from Mr. Murphy.
He refers me to "Murphy's law" which states that this will happen and the motor will fail.
By the way, there are calculations for safe cyclic loading of a motor. In the Cowern Papers this is called "RMS Loading". These calculations may be applied to a machine where a motor is momentarily overloaded during part of a cycle. Some applications are punch presses and metal shears. These machines experience a very short momentary overload during the actual cutting or punching of the metal.
The cycle is known and is not subject to operator changes.
RMS loading will not be safe to use in your application. The operator may easily shorten the 10 minute cool down time to an unsafe interval.
Disclaimer: I am a Ft. Lb. type of guy. I don't generally work in Nm. I have accepted your Nm values without verifying them.
However, I accept BrianPetersen's values and your experience with the 2.1 Nm rated motor is further confirmation that we are in the correct ball park.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Help: Motor and Worm Gearbox Torque
The factory it is being installed in is very spacious and well ventilated. The English town it is in hardly ever sees any warmth or sunshine....(sigh!)...so environment shouldn't be a major problem. However, if they are exporting the two others to a foreign factory, it could be.
I am hoping that the intermittent use will be our saviour on this. From our rather selfish perspective, if it burns out in 4 or 5 years time, then the motor will have more than paid for itself and a new one could be installed. It is not a great attitude to take, I know, but we are up against it at the minute.
The operation is it doing could not be done any faster - it is somebody manually bolting steel brackets and things to an object. So it kind of takes 'as long as it takes', if you know what I mean. They would not be able to rive the hell out of it without being deliberately destructive.
We have contacted the motor suppliers for the 12Nm motor I listed last, and they are approximately £330, which is not so bad if it got us out of the fix......but the problem is, they are a whopping 10 weeks delivery. This has in effect ruled them out of the equation. The first fixture is due for delivery in about two to three weeks!
I have just been asking about the amps and the present control box. I am told that the present equipment cannot cope with the 55amps to run that motor anyway - and would apparently need significant re-working to make it do so. So again, that kind of goes against it, in sheer practicality terms.
In light of this, I have been told to order the 8 Nm version we discussed earlier. The thinking is that the 2.1 Nm worked fine on 50Kg. If we are at 8Nm, that is four times the torque that lifts 42kg (say 160kg). It may not work out that way, but we'd be much closer to the 120kg maximum they'd ever put on it. I may be able to figure out some neater looking counterbalances that look like they are part of the stand, if needed, to help too.
I would have preferred to change the capacity for the amps and wait for the higher spec motor....but the decision has been out of my hands now.
regards,
RE: Help: Motor and Worm Gearbox Torque
That would be when the operator for some reason lowers and raises the load several times without actually doing any work on the workpiece.
It happens. Just ask Mr. Murphy. grin.
In your position I would go with the 8 Nm motor. It sounds as if your supervisor understands and is willing to take the risk.
You may consider the following, if time permits;
We know the net torque required but we don't know the torque required including friction.
Consider ordering one motor and measuring the current under actual operating conditions. The current profile during a complete raise-lower cycle may be important.
I expect that the current will start low and increase as the fixture rotates towards the horizontal position.
Once we see the actual current profile required, we may be confident with the 8 Nm motor, or it may become apparent that a larger motor should be used.
The current as a percentage of rated current should be a good indication of the torque as a percentage of the rated torque.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Help: Motor and Worm Gearbox Torque
RE: Help: Motor and Worm Gearbox Torque
I am in the process of re-designing the stand (to fit the new style of motor and to make the pillar rise and fall with the actuator), and I am going to make sure that the other motor could also be fitted into the space, to make sure it could be easily swapped later, if the need arose.
It seems the equipment ''is what it is'' now, and whatever we do to it in the future is going to cost....either rewiring to a new amp rate, or rewiring for a higher voltage altogether.
So, if all hell does break loose later down the line, at least we have a chance at obtaining a motor that can lift it, which fits into the design. We can test this one out, then, if it is no good, we can at least get the order started ready for the next two builds.
The shape and proportion of this fixture is such that most of the work is done vertically, then the dead-weight is moved from vertical, backwards, over the worm reducer box, until it becomes horizontal.
I think the initial lift will be the struggle, because all the weight is at one side of the pivot point. Seeing as the fixture (and part) is very tall, when the fixture gets to about 45 degrees, the weight of the fixture will start help lift it the rest of the way, as the weight starts to move over centre.
Moving it back down to vertical again is not so bad, because approx 40% of the fixture is still going to be hanging at the correct side of the pivot point to help it back down. Hopefully this will also help reduce the strain on the motor and the amps etc.
Cheers.
RE: Help: Motor and Worm Gearbox Torque
I would prefer to wait for the right motor and make sure the cabling can handle the amps, but my hands are a bit tied on this now. The pressure is on to get it all finished and delivered. We couldn't wait up to 10 weeks for the other motor delivery. We will have to manage somehow, even if we have to resort to counterbalance weights.
There will be an operating manual supplied, in which we could highlight the limitations and issue some warnings. I know nobody tends to read them, but from my employers perspective (I suppose) they would kind of be 'covered' in an instance where it is clear the equipment has been abused.
The work cannot really be carried out on the job any quicker than the expected cycle time. If it was filling yoghurt pots, or powering a production line, I think there could be a risk of somebody new coming along and "cranking it up"..... but in our case, I don't tend to see it as being applicable. Sure, somebody may end up pushing for 6 parts an hour instead of 4, but it may not cause that much trouble to do so.
We could attach a badge saying no part over a certain weight is to be used on the equipment, etc, too, for what it would be worth.
RE: Help: Motor and Worm Gearbox Torque
"Look at how this works, Charlie."
"Hey that's neat. Show me again."
"OK"
"Wow. Nice, do it again."
"Hey Sam. Come and look at this go up and down."
Or something similar. Actions leading to failure may not always be reasonable, or logical.
Bill
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"Why not the best?"
Jimmy Carter
RE: Help: Motor and Worm Gearbox Torque
If this is for an industrial environment or anything of the sort, why are you using 12 volts? Automotive motors for power windows and seats and windscreen wipers and the like are obviously 12 volts DC. But in my part of the world, anything industrial is either going to be 24 volts DC for low-powered equipment, or 120VAC single phase or 600VAC three phase.
There's no way I'd size something for an industrial environment close to "the edge". A motor that is perhaps a little bigger or stronger than it actually needs to be, you pay for once, and you never hear of it again. If it's only operating intermittently, make sure it can handle being operated continuously, but just beware that frequent starts and stops can be worse for a motor than just sitting there running steadily. If you slice the design and the motor sizing right down to the edge ... and you make a mistake ... and things don't quite work out as planned ... now you'll be doing it again, and this time it'll cost more.
The torque on your mechanism is pretty significant. It means your final stage reduction gearbox is going to have to be a decent sized unit to have the proper torque rating. Why try to operate this with a little microscopic motor that's just barely up to the task?
The power output that you are talking about for this application is somewhere near 70 watts. You need more because of friction, stiction, starting inertia, and the like, which everyone else has mentioned. That's into the region where AC motors start making sense. If you put a proper industrial (say) 1/2 horsepower AC motor on there with a proper gearbox from SEW Eurodrive or the like and which has the proper torque and speed ratings (and don't forget to pay attention to the overhung-load ratings on the shaft!!), it's gonna work, it's not gonna break, it's not gonna burn up, it doesn't matter how many times the operator hits the "start" button, and you'll never hear of it again. If you need variable speed then put a small VFD on the motor. Done. And if the end user somehow does manage to break it, they can get another one from the local Eurodrive distributor.
Yes, the initial price tag might be a bit more. Do it right ... or do it again.
RE: Help: Motor and Worm Gearbox Torque
RE: Help: Motor and Worm Gearbox Torque
In answer to your question about the 12volts.....it was just the way the job evolved. It started off being a very simple stand, with a tipping device (worm reducer)on the top to rotate an aluminium fixture plate at 90 degrees. The whole stand also had to rotate 180 degrees too, on a rotary base. The initial spec we were given was a maximum weight of 40 kilograms.
The idea behind the cheap worm box was that we'd just stick a crank handle on there and they'd tip it over by hand - with the option of adding some kind of motor (or air driven device, or even some kind of power-drill attachment) later. It was low volume work, so we did not see there being a problem with just winding it over with a handle. The motor was just a "what if" thing, which also sold the idea of using the reducer as a mechanism instead of gas struts, springs, counterweights, and so on (which would have been a nightmare, considering all the different weight parts being put on it).
This is how we set off. We designed and fabricated the stand first. It was all done, finished and powder coated. In the meantime, the customer had more meetings and decided they couldn't live with a handle on it, as the workers may complain due to the frequency of use they now had planned. It had to be driven. Oh, and the stand now had to be able to rise and fall too....!
So, not knowing anything about motors, or AC or DC or amps, I was tasked with finding something cheap-ish to remove the handle, and something to power the stand up and down. (Bear in mind that the original max weight was going to be 40kg).
Mistakenly, as I now know, I made a rough calculation at what I thought would handle 40kg and a factor of safety....so I was looking at the the stated "Torque Output" on the motor as being 11.9 Nm, and thought this would do it. I now know this is the "stall torque" and not the actual "output torque" for normal working of the motor. The linear actuator, from the same supplier, was 12 volts and could handle 400kg.
The customer then said they hadn't the budget for that yet - and could we send them the 'fixed height' tower, with the motorised tilting top on. It needed foot pedal controls, relays, limit switches - and they decided they only wanted the top to tilt when the stand was turned away from the operator. So, we bought the motor, got somebody to get the electrics for the control box, added microswitches, safety stop button, and so on.
So there it was, a tower that went 180 degrees and back on the base, with a motorised tilting top, and we attached some 50kg weights to the top and powered it back and forward quite easily. Great, we thought. All that would be needed next, when the next quarters budget clears, is the 12v actuator and a modification to the stand to make it go up and down.
In the meantime......we start investigating the fixture requirements. It developed from what we were initially shown, into something that, itself, weighed over 50kg without even a part being in it! No longer was it a simple plate, but a much more complicated and larger thing. I whittled the weight down as much as possible to around 40kg. But we knew the stand would only lift this, not much else.
So here we are, £1000 or so for the control box, then a motor, worm drive reducer, all at 12 volts. Let alone all the design hours and manufacture based on those things. The customer offers to pay for something to beef up the motor.....but we are told our whole electric control box would be scrapped if we change the voltage. We say we may have to factor in that loss and g to 24 volts.
In the meantime, I try and learn how to properly work out the torque for the new maximum weight - which is now 120kg and not 40kg. I was not too sure I had it right, but I was coming out with about 12Nm. Looking at 24volt gearmotors, the torque was only ever a fraction more than the 12 volt ones. It was overall so slight that it hardly made sense scrapping off the £1000 control box and equipment.
I thought we may have to go to industrial motors, three phase or single phase, 230 volts. However, we were told from the electrician we hire that 230 volts on this equipment would be dangerous, we were better at 12 or 24, preferably 24, and that it would cost a lot of money, the motor may be hard to reverse, and the because the power cables go up through the middle of the stand, twisting 180 degrees and back, it would be a hazard if that cable eventually broke inside the stand. We asked about some kind of rotary connector to power that kind of voltage, and he said they'd be far too expensive. Also, that splitting the cabling off to run a 24v actuator at the same time as a 230v motor would add extra issues.
So, I started searching again for 12 volt motors. Bigger ones. Putting in the specification values of "speed" "voltage" "output torque".....
I found some that had an output of 25Nm! Wahey!! I only needed about 12! So I thought we were going to cream it, save the equipment, save the design, and continue with the 12 volt actuator too - which we could have added to the existing control box with little work.
I wanted to make sure I was not working things out wrong though, so I thought I'd ask online about the torque. Again, it was found to be 11Nm or so......and you know the rest.
So, that's the tale.....and indeed, it is a lesson learnt in more than one ways. 1) Ensure we nail down all the specifications first! 2) Go for a more than adequate motor based on those specs! or may be 3) Steer well clear of anything that adds motors and electrics to our normal work!
Cheers.
RE: Help: Motor and Worm Gearbox Torque
Yeah, I can relate to that. Been there ... ! ! !
RE: Help: Motor and Worm Gearbox Torque
One can drop a lot of torque that way.
RE: Help: Motor and Worm Gearbox Torque
Keith Cress
kcress - http://www.flaminsystems.com
RE: Help: Motor and Worm Gearbox Torque
Fortunately for me, every step in the escalation was priced and approved.
In the end we spent $20,000 on parts and were congratulated on a job well done.
That has happened once in my lifetime and I don't expect it will ever happen again.
Bill
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"Why not the best?"
Jimmy Carter
RE: Help: Motor and Worm Gearbox Torque