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Originally Posted by Squirrelrock
hopefully, one belt will be kept tensioned by the 2pulley assembly being pushed downwards far enough to keep friction between the 2 pulleys that the belt is running over, and the other belt (there are two, one for each gear reduction) is kept loose so that it is not affecting the driven speed.
thanks for your input!
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In order for any belt transmission to work, the entire belt must be in tension. Modern cars use a belt tensioner to compensate for stretch, think of a pulley on a spring arm. The idea from
M. Krass is one good way of doing it.
The tension needs to be so high that a 12" unsupported belt segment will deflect less than 1/2" with about 10 lbs pushing on it (assuming a 5/8" V-Belt or 19 mm Poly (flat) belt) to keep it taut. If the other belt is fairly loose, it will slip enough to be insignificant - BUT it will have a tendency to fall off the pulley.
Dayton or Grainger probably have belt transmission formulae on their web sites, how many HP a given belt can transmit. If one Horsepower is about 746 watts, and a CIM motor draws 20 Amps at 13 volts, you have about 1/3 HP, and most any belt will handle that happily.
There are different belts with different amounts of grip. My snowblower uses a belt to drive the auger, and it has a clutch. If I use too grippy of a belt, the clutch never releases. The 'wrong' belt has 'not for clutching applications' written right on the 'box'. I say this because the loose belt will still have some grip, and that can be a problem with the wrong belt.
What you propose will work, but I recommend building a prototype and a lot of testing, especially long-time testing to gauge durability. Hook up a motor and let a belt slip a bit (and the other grip a bit) for a week, see what happens.
Don