pic: FP Gearbox (KOP Gears - 2)

Made from the CAD Model Posted Here:


This Gearbox used gears from the Black KOP Fisher-Price Gearbox.


This CAD is so good it looks real! :stuck_out_tongue:

It looks like the pinion on the motor could disengage the first stage reduction under load if the gearbox isn’t completely tightened together. Should be easy to fix though. It looks good!

Great work!

Next step… beat it up, test it, study it, take it apart & put it back together as fast as you can, break it then fix it, install it, run it for 40 hours… then make a list of your lessons learned and go back to the drawing board!

Design is an iterative process…


Nice! I’ve got one that looks almost exactly the same, no hex bore bearings on mine though. As you might have figured out from my response to you earlier post, I never measured anything. Mine was built like a wooden boat, build one part and fit the next one to it. Continue 'til done.

Now it’s got to go on a robot, and as John says, test, break, rework.

Good job,


neat! I’m curious why you used hex bore bearings, just turn the ends of the shafts round instead…that’s how we made our single stage FP gearbox and it worked fine. easy to make, we had the bearings laying around already

We eventually added a 2nd gear parallel to the gear the motor pinion is touching to keep the 2 FP motors from stripping gear teeth off of that gear. We turned the extra hub off of one to fit it in there, it ended up being the difference maker and kept the gearbox running all year w/o any problems.

I can’t tell from the photo, did you remember to make slots or holes for the air to circulate through the motor? I also can’t tell if the pinion is making full engagement with the gear. It looks like the engagement is at the very end of the pinion. A thinner side plate (or a recess in the current one) will move that closer to the motor’s bearing and make life easier on the motor shaft.

I’m guessing the use of the hex bearings eliminated the need for any lathe work. That’s a nice option for teams without access to a lathe.

How are you locating the hex shaft axially?

Brandon, That is a great idea. I think we will end up doing the same.

Funny thing, our whole bot used hex bearings and I think we had over 100 bearings laying around along with over a bajillion bushings. So we have the option of .5 bore, .375 bore, .375 hex bore. So I figured I could be lazy and just use .375 hex all the way.

This was before we added the holes for the air, I relized from another CAD drawing I had that I didn’t add the holes for circulation. The pinion fully engages when you tighten the gearbox.

Thanks for the help,


Thanks John,

I’m going to share this with the team, every team should do exactly what you described. Rookies and Veterans. I have a feeling that I’m going to make a sign with this your quote on there.


Where did you purchase the .375 hex bearings?

We didn’t exactly “purchase them” they are kinda homemade but it doesn’t take any efforts at all to pop out 50+ in about a few hours.

For the 3/8ths bearings, we bought these supplies from mcmaster carr:

-1/2 bore bearings (6383K234)
-1/2 OD - 3/8 ID Bushing (6338K414)
-One 3/8th Hex broach (2875A19)

All we did is place the bushing over the bearing. Then we broached and pressed the bushing in at the same time. They all worked great, We made about 100+ bearings this season. It makes life 10x easier not to have to lathe down the ends, we do have access to one, but we found it easier to interface everything with hex.


I’ll also vouch for this technique. However we never really needed to “press” the bushings into the bearings, they should kind of slide in snugly.