pic: Fisher Price gearbox

This is a first for team 1726; never before have we fabricated a custom gearbox. This one was made by several students today using some 1/8" aluminum (holes punched with a Rotex Punch) and 3/4" birch plywood as a standoff.

The FP motor has a stock pinion, and the other gear is the first stage reduction out of the plastic gearbox. Since this gear comes with a hex bore, we just had to turn down a hex shaft in the lathe to make it work. Total reduction is 4.5:1, so whatever it’s turning will be going pretty fast. :slight_smile:

(By the way, if Andy Baker is reading this… when are you going to come out with some sort of fisher price spur gear box? A kit that came with just the sideplates, standoffs, bearings, and output shaft would be incredibly useful! If made right, it could interface with a stackerbox, too… and it would save us all this pesky manual labor :stuck_out_tongue: )

But the manual labor is half the fun!

Looks good for the first time! Let us know how this works out for you.

The manual labor wasn’t so hard, it just took a while :stuck_out_tongue:

We got this bolted on and made the part it drives today (video coming soon, watch for a thread in Robot Showcase), and it seems to work great. The trickiest part about this was getting the spacing between the motor and bearing holes right, and armed with a trusty 64ths inch ruler, we got it close enough that the gears mesh fine. At full speed it didn’t seem to have any problems.

video of it in action, turning a roller, which does not do anything yet :slight_smile:

The 2012 FP gearbox is worse in terms of usability. I took one of ours apart, and it has orange gears with small octagonal holes instead of 3/8" hex holes.

I’m thinking about boring out the gear on the lathe to fit a 1/4" or 5/16" round shaft and using a metal hub to clamp the gear to the shaft. A bit of extra work, but life’s like that.

We need Kevin to weigh in, then we’ll have five Forbeses on one thread. A new record!

I heard that… and I was disappointed. Fortunately we have lots of old gearboxes stocked up from previous years, so we have lots of lightweight plastic hex bore 20dp gears laying around. R24 seems to grant us access to use them all that we want. I saw at least 10 gearboxes in the shop, you need any?

If you have access to a mill, you could probably machine an octagonal shaft if needed. It sure is easier to use off-the-shelf hex stock though.

There’s no way this is safe.


Anyways…interesting, we need to take apart the new FP transmission, and see what it’s like, and also see how many old ones we have. I know we have two of the old white first stage gears, but we may need one more if we do what we were discussing last night for transmission for this year’s robot.

We were planning on using a single stage FP motor/gear to drive the shooter, and a two stage to drive the collecting roller/conveyer.

Now why would I go and do a thing like that?

How many old FP gearboxes does 1726 have laying around? Perhaps we could borrow a gear…

I love the simplicity of this design, and may copy, er em… use this idea if we find a need for it. I love re-using the parts already supplied to us.

My only concern is that shock loads might cause a bit more damage to the plastic gear in this configuration. When the full gear set is used, there will be less impact on this pinion/gear interface caused by shock loads, like the ball going through the shooter.

I know it’s early, but have you seen any problems yet, or anticipate any?

In true 2791 fashion, we were considering copying the wisdom of the Forbes family. But we’ll probably stick to the aluminium gear we got off of SDP-SI instead of the plastic FP gears, because we don’t have any good FP transmissions lying around. Cons of being a younger team, oh well.

Our team did a similar design, taking a FP blue gear; then putting it in a toughbox chassis. We bolted two 9013 motors to it and attached it to our prototype shooter. It sounded like a bloody circular saw and ran nearly as fast as one, here’s the results:

As you can see, not quite the results of bolting a CIM to the shooter:

Oh well, time to make our own ratios/gearbox!

P.S one of the students destroyed it by running the motors reverse when it was at full speed! Snapped a 9013 shaft and ruined the plastic gear, oops!

You don’t need to use FP gearbox gears, apparently. I googled the fisher price pinion gear pitch and found a CD thread that says that the FP gear is 0.8mm module, which translates to 31.75 diametral pitch.

McMaster Carr sells 32 pitch nylon gears in useful sizes for cheap!

We’ll try this out.

neat! but they don’t have the magical hex bore in them…

btw I found the gearbox from the original picture, it’s in good shape still and we can swipe the gear and bearings and possibly the motor from it.

The wood spacer is really nifty…

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

old white, new orange. Different tooth count, too

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.

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.