pic: Flat 4x 775pro Gearbox

I was tinkering around in Solidworks, and this is what I came up with. It’s a 4x 775pro (or Redline!) gearbox that’s geared 17.65ft/s (adjusted). It’s completely flat, which saves a lot of space – most of the assembly fits within the 2" of a WCD.

Why are you cantelievering the small cluster gears instead of putting the second bearing in the front plate and having the clusters shafts pass straight through the middle plate?

Also, how would the weight change if you pass the output shaft all the way through, pocketed the back plate so the bearing flange sits flush with the outside of the plate (to not interfere with the motors), then got rid of the middle plate? I feel like that would make it even lighter with minimal performance impact if it works geometrically.

Agreed on both - and if you ditched the middle plate and keyed/hexed the output shaft the whole length between the bearings, you could reverse the shaft to a flipped configuration with the same pieces.

The render doesn’t show, so let me ask - did you cut some vents in the motor plate to vent the motors?

What’s keeping the cluster and output shafts from sliding out?

I’m guessing the weird output and middle plate are a consequence of trying to keep all 4 775Pros in a horizonal line with each other, which also necessitates two cluster gears.

I don’t think that tradeoff is worth it - you could get a bigger 32DP center gear to use all 4 motors around a single cluster gear, and then run the output shaft either forwards or backwards at your convenience, with just two plates.

On top of both of these things, is there any reason you didn’t put all 4 motors on one driven pinion? There should be plenty of room to cluster the 775s in a square pattern to all drive one pinion on one side rather than one on each. This should save weight and space, but it would also not have a linear layout like you have, so if the thin/wide form factor is what you were going for then just ignore the question.


Running all 4 motors on one cluster gear will result in that cluster gear seeing more wear. This is something we noticed last year on 2451 with a 4x 775pro gearbox. With the correct material used for the cluster, it will be fine but splitting it to two cluster gears is not the worst idea, and to get the height profile the OP was looking for it makes perfect sense.

But I mean it doesn’t matter because all 775pro DTs are crap and anyone who does one is/should feel bad.

Hey Aaron, this looks good.

I definitely agree with the comments about removing the middle plate. I think you could get rid of that without too much finagling. You could also probably make it a flipped motor gearbox, but I’m not sure it’d really benefit you. The speed is a little zippy for my tastes, but it’s not a huge deal and speeds are game dependent anyway, so who knows. I do think you need to put a little more thought into how you’ll mount this to the tube. I love using hex head bolts, but I doubt you’ll want to cut clearance holes for them in your tube. Also, might wanna add in however you’re venting the motors now to sort out any problems early.

How did you calculate the adjusted speed? I’ve assumed 70% voltage when calculating adjusted speeds for 775 gearboxes. 70% is a conservative limit based on testing by my teams and others.

TLDR; using the standard 81% efficiency number isn’t very useful if you won’t be running the motors at full power

Yeah, so in general I just wanted to make a flat 775pro gearbox that could serve as a drivetrain gearbox. With regards to the middle plate, when I look at it now I can see that it would be pretty easy to take it out. That’s what you get for CADing at night I guess.

In any case, thanks for all the feedback! Some thing I just forgot to add, like the 775 vent holes, but I’ll need to rethink some other things.

It’s also worth noting that the 2451 cluster gear had a very small face width. The COTS 32DP gears available from WCP and AM have much wider teeth, reducing stress on each tooth.

70% power != 70% voltage.

70% voltage = 49% power.

70% power = 83.7% voltage.

But I mean it doesn’t matter because all 775pro DTs are crap and anyone who does one is/should feel bad.

Literally no one credible has made this point.