Timing Belt Style (Gear) Reducers Experience

[richards]

Building a belt-drive transmission is not difficult. I've built several different models out of Polycarbonate, aluminum and Delrin. All worked equally well.

I'm attaching a simple drawing that shows the three main pieces:

- Motor mounting plate

- Base plate

- Spacer

In the jpg file, the Blue parts are 3/4" round spacers, the Red parts are the timing pulleys (20 tooth and 60 tooth), the Green parts are the shaft collars.

You could make the motor mounting plate and the base plate out of 1/4" plywood or 1/2" MDF to test the design and then make the final parts out of Delrin or aluminum. The large holes near the center/bottom are for bearings. I used 1.25" outside diameter bearings that fit a 1/2" shaft. Both the flanged bearings and non-flanged bearings work. I used the flanged bearings when I made the plates out of 1/4" material.

The spacer plate was cut from 0.08" thick aluminum. The hole in the middle is sized to fit the protruding 'ring' on the motor. It is simply a 'filler' plate so that the front of the motor sits fully against the motor plate.

The distance between the motor's shaft and the axle is 3.25", which allows the use of a 150 tooth XL belt (assuming that you use a 20-tooth pulley on the motor and a 60-tooth pulley on the axle.

I used some rubber O-rings between the shaft collars and the bearings to allow the bearings to turn freely.

Be sure to have a machine shop bore the pulleys for you. Trying to drill the holes with a drill press will probably leave you with parts that are off-center. A machinist can use his lathe to accurately and quickly bore the holes.

With the standard Alpha motors, a 3:1 belt drive driven through a 25-tooth spur gear (1.25" pitch diameter), will give you 0.001309" per step (assuming that you use the standard 1,000 steps per revolution on your Alpha stepper drivers).

With Oriental Motor PK299-F4.5 or PK296-F4.5 motors and Geckodrive G203v or G201x stepper drivers, you will have 2X better resolution because the Geckodrives use 2,000 steps per revolution.

With a 3:1 reduction, torque will multiply by 3X.

[Gary Campbell]

Mike....
When you say "standard alpha motors" can I assume that you are NOT referring to the 7.2 TH motors that are standard on the current PRSalpha? Note: this is clarification for users of PRS machines, as the current alpha does not suffer from a lack of resolution with the 7.2 motors. Backlash, IMHO, and holding power may be another story for those that use them hard.

My prototype solution above requires replacement of the existing 7.2 motors and integral gearbox with different model Oriental motor and belt reduction box. Also requires reprogramming of the driver along with another set of unit values.

[gc3]

http://www.mechmate.com/forums/showthread.php?t=3138

There are also several other threads about this on this site.