pic: 571's new gearz loose weight

[JessR]

Originally Posted by sanddrag

Well, I knew the gear comes from sdp-si already but I find the other information extremely useful. Thanks so much. Do you think something like a 8mm bore with 2mm keyway and .24 length through bore would hold out? The actual keyway (length and width) would only be slightly smaller than what you are using. I would be gearing the Drill down to match the Chia. ...

Sandrag -
1. Regarding key size - Yeah, as you know 8mm & 2mm is essentially the same size as the 5/16 & 3/32. (7.9mm & 2.38mm or so) Our designer chose that shaft size somewhat arbitrarily - 1/4 diameter would probably also work.
The limiting factor here strengthwise is the yield strength of the keyway in the plastic gear - (weakest component in the plastic gear- steel key- steel shaft load path)
You need to find average pressure on the plastic keyway surface at max motor torque = stall torque. It needs to be below the yield strength of the plastic. And - We usually use a safety factor of 3 or 4 to account for impact loads etc.
You can analyze this pretty easily -
I would get the motor stall torque & gear reduction - find stall torque on the shaft (it's going to be 3-4 x motor torque)- and then divide by shaft radius to the midpoint of the keyway to get force acting there.
Divide by keyway area, and see if it's above the yield strength of the plastic.
[If you don't have a strength, many engineering plastics are around 3000 psi yield.] You may have been here already.

2. Re: synchronizing/reducing drill & fp motor speeds to a common shaft - see my lengthy description in last post, it should be clear. I can always email you some more photos of tranny from different angles. We have them around there in some directory.

3. I think one key in an efficient design at this first step of reduction is to keep your bearing friction down, (ie use ball bearings & smallest possible dia.) these first shafts off the motors are spinning 1000-3000 rpm, and thats a lot of rubbing goin on if you use large diameters or bushings. Still, bushings are cheap and that's worth a lot.

Jesse.