Output Shaft for Bosch Seat Motor

Aloha everyone,

What output shafts are everyone using for the Bosch motor in the KoP? We don’t have the tools to machine it out properly to fit a hex shaft so we are looking for a solution that we are capable of. Thanks all!

There are some good options out there depending on what you are trying to do. WPI has released a guide here:

AndyMark sells an adapter here:

If your team is short on funds, you can buy this stock and attach to it. I don’t know how the tolerances shake down so if this was my game plan i would probably buy the over sized version and use a grinder to make it broach it’s own hole as it goes in.

For $10, its hard to go wrong with the AndyMark option.

That said, I recommend owning a 0.5" and 0.375 hex broach if you use hex products they will help even if you never use them for aluminum. 131 makes a lot of pulleys and rollers using PVC and Acetal. PVC for prototypes acetyl for competition. Our 2017 climber drum was even held onto the shaft using a broached acetyl part. When we took it apart there was no evidence of wear or damage to the plastic



Thank you. My only concern with that adaptor is that it only outputs on one end of the spline (we need two ends). Unfortunately, we are working with very basic tools so we can only do so much. I did notice the with 118’s Everybot that they used just a bolt through it - wondering how effective that is. We definitely need to start buying more specialty tools.

I caution you against using a bolt. Relying on friction alone for that interface is not likely to do what you want it to do.

What tools do you have available? What is your budget for a solution?

We tested the bolt method last weekend, and couldn’t get it tight enough for our little arm to hold the hatch cover. I’m not sure that it would ever be required to hold the cover on its own, but we went ahead and ordered the AndyMark adapters just in case. We plan to use two of them, cut off with a hacksaw so that the square parts meet in the middle of the motor. We will use limit switches to make sure that the motor stops trying to turn when the arm closes on the hatch and when it gets to its fully extended position.

1/4" square rod almost fits, it wouldn’t be too much trouble to use a file to make that work if you have any of that around, maybe in a variety set of axle keys?

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The Robonauts Everybot does use a bolt and a lock nut clamping around the motor. We intentionally chose a bolt over using the AndyMark option because we wanted the hatch mechanism to slip when it hits a hard stop so we did not need to use any position sensors or limit switches. This is essentially a slip clutch, if the mechanism slips too easily all you have to do is tighten the bolt.


We used the Andymark adapter last year. I don’t see a reason why you couldn’t cut two of them down and affix them together with Loctite.

As a caution, that little worm gear is nice, but it backdrives more than you think it will, and last year we broke a tooth three times on the plastic output gear using it on our intake lift. Depending on what you’re doing with it, you might want to consider using two of them facing opposite directions – this could fix your double-spline option and spread the load. (And if you want/need a spare or two, let me know via PM and we’ll ship them to you.)


A great idea on the Everybot to introduce a simple clutch type connection. Since it was mentioned that it was difficult to get tight enough some alternatives might be to 3D print something that acts as a failure point before destroying the gear. Just have a ready supply available that you would replace.

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We used a long through bolt on an early mock up and it worked fine for our needs. We made a few tiny wedges of hard plastic that when the nuts were tightened, the washers pushed them into the star points of the hub which helped a lot. Good luck!


We rigged up another of these motors today, and for the shaft we used 1/4" square rod which we ground down on the belt sander to 6mm. It fits snugly and wasn’t much at all that needed to come off of each of the four sides. On the output side we used a square file to turn a 1/4" drilled hole into a square for the non-ground end of the rod, and it fit well to turn our arm. Finally we used a die to put 5/16"-18 threads on the ends for nuts to hold the whole thing together. All in all it wasn’t a huge amount of work and at least in our preliminary testing seems to work great.

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Last year we used the seat motor for lifting our intake up and down. The motor was plenty strong but our shaft was not strong enough. We milled 1/2" steel hex down to the square shape which fits in the motor. The motor had no non axial movement on it because our shaft was fully supported by 1/2" hex bearings. We ended up twisting a few of the steel shafts where we milled it square, but did not breaking the plastic gears in the motor. So moral of the story is the motor is strong and needs a secure and strong way to attach it to the hex shaft. Make it as strong as you can…

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Adding my own story into this, we used a seat motor in 2017 to rotate an arm on our robot (little gear grabber). We used aluminum hex shaft from andymark and one of our sponsors/ mentors was able to use a 4 axis CNC I believe to create the entire 8 point interface. After our first event, we noticed a slight twist and decided to replace it, after that, we went through shafts like every match (not breaking but 3 or 4 complete twists). We replaced it with stainless steel and destroyed a gearbox. Going through purchase history after season, it turns out that the replacements shafts were made out of McMaster Carr 6061 1/2" Hex, which the original was AndyMark 7075 1/2" Hex. It made a huge difference in just alloy on whether we would have to replace the shaft once an event vs. once a match.

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Basic tools (hand drill, chop saw). Budget is fine, however, getting things to ship in time to where we live is difficult.

Thank you for the advice and offer!

Thanks all for the advice. We are going to try out a variety of solutions.