Mechanical Engineer needs a Small Motor
Mechanical Engineer needs a Small Motor
(OP)
Built a John Fitch steamboat model for the museum, and need to get a proper drive motor. The boat is 7 feet long, a replica of the first commercial steamer in the world, 1790 vintage. The model is powered by live steam or electric power, with radio control. The boat can be seen at: http://www.youtube.com/watch?v=u_G5U7wcWQo
A slow speed steam engine drives the rear paddle mechanism, and a small 8VDC 5A, 2000 RPM motor below deck (about 2 in dia x 4 in long, 1/4 in dia shaft) is connected to the engine crankshaft via a small (1/4 inch wide) timing belt at 10:1 ratio. The timing belt drive has very little friction.
The PM DC motor has ordinary DC switching, proportional forward and reverse, and when running in electric mode the motor drives the paddle mechanism and continuously cranks the steam engine. This all works very well.
When running on steam power, the concept is to use the de-energized motor only as a flywheel, remaining connected to the steam engine, through the timing belt, and turning ten times as fast as the steam engine. The problem is the “notchy” nature of the de-energized motor, and it takes considerable torque to turn over the de-energized motor. I would like to find a similar motor that would spin freely when de-energized, but have no idea if this type of motor exists, and if indeed these physical characteristics are even within the realm of being obtained.
I want to avoid installing a clutch between the engine and motor if possible. Any suggestions from the EE community?
Thanks in advance for any help.
A slow speed steam engine drives the rear paddle mechanism, and a small 8VDC 5A, 2000 RPM motor below deck (about 2 in dia x 4 in long, 1/4 in dia shaft) is connected to the engine crankshaft via a small (1/4 inch wide) timing belt at 10:1 ratio. The timing belt drive has very little friction.
The PM DC motor has ordinary DC switching, proportional forward and reverse, and when running in electric mode the motor drives the paddle mechanism and continuously cranks the steam engine. This all works very well.
When running on steam power, the concept is to use the de-energized motor only as a flywheel, remaining connected to the steam engine, through the timing belt, and turning ten times as fast as the steam engine. The problem is the “notchy” nature of the de-energized motor, and it takes considerable torque to turn over the de-energized motor. I would like to find a similar motor that would spin freely when de-energized, but have no idea if this type of motor exists, and if indeed these physical characteristics are even within the realm of being obtained.
I want to avoid installing a clutch between the engine and motor if possible. Any suggestions from the EE community?
Thanks in advance for any help.





RE: Mechanical Engineer needs a Small Motor
Benta.
RE: Mechanical Engineer needs a Small Motor
Some motors sacrifice a little power output to get smoother operation by skewing the slots of the rotor or stator. This means that there is no 'perfect' position where the magnetic poles of rotor and stator align along their full length, so the cogging is less pronounced.
Specialised motors from the likes of Portescap have no iron in the stator which means that they do not suffer from the problem at all. They are expensive and typically reserved for servo applications. Wound field machines typically have little to no cogging, although finding one small enough for your application might be a little harder these days.
RE: Mechanical Engineer needs a Small Motor
The motor may be oversized for your application. Measure the current draw when the motor is working normally. For example; if the current is only 1/4 of rated current the motor may be oversized by a factor of 4. If you can use a smaller motor the "cogging" may be reduced to something that you can live with.
You may check Benta's suggestion by disconnecting the motor from the controller to see if it makes a difference.
Bill
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"Why not the best?"
Jimmy Carter
RE: Mechanical Engineer needs a Small Motor
You need a motor called "ironless rotor" design: they can be designed to have absolutely 0 cogging torque so would solve your problem. since it is for a museum I would be happy to offer one to you from my old stock if it would fit. Kollmorgen PMI pancake motor, see typical specs here:
http://www.kollmorgen.com/en-us/products/motors/br...
they typically are similar 2-3000rpm with 8-12v at 4-8amps input. but they are larger diam and very short. I assume also you do not need a tach on it?
Let me know if one will fit.
RE: Mechanical Engineer needs a Small Motor
http://www.ebay.co.uk/itm/PORTESCAP-Motor-with-gea...
RE: Mechanical Engineer needs a Small Motor
RE: Mechanical Engineer needs a Small Motor
Yours
Bill
p.s. lps
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Mechanical Engineer needs a Small Motor
RE: Mechanical Engineer needs a Small Motor
Nice offer too Mike.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Mechanical Engineer needs a Small Motor
Beams are cheaper than wheels. Like it.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Mechanical Engineer needs a Small Motor
We UPSed you the U9 motor early last week. In the meantime one of my contacts came thru with a smaller version - about 2.5" dia (I emailed you specs and drwing) as you wanted for this boat. It should be here this week. I sent you a couple emails but maybe your or my spam filter ate them? Let me know if you want the smaller motor also.