pic: 4x flipped 775pro gearbox

Hopping onto the bandwagon and trusting that it works.

Geared for 8/18 ft/s adjusted with a 3" wheel, which is the size of wheel that doesn’t cover up the back of the 775pros.

Now that I have this, I think the packaging would work out much better if I abandon 2 speeds. I’ll post that one later.

This. I like this. Compact? Check. High power? Check.

Can you provide us with the gears you chose so I can do some thermal modeling on it, and make a few educated models on how it would perform under “real” performance?


Few questions:

  1. How much does it weigh?
  2. What’s keeping the first cluster stage aligned? (It looks like it’s only supported by one bearing)
  3. All of the yellow gears I’m assuming are VexPro gears, and the first stage are WCP gears, but what is the black dog gear?
  4. Any plans on releasing the CAD?

I don’t know 1) and 4), but for 2) it looks like a 3/8" hex shaft is just barely visible behind the standoff. For 3) WCP recently released a 30t dog gear this year.
Really great work Chak! I think you could use a larger wheel given that there is a 2x1 behind the 775s anyway. A 3.25" would raise your top speed to ~20fps which might be better for a gearbox like this.
EDIT: Holy cow I didn’t realize that was adjusted speed. The screenshot you posted puts the free speed at 23fps, which is perfect.

It’s hard for me to tell, but it seems to me that you could get the motors above the wheels if you wanted

What’s the black sprocket for?

I would assume for WCD

Ahhhh okay. I wasn’t visualizing it right :yikes:

Looks great! One question, does this design include holes for air intake on the mounting face of the motor?

Just wondering, is that something that is needed for all 775pro gearboxes to work, or are just leaving the vents for the fan open okay?

Those front holes are for the fan, See examples here.

The fan at the back draws air into the motor through the front vents, and also some from the holes on the back face, and expels that air out of the slots on the diameter. Blocking the front holes removes the critical air flow path across the armature of the motor where a significant portion of the heat is generated. Putting these slots in the gearbox plates isn’t difficult.

(Also this is a really clean setup, I quite like it)


Gonna start off by saying that this thing is fricken sick! It’s beautiful. My concern with it would be with the tabs of the motors facing outward what the likely hood of clipping something and tearing a wire and a tab right off of one of the motors?

The likelihood of something like that happening is very low, there is an additional 2x1 and then probably 1.25-1.5" of Colson then a 3.25" wide bumper which means that the motor tabs are at least 5-6" away from other robots.

Thanks everyone! Here’s the link to the updated version of the model, now with encoder mounts, air vents (thanks pmangels17), and minor fixes for interference. In the same folder, you can find the single-speed version of this gearbox. It’s much thinner without that pesky shifting piston or the dog gears.

Sure. Here’s a screenshot of the JVN calculator configured to this gearbox.

  1. about 7lbs without bolts, but with the 2 sprockets and everything else.
  2. and 3. were correctly answered by Anand
  3. Sure.

But yeah that’s an option, with the 2 speed and chain outside tube. With one-speed and chain-in-tube, I can bring the motor 2" closer, right up to frame perimeter. :cool:

Yep, by either using chain-in-tube, abandoning 2 speeds, or both.

Alastair is correct. But yeah, of course it’s still more risky than facing the motors inwards. However, I think the risk is low enough to take, especially in a game like this year where extensions beyond bumpers are rare. Besides, even if a single motor gets ripped out, the drivetrain can still run the rest of the match at a slower pace and later get the motor replaced in the pits relatively quickly.

It looks nice! I especially like how thin the single speed is (even though there’s something nice about a shifting gearbox). I also like the 1/2" OD bearings to turn a live axle gear into an idler. I’m definitely going to be stealing that for future designs. It looks like on the single speed your mounting pattern is covered in the middle by the output stage gear so you can’t bolt all the way through (which is what I’m assuming your plan was). Should be an easy fix. The other things is that idler gear is small, taking the load of the entire gearbox, and buried in the middle of everything with no access point. If that thing shears, you’re not going to have a fun time replacing it. I would say definitely use a steel gear, and maybe think if you can add a way to access it without taking apart the whole gearbox. Other than those small points, looks great!

This is really slick. I was playing around with an idea like this yesterday in Solidworks and then saw you posted this. Will definitely check out the CAD models, thanks for sharing.

Thanks for sharing this! It seems like an awesome design.

I have been looking at making something similar, but I’m having a hard time finding a cluster gear that is the right size for the initial stage. Would you mind sharing where you would source the 85t 32dp gear in your model?

I believe AndyMark carries one: http://www.andymark.com/product-p/am-3533.htm

Thanks! I don’t know how I missed it!