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        Help! DC motor transmission puzzler

#1 gavib Feb 04, 2013 03:12 PM

DC motor transmission puzzler
 
Hi all,

I have a small model design problem which I 'm hoping you may be able to assist with resolving.
I 'm a software developer by trade and so am quite inexperienced in the engineering/build area of a project, though pretty good at complex Arduino coding!:D

In its simplest form, my issue is this;
I have a fairly high-torque 12v DC motor driving a basic pulley and belt transmission in both clockwise and counter-clockwise directions.
What the design requires is that the motor shaft be automatically disconnected from rest of the system when there is no current being supplied to the motor, in order that the pulley may be freely rotated by hand.

Some kind of clutch would seem to be the answer but I am unaware of any which would suit this purpose. Most are built for large industrial purposes and are far too large for hobby modelling designs.
I have investigated spring, electo-magnetic and centrifugal types on the internet but am no closer to a solution... so I thought I 'd ask some experts!

Any help or advice you could give would be VERY much appreciated. :)
TIA
Gav

#2 Dcope17 Feb 07, 2013 01:27 AM

RC heli centrifugal clutch possibly...
Weed eater clutch or if needed a scooter or motorcycle centrifugal clutch.

All depending on RPMs and torque.

#3 gavib Feb 07, 2013 03:14 AM

Thanks for your reply - much appreciated!

Torque is 0.14 Nm (1482 g.cm)
RPM is around 200-250 rpm

As you can see, these figures are quite typical of a 12v DC motor, but not in the same ball-park as that required by scooter/motorcycle clutches.

Never heard of a 'weed eater clutch'! Will investigate :)
Gav

#4 Roto Rob Feb 11, 2013 07:20 PM

I low cogging (detent) motor might be an alternative.

#5 Dcope17 Feb 18, 2013 12:29 AM

The clutch on my weed eater works on a 1.1HP engine. It has a spring that holds the friction things in and when the RPMs are high enough, the friction parts start touching the bell and gets everything spinning. The advantage to this is you can test different springs to get it to act how you want it to...

#6 Roto Rob Feb 22, 2013 04:06 PM

He wanted to drive the motor in both directions. Most clutches don't work well in reverse. So if going that route would probably need two clutches.


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