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Need to increase efficiency during flywheel ramp-up

Need to increase efficiency during flywheel ramp-up

Need to increase efficiency during flywheel ramp-up

(OP)
  I'm currently using a small (35mm can) motor to ramp a 2" dia x .5" wide flywheel from 0 to 15K RPM in ~ .5s.  Because of the inefficiency of the motor at the low-end range, I am exploring both mechanical and electrical improvements to the current design.  I belive that you can link to the motor discussion here:
  http://www.eng-tips.com/gviewthread.cfm/lev2/11/lev3/47/pid/237/qid/35300

   I'm making this thread to see if anyone out there has a mechanical solution to the problem.  What I'd like is a compact continuously varibale transmission design or a auto-shifting gear set-up.  The main point is to increase efficiency in the low-end range of the ramp-up.  I'm open to anything.
   Any ideas?
   

RE: Need to increase efficiency during flywheel ramp-up

Glad to see you got here Rich.  I'll try to define the constant mesh transmission better and how it would work in a four or six speed implementation.

Talk at you later,

Bruce

RE: Need to increase efficiency during flywheel ramp-up

Do you mean efficiency? If so then this is way out of my league.

However, if you just want a faster ramp-up for a given motor power could you use a stored air supply blowing on the rotor to get it going?

Cheers

Greg Locock

RE: Need to increase efficiency during flywheel ramp-up

(OP)
Greg,
  No dice.  I am looking for efficiency. Also, packaging concerns keep me from being able to have ompressed air storage handy.  Thanks for the suggestion.

RE: Need to increase efficiency during flywheel ramp-up

What about a centrifugal variable pulley? I believe I saw one advertised, we considered one on a design.

That way the motor starts out with high torque, the pulley changes diameter with speed, and transfers from high torque to high speed.

RE: Need to increase efficiency during flywheel ramp-up

(OP)
stressriser ...   Thought about this, but never got it down to a reliable method in my head.  Can you give me any info on the part you looked at (manufacturer, etc.).  Any help is greatly appreciated.

RE: Need to increase efficiency during flywheel ramp-up

Rich, streesrisers has a good idea.  Take a look at the transmissions used in snowmobiles and auto-trans ATVs.  If you could minaturize one of those you'd be a big step forward.

Bruce

RE: Need to increase efficiency during flywheel ramp-up

Me again,

  I decided I may as well describe the transmission to you if you're not familiar with them.  Stressriser might be interested as well.

  These tramsmissions are, by necessity, belt driven.  Both driving and driven sheaves are split types.  The driving sheave is held open by a spring and the driven is held closed by a spring.  The driven pulley also acts as a clutch, being forced open wider than the belt.

  Weights incorporated into the pulley force the sheave halves together at a given motor RPM.  As the motor speed increases, the sheave continues to close further, walking the belt out toward the rim.

  The driven pulley responds to the increasing tension on the belt by opening against the pressure of the integral spring.  Thus a very wide range of ratios is provided over a comparatively small range of engine RPM.

  A later development of these transmissions was load-sensing capability.  In this development only one half of the driven sheave is connected to the output shaft.  The other half of the sheave is free to rotate (to a limited extent) about the shaft.  The two halves interact through a ramp and follower arrangement.

  As tension on the drive belt increases there is a small amount of belt slippage on the 'fixed' half of the sheave, but since the 'free' half is not under similar tension it does not slip to the same degree, but instead rotates slightly relative to the 'fixed' half such that the two halves are forced closer together by the ramp and follower system.  This forces the belt further out in the sheave which in turn forces the sheave of the driven pulley to open wider, and an increase in the (reduction) ratio results.

  Hope that explains how they work.  Where to find a miniature version is beyond me.

Bruce

RE: Need to increase efficiency during flywheel ramp-up

(OP)
Bruce,
   The idea I was working on previously was close to the tension style you have suggested, but I couldn't figure out a way to get this to work correctly without a tensioner. I'll think a little more about the ramp and follower idea.  maybe I could get this to fit cleanly inside the design.  
   I'd prefer to stay away from the swinging weights, as I think it could cause balance issues if placed on the motor and not dynamically balanced and I am concerned about bushing and brush wear if this happens.
   Anyhow, thanks for the knowledge.  Keep it coming.  We'll get this thing solved before too long.

RE: Need to increase efficiency during flywheel ramp-up

What would a variable frequency drive get you?
Does this compromise low end torque?


RE: Need to increase efficiency during flywheel ramp-up

Hi Rich,

  It seems as soon as I leave the computer another idea pops into my head.  If you can measure the RPM of the motor (which is incredibly simple with a 3-phase motor), you can use a servo (as in model aircraft) to force the driving sheave halves to any position you desire.

  This adds electronics (trivial) and the servo, while eliminating the swinging weights.

Bruce

RE: Need to increase efficiency during flywheel ramp-up

  I got so exited about the variable speed transmission I forgot what I came here for.  Spiral spring.  One revolution, controlled by escapement.  Motor winds through gearbox between cycles.

Bruce

RE: Need to increase efficiency during flywheel ramp-up

(OP)
Bruce,
  You and I think a lot alike.  I checked into the spiral spring idea a couple of weeks ago.  I need about 6 turns to get a good benefit in the system (from the spreadsheet), but with the torque that it would need to take up (~ 4 in-lb max), the spring ended up to be too wide to fit into my pinion (about .75").  
   We already have electronics caplable of this in the system.  I'll check into the servo idea.  Think I could make it work.

stressriser (I like that name by the way),
   Thanks for the info on the torque converters.  I'll probably pick one of these up and see if I could shrink it into my system.  It would be exactly what I'm looking for if I could get it to fit.
   

RE: Need to increase efficiency during flywheel ramp-up

(OP)
Roach,
  By variable frequency drive, do you mean an AC motor with a special controller?  Not sure exactly what you are referring to here.

RE: Need to increase efficiency during flywheel ramp-up

I mean an AC inverter that converts an AC power feed to DC, and rectifies it back to a different frequency to decrease RPM of the motor.  We use them all over our facility.  We use them to ramp up ( control acceleration) of our motors.
They have all kinds of inputs that allow for different configurations.
Problem:

In doing this, the motor maintains a constant torque rating from 60hz (standard freq.) down (approx.),and loses torque above 60Hz.  This may not be what you want considering you would have to size the motor large enough to supply a start-up torque for the flywheel, when you are really looking to size the motor for the torque required to maintain rotation of the flywheel at 15K RPM.

Just a thought.
Not the answer for efficiency I don't think, but I learned something in the process.



RE: Need to increase efficiency during flywheel ramp-up

I recently saw a magnetic "shear pin" coupling from Rexnord. The principle this works under would allow you to get your motor rpm up quickly while transmitting a lower torque to your flywheel, which would allow it to catch up to the motor speed. The Rexnord website describes their product as follows:

"The Rex MagneLink coupling works on a
                                       fundamental principle of nature involving
                                       permanent magnets. The magnetic
                                       coupling consists of two separate
                                       components that have no physical
                                       contact. Precision-machined, aluminum
                                       rotors containing high-energy, permanent
                                       magnets are mounted on one shaft, and a
                                       hub conductor consisting of a steel
                                       housing with copper ring mounts on the
                                       other shaft. The coupling's ability to
                                       transmit torque is created by the relative
                                       motion between the copper conductor and
                                       the magnets. This motion creates a
                                       magnetic field in the copper that interacts
                                       with the magnets, thus transmitting the
                                       torque through the air."

They don't make a coupling as small as you need but you could possibly apply the same principles to a smaller coupling. You may end up with more inertia for the coupling than the flywheel, however. But that can be said about a number of the mechanical solutions.

RE: Need to increase efficiency during flywheel ramp-up

A couple of suggestions that may help reduce current draw of your motor during startup:

I used to race model cars in my younger days (now race real ones!). My experience was with electric motor cars which used small DC motors ('05' size) running on DC (7.2 V) batteries and controlled with a MOSFET electronic speed controller. Anyway, to reduce the wasted battery energy lost to heat the options were:
1) Electronically limit the current to the motor through the speed controller
2) 2 or even 3 speed automatically shifting geared transmissions (check model racing car suppliers - you may be able to adapt an existing suitably sized unit from a 1/8 th scale IC racing car)
3) Slipper clutch type arrangements - friction and/or fluid types were/are used on 1/10 electric racing cars.

With luck you may be able to find something off the shelf that will do the job, or at least can be further modified.

RE: Need to increase efficiency during flywheel ramp-up

(OP)
DVD  ... Interesting idea.  It would get rid of the heat losses that I would get with a slip clutch, but would have the same positive effect.  I'll check into it.  Thanks for the suggestion.

RX ... Current limiting doesn't help us in this instance because we are using an all inertial load (current limiting just increases the time in the low-RPM range.  It does help our batteries however, so we may do a little of it in the end.

   I'm already fitting a 2 speed RC car tranny to our system.  My simulations show it should get me about a 30% performance increase.  I'll post my results when I get the test run (today or tomorrow I think).

RE: Need to increase efficiency during flywheel ramp-up

Epilogics has a very ingenious (and somewhat complex) design for an infinitely variable transmission.  Unlike most other designs, theirs is NOT friction-based.  Here's a link to a very brief description of the device:

http://www.epilogics.com/corp/index.html

There isn't much info on the web site - you'll have to call them to get more.

pdr@baymachinedesign.com

RE: Need to increase efficiency during flywheel ramp-up

Before you try to increase the efficiency perhaps it is
worth to check, why you are worried about it ? Energy
cost, overheating ( and MTBF ), etc.? Perhaps there is an
easier or cheaper solution !

<nbucska@pcperipherals.com>

RE: Need to increase efficiency during flywheel ramp-up

The magnetic coupling will also generate heat when there is a relative slip between the coupling halves. Think about induction heating.

RE: Need to increase efficiency during flywheel ramp-up

(OP)
dvd ... good point, I didn't think it all the way through.  forgot about the induced current and the resistance heating.  Thanks for the reminder.

nbucska ... I need efficiency for 2 reasons.  One is heat related (durability, cooling, etc.), but the other is cycles per charge.  I can add cooling fans, fins, etc. to get the some of the heating down (although battery heating would be extremely difficult to dissipate effectively), but the cycles per charge cannot be impacted positively by anything other than an efficiency improvement.

RE: Need to increase efficiency during flywheel ramp-up

  Rich, a comment on this one.  Although energy loss due to heating was the first thing that crossed my mind, if this coupling allows the motor to operate at a more optimal current flow then you'll still have a net gain in efficiency.

  If we go back to basics, for maximum efficiency we need the motor to operate under (variable) load conditions which will keep the motor within its optimum current range.

RE: Need to increase efficiency during flywheel ramp-up

Hi Rich,

I do not know how important is your search for efficiency in the cost-result curve involved, but here are my two cents
Why not turn the flywheel into a motor itself?
You can build a synchronous type motor; by drilling your flywheel six holes 60 degrees apart, ¾ inch diameter each (and if you need to avoid air friction, you can fill them with nylon plugs or polyurethane). You should place 2 U shaped coils, whose magnetic circuit are 30 degrees phased of each other, then, you can close alternatively each coil’s circuit, at an increased frequency, making your motor gain speed very fast, and not loosing power. This should be the most efficient way to do it, since mathematically you could know how fast it will accelerate, and therefore increase the frequency as needed
Sancat

RE: Need to increase efficiency during flywheel ramp-up

(OP)
sancat... Wouldn't this design require the use of electrical energy to generate both the rotor and stator fields?  Then wouldn't it be difficult to get to the higher efficiency ranges seen with PMDC motors running at high speeds?  I understand how I could get more low-end efficiency, but I do not yet see how I could increase total efficiency with this type of system.  Do you have any links to synchronus motor curves that are close to what you are suggesting or any idea on the highest efficiency I could see with this type of motor?  Thanks for the post.

RE: Need to increase efficiency during flywheel ramp-up

Rich,
Well, I do not have curves at all for this <<device>>, but you could be right that a Perm magnet motor could do better. I thought you just wanted to accelerate the thing and not have it running steady.
So why dont combine both ideas; you could use a magnet and some carbon steel to build a magnetized flywheel with the desired dimension, and provide a rotating magnetic field that increases its frequency, perhaps using a variable frequency drive. Some can provide frequencies as high as a 1000 hz, and they are off the shelf. With 500 hz, and a 4 pole configuration, you could achieve 15000 rpm
sancat

RE: Need to increase efficiency during flywheel ramp-up

The best way to gain your effiency is to keep the motor running at rated speed. The rotating mass of the flywheel offers energy to the task being performed. If the task robs all of the flywheel energy, your starting from zero on each cycle. Very inefficient by design. Retain energy in your flywheel after each cycle to keep your motor speed within an acceptable range. This of course can be achieved by reducing the task load, or increasing the flywheel energy. Adding gadgets inbetween  will increase your inefficiencies.

RE: Need to increase efficiency during flywheel ramp-up

(OP)
automatic2...
  Unfortunately, I can't do that, for 2 reasons:  The first is this is in an application where the mechanism will be moved between cycles and the gyroscopic effect of moving a flywheel of 3x the necessary inertia will definitely be unacceptable.  Also, since the cycles are very sporadically placed, the energy necessary to maintain the flywheel at the high speed becomes a big source of loss (it is a battery operated mechanism).

  The short answer is...  If I could I would, but I can't, so I need to add gadgets in between to make the efficiency the best I can get it under the circumstances.

RE: Need to increase efficiency during flywheel ramp-up

Sounds then that the flywheel does not serve your purpose. You may well need a wind up, release style device where the motor builds tension between sporadic cycles. Regardless, similar to the flywheel concept, you'll need to provide enough energy storage to maintain anticipated duty cycles. One would need to know the power required per cycle and the consumption rates to make usefull suggestions. Maybe you could list your criterim.

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