pic: Fisher Price gearbox

[nixiebunny]

Wood is good.
TheR/C car world has a lot of 32p and .8mod gears available too.

[MrForbes]

old white, new orange. Different tooth count, too

[Richard Wallace]

I count 72 teeth on the orange driven gear (and 25 on its inner driver). Can anyone confirm?

Looks like the octagon hole could be drilled out to 3/8" and then broached hex fairly easily. A three jaw should locate center well enough, if my 72 count is correct.

[MrForbes]

We have a several of the old white first stage gears, so we decided to make a new gearbox for the 2012 robot. It is integrated with the shooter, the lexan panel it is mounted to will be the side panel of the shooter. We do need to make a new shaft, since the one shown here was fabricated in a prior year. The lexan plate that holds the motor and the hidden bearing was made tonight by students, using a 7/8" Forstner drill bit, and a small drill press. We just measured the gear spacing using a vernier caliper, laid it out carefully and drilled it. The motor is not really at tight fit in the hole, but it's good enough. If you have a way to ream or bore the hole to the proper size, that would be better. Note that this is the 2011 motor with it's 19 tooth pinion gear, not the 2012 motor.

The shooter wheel will be mounted on AM hubs, keyed to a 1/2" shaft, which will be bored to fit over the new transmission output shaft. We will probably use a roll pin or two to hold the shafts together.

[Tom I]

Originally Posted by squirrel

We have a several of the old white first stage gears, so we decided to make a new gearbox for the 2012 robot. It is integrated with the shooter, the lexan panel it is mounted to will be the side panel of the shooter. We do need to make a new shaft, since the one shown here was fabricated in a prior year. The lexan plate that holds the motor and the hidden bearing was made tonight by students, using a 7/8" Forstner drill bit, and a small drill press. We just measured the gear spacing using a vernier caliper, laid it out carefully and drilled it. The motor is not really at tight fit in the hole, but it's good enough. If you have a way to ream or bore the hole to the proper size, that would be better. Note that this is the 2011 motor with it's 19 tooth pinion gear, not the 2012 motor.

The shooter wheel will be mounted on AM hubs, keyed to a 1/2" shaft, which will be bored to fit over the new transmission output shaft. We will probably use a roll pin or two to hold the shafts together.

Very nice design! I will say my design is kinda parallelling this, but with 2 FP's and it's build into a piece of 1.25" C-channel. How did you pin the gear to the axle? just a roll pin?

Also, we had a 3/8" axle but found that if we tried to bore out a 1/2" shaft to fit around it to direct-drive it, we'd have a 1/16" wall around the circumference, which is relatively weak. Instead we bored out a 5/8" shaft and drilled out the center of our AM hubs to attach it to the throwing wheel. If you're worried about the strength of the 1/2" shaft, try that.

[MrForbes]

The shaft is 3/8" hex, with the ends turned to fit into the 3/8" ID bearings. The older FP first stage gear happens to have a 3/8" hex hole in it.

I was thinking we might step it down to 5/16" where it enters the 1/2" shaft, or possibly make a larger diameter coupler to fit over both shafts (for example, by turning the end of the 1/2" shaft to 3/8", and using a short length of 1/2" od 3/8" id steel tube)

[Tom I]

Originally Posted by squirrel

The shaft is 3/8" hex, with the ends turned to fit into the 3/8" ID bearings. The older FP first stage gear happens to have a 3/8" hex hole in it.

I was thinking we might step it down to 5/16" where it enters the 1/2" shaft, or possibly make a larger diameter coupler to fit over both shafts (for example, by turning the end of the 1/2" shaft to 3/8", and using a short length of 1/2" od 3/8" id steel tube)

Yeah I was fearing that... We were trying to avoid getting the hex shaft. We have the capabilities to do so, we just didn't want to make that investment... I'm thinking we'll give pinning it a try, and if that fails we'll have a hex shaft ready to go.

Okay, glad to see you guys are thinking about connecting the two the right way. Let me know how it all comes together! (It's kinda scary how our two designs are similar... our turrets are basically the same as well)

[ToddF]

I suspect this is one of those cases of design convergence around a common goal. We are doing something similar, except using a steel center gear with a 3/8" bore keyed to a 3/8" dia wheel shaft. I don't trust that a plastic gear will hold up to the shock loading the gear mesh will see when the balls are fed into the shooter.

[Tom I]

Originally Posted by ToddF

I don't trust that a plastic gear will hold up to the shock loading the gear mesh will see when the balls are fed into the shooter.

We've done it before in Lunacy. The plastic gear seemed to do pretty well, and this was the year we named our robot the "Noisy Cricket" because the wheel was spinning so fast... yeah. But as long as the gears are mounted properly and the teeth mesh well, you shouldn't have a problem. Metal gears will also do you well but again be sure the gears mesh well.

[Matt C]

On the bright side, Andy Mark now makes the CIM-Sim. We've got one year and with two motors on it she screams like a banshee.

http://www.andymark.com/product-p/am-0932.htm

[ToddF]

If only you could actually buy one.

I've come to the conclusion that the only way to get a robot done ahead of time is to drop tons of cash on transmission components before the season starts, and hope they are legal.

[Matt C]

I guess we got lucky, we purchased ours last week.