Fisher Price Gearbox

My team is interested in using the Fisher Price Gearbox to raise our arm. The only problem is that we don’t know of any way to connect the gearbox to a sprocket that will run the chain to the gear on the pivot point of the arm. Are sprockets that would work with #35 chains sold? Or is there some kind of work-around?

For this plan, would I have to find a way to make them myself?

Get some octogon stock that will fit tightly into the white output part on the FP tranny. Put a hose clamp around the outside of the white part. You now have something you can bolt into or put a shaft with keyway into. Your location is Los Angeles but I don’t recognize the team number. If you can get to Hermosa Beach I can show you what we have done over the years.

BTW we stole the above idea from Kingman (team 60) years ago. The only time we had a problem was when a programmer (who shall remain nameless) left our arm against a hard stop when testing a new program version. Of course the motor went the “wrong” way and I wound up rebuilding an FP tranny. Fortunately we had several around.

I just did a casual search of McMaster-Carr for octagon stock, and I seem to be batting zero. Where does one go to get octagon stock?

I can vouch for this method as well. used in 04/05.

Also, cough * Joe Ross* cough

McMaster sells it up to 2" page 3510

Thanks. I understand what you’re saying about how to do this, I’m just wondering where I’ll be able to get the part (octagon stock, that is). I couldn’t find anything on google, and my team doesn’t really have the resources to manufacture something like this (no CNC machine or anything). Do you have the link to a place that sells/makes this type of piece?


I went to that site but I only see hexagonal bars. Could you be more specific? thanks.

I couldn’t find any either and I checked the usual suspects.

I guess we just made our octogon pieces. They are not high precision. The way we mount the FP gearboxes has lots of slop. The ones we made were 1" or 1 1/2" thick. You could machine them out of square stock if you have a mill.

If not you can use a band saw. Lay out an octogon of the proper size on the aluminum plate. Cut the shape out wit a band saw, taking care to make clean cuts. It is OK to be slightly oversize. Then file down to the layout marks. If you really have to, you could probably use a hacksaw, but it is hard to get a good cut that way.

I guess I don’t understand what you mean? They have hexagon bars in the correct size. What are you looking for?

Fisher Price sells a hub that fts over the white piece. It is flat on one side and with a spacer you can bolt a sprocket to it. We ran a 1/2" shaft through the middle and made the spacer fit to that. You’ll need to put a collar on the shaft to keep the hub from coming off the white piece.We did it on our 2005 robot. We used two FP transmission/motors facing each other with the sprocket between them. I couldn’ find a good picture of the assembly. If you need one PM me and I;ll see if I can get a picture in the next couple of days. (yes! we still have all of our previous years robots around!)

Good luck!

Here’s a pic showing both methods mentioned on this thread…

On the top FP Transmission we’re using an octogon adapter with a hose clamp that we made back in 2003.
On the bottom Transmisison we’ve used the plastic coupler that FP sells (used to come in the kit) and acually broached it and stuck a shaft through it. We have also bolted plate sprockets directly onto that plastic coupler.

BTW: That setup was all for prototyping purposes only.

Here is a link to a picture of the hub!
Check out part # 33 on this drawing.
This is a link to a place that sells the parts.

they want octagonal bars.


I found myself in a similar conundrum today. Thankfully I found this thread. I was able to rough-cut half inch nylon (or whatever the plastic is) and then using a belt sander and patience, get a rough octagon that fits snuggly in the FP gearbox.

Then there’s getting the hole in the middle. That’s the real pain, if you do it rough like I did. I tried using an old FP gearbox (we have a dozen, I think) as a guide for the hole. Didn’t work too well, wobbles a lot and I had an off center hole. I also had the entire gearbox swinging around when it got jammed on the 15/32" drill bit that was in the drill press. :ahh:

I’m glad that I, a mentor, didn’t delegate that task.

I’m going to redo both octagons it using a turntable that mounts on the mill’s table. (drilling the center hole first)

Good posts, thank you all for the ideas.

If you’re in the business of manually making an octagon without precision tools, here’s what I’d recommend: Draw it in CAD, mark the center in CAD, print it out 1:1, cut it out, use 3M spray adhesive on your material, stick your drawing to it, get a cuttin!

Quick question: I’ve found 2 sources of data for the gear ratio of this gearbox. One says it’s 124:1, the other says it’s 188:1.

Can anyone confirm?

For the teams that have driven arms with the FP through the gearbox, have you run into any issues with heat? Specifically when you are holding the arm at a set position (up in the air). I know the FPs are cooled by fan blades that spin when the motor spins, so it seems to me that heat may be a problem when the motor is exerting torque but not spinning.

I’m not totally sure that this is the exact coupler used by these motors, but my team ordered two of them (they’re only $4 a piece) to see if we can make the FP gearbox outputs a little more useful.