Pressure angles for motor pinions

[Ian Mackenzie]

In all the data I've managed to find on the motors in the kit, the pressure angle of the gears often seems to be missing. I know that the Fisher-Price pinion and the smaller diameter part of the brass gear for the Chiaphua motor are both 32 diametral pitch, but what pressure angles are they (20 or 14 1/2 ?)

-Ian Mackenzie
Team 188

[Joe Johnson]

The Chiaphua gear is NOT 32 DP. It is a 36 DP gear. It is also not standard in that it uses a 25 degree pressure angle AND it is enlarged -- the gear data is on the print that I posted on this site and (less legibly) in Update #1 from FIRST.

The Fisher Price IS a 32 DP gear. It is a more or less garden variety 20 degree pressure angle, full depth gear (the profile is not quite the standard used for steel, but it is close enough for anything we at FIRST will ever care about).

Before you ask, the drill motor is a standard, 0.7 module, 20 degree pressure angle, full depth gear.

Joe J.

[Larry Barello]

How do you suggest we connect to the Chiaphua gear cluster? Are 36pd 25deg spur gears available off the shelf?

[Kit Gerhart]

Originally posted by Larry Barello
How do you suggest we connect to the Chiaphua gear cluster? Are 36pd 25deg spur gears available off the shelf?

The 36 PD, 25 deg gear is very non-standard, so your main choices are probably to use the gear cluster that came in the kit, or make your own wire EDM gears.

The small gear on the cluster is standard 32 pitch. Only the one mating with the motor shaft is weird.

[Larry Barello]

Great: the driving gear is standard. That is what I needed to know. I can gut the Fischer Price gearbox for further reduction of the Chiaphua.

[Joe Johnson]

Having a 5:1 reduction from the Chiaphua be the INPUT to a gearbox designed for the Mabuchi motor as input is likely to produce a lot of small plastic shards (wear your goggles please).

Seriously. At 5:1 the Chiaphuas have as much torque as the window motors but have the speed of the drills in high gear. Believe me this is not likely to be a good thing.

Joe J.