pic: 2 speed flipped 4 775 pro gearbox

designed for 4" wheels
2.2 lbs without motors (with motors 5.3lbs)
18/1 high gear giving it a speed of 16.19 ft/s adjusted
46/1 low gear giving it a speed of 6.28 ft/s adjusted
designed for chain in tube WCD
I would love some feedback!

I like the design, but I would personally choose not to use it on a west coast drive train. I prefer to use CIM motors for drive trains, and 775 motors for object handling and linear motion (elevators, etc.). Another thing that concerns me with this design is that you would probably not be in a good position if you got in a pushing match with a west coast drive using a 3 CIM shifter. I could see those motors getting smoked if you pushed them too far.

Nevertheless, your design looks like it would be good for a game where robot size is extremely limited, because it allows for extra space between gearboxes (assuming you are using them on a west coast drive train) to fit components.

That’s all I the advice I can give without looking at the CAD. if you could post it, I would be able to get a closer look at it and maybe give some more advice.

Not sure if you’ve been around CD recently, but there have been several discussions on the merits of 775s in many applications in the past few months. A search for “775pro drive site:chiefdelphi.com” on Google will bring up many relevant results to peruse.
The TL;DR is that 775pro drive gearboxes are ok with caution. A 8-775 drivetrain will very easily live the season with current limiting or 30A breakers on the motors.

Love the design. Very compact, and I love the offset gear to save space. One thing I have to mention is that the motor mounting plate looks pretty heavily pocketed and thin; changing to 1/4" material there might be prudent, and making the webbing thicker.
For free speed I’m getting about 18.5fps with a 4" wheel. That’s not a bad free speed, but may be a little fast even with 4 775s. It really comes down to how your driver is handling it, so if you plan on making this, make sure your driver can handle it.

Since you’re looking for feedback, the only thing I can say without seeing the CAD is that I would use a snap ring to hold the large cluster gear in place instead of the screw + washer. Granted, you might not have the capability to machine a groove, but I generally prefer snap rings since they’re lighter and don’t have the possibility of self-loosening.

Hi thanks for the responses I published the CAD here

I am not sure how thick should the webbing be my webbing is 4 mm wide and the plates are 5 mm thick. when we will have our new CNC router setup we will start testing with the pocketing

I normally do approximately 6mm wide by 6mm thick webbing. Especially if this is your first custom gearbox like this, compromising with thinner webs may not be a good idea.

Not sure if you’ve seen our 2018 gearboxes but they look to be pretty similar. Something we did was instead of webbing the plate for vents we pocketed out the area around the motor mounts to create a raised boss to space the motor from the plate. IMO it allowed for better airflow especially once you get to thicker plates. Conveniently it’s also quicker to machine since you don’t need to move to a tiny end mill to get sharp corners.


The pocketing ended up reducing the plate to about 5mm thick. This was a little too thin in our experience even though our design was a little better supported than yours. We had some issues where the plate would bend making the mesh uneven and causing premature pinion wear.
In the future we’d probably want to start with 3/8 in material but remove more of it leaving thicker ribs.

The other thing I’d note is if your designing a 32DP gearbox where the motors fully surround the gear instead of just being on one side you should add a little bit of distance to your C-C especially if your machine isn’t capable of holding high tolerances. We didn’t add any distance to our C-C which I think would of been fine in a single motor gearbox since there’s some slop in the bearing and shaft that ends up increasing the CC. When the motors surround the gears it ends up over constraining the mesh and causing premature wear. +.001 - +.003 should be fine.