775 Gearbox for WCD

My team is planning on designing a wcd during the offseason with a 2-speed gearbox with 4 775’s for the first time, and we were looking for feedback on our current design.


Any feedback is greatly appreciated.

Looks pretty nifty! I haven’t had time to go super far into it, but I do have a few questions:

  1. Why use the shaft collars on the cluster shaft? They can and will work themselves loose over time (probably midway into elims).
  2. What is that fancy bearing block thing for on the ballshifting shaft?
  3. Why the final 1:1 gear stage?
  4. How does it attach to your siderails?
    The main structural problem I saw was the use of a lightened 32dp gear instead of a steel one for the first stage. Given that you’re putting 4 775s into it, steel is a lot safer. Apart from that, this looks like a really good design. The lightening is tasteful, if conservative, and everything looks pretty solid.

This a a great looking gearbox however I would personally try and take some more metal out of the 775 mounting plate to reduce weight. I don’t know if this would be strong enough but if you used something similar to a super shifter shaft to adjust from the input of the 775’s into the countershaft with with you main reductions you could save weight and skip the second 80 tooth and 20 tooth gear. I might also move the 20 tooth to the countershaft and so that way you can drive from the 80 tooth pinion to the countershaft. If you did that you could shrink the size of your gear box quite a bit by condensing it. That may also make allow you to run bolts through your standoff into the side rail constraining it to your robot. I may be totally wrong but at first glance that is what I might change. It is really a cool gearbox and that it is a great summer project.

I have updated the model to change the shaft collars to e-clips.


The bearing block is so there can be a bearing mounted on the shifting shaft. My team has no experience with the use of a ball shifter, and my only knowledge of its workings is from dissecting a CAD model from a VEX pro gearbox. They showed a bearing mounted in that position, and we figured better safe than sorry.

The final 1:1 stage is so when the gearbox is mounted to the 1x2, the output shaft can be mounted in the middle, and nothing hangs below the bottom plane of the 1x2 in order to allow a belly pan to extend under the gearbox offering additional protection from sag.

I’ve added two mounting points totaling up to four mount points for the gearbox onto the base, depicted in the attached image in the grabcad page. Similar .5 in diameter standoffs will be used to attach the plates of the gearbox together will be used to mount the gearbox to the base.

I am unfamiliar with Andy Mark’s super shifter, and was wondering if you could explain what you mean when utilizing a super shifter shaft. Condensing the gearbox would be very useful to us, as we are cutting it close with mounting electronics with our current system and robot.

I have updated the gearbox to change the shaft collars to e-clips.


The bearing block is to allow a bearing to be mounted to the shifting shaft. My team has no experience with two-speed gearboxes, so the extent of my knowledge is dissecting the CAD model for a VEX pro gearbox. The model depicts a bearing mounted on the shaft in that location, so we added the bearing mount in order to be safe.

The 1:1 gearing is to move the output shaft down so when it is mounted in the middle of a 1x2, there is nothing below the bottom plane of the 1x2. This will allow for the extension of a belly pan under the gearbox which will mitigate stress on the mounting joints from sag.

I added two mounting points on the gearbox to bring the total mounting points to 4. There is a picture with the mounting holes circled in the new grabcad. 1/2 in standoffs similar to the ones used to connect the plates will be used to mount the gearbox to the base.

I am unfamiliar with Andy Mark’s super shifter, so I do not know what you mean when you say to use the super shifter shaft to condense the gearbox. Shrinking the size however would be highly beneficial because out current electronics system would barely fit if we used the new gearboxes. Any further explanation or tips on reducing the overall size will always be appreciated.

Another note, I switched out the aluminum 32 dp gears to steel per the recommendation.

Thanks to both of you for your advice!

How much more would it weigh if you used the plate with the motors on it for both sides?

On the 1:1 output shaft, you do not have it anchored to anything. The robot load will be exerted on that shaft and the quarter inch plate, and in my opinion it will not hold up. You also added a shaft collar to the end of it, which will come loose. This season my team decided to use shaft collars, so we can mount greyhill encoders to the shaft, and they constantly kept getting loose. C/E clips are nice and all but require precise machining, in my opinion using a bolt and washer on the end works better, and makes the manufacturing process a lot faster. My team only has a cheap hobbyist lathe, but if your team has a proper lathe or has experience with C/E clips it is completely up to you.

Paulius Pace