What do you think of this Shifter?

Hi
lately I’ve been working with my friends on new Shifter and chassis.
What do you think?
Do you have any recommendations tensioner ?
Thank you very much
https://grabcad.com/library/2630-off-season-project-drivetrain-and-shifter-1

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Can you provide some more specifics about it like gearing, weight, wheel diameter, size, etc.

edit: there is one obvious problem I can see and thats the over constraint on the output shaft with 3 bearings in a line you will probably kill the centre bearing and sap a lot of power out of your drivetrain as a result.

Currently the size of the chassis is
700X620
4 inch wheels (4 colson 2 omni)

It is not entirely clear to me the problem with bearings

For the center bearing you would need very precise machining and plate alignment for that bearing to lineup perfectly with the other 2 bearings on either end


Are you talking about this bearing?

yes

So how do you recommend doing this?

Just remove the bearing. There is not much load at that point and distance between the bearings is short enough that I wouldn’t be worried about the shaft bending.

One thing I don’t understand is these bolts?


Are they there to hold the bearing in? If this is the case I would just use flanged bearings pointed at each other with the step in the shaft holding the bearings in and capturing the shaft.
edit: here is a picture hopefully this conveys what I am trying to say better
using the bolts would work though.

other than those things I don’t see any major flaws in the design, you might be able to optimize the lightening a little but over all its a pretty good design.


Yes
They’re there to hold the bearing

A few things:

  • Your plates look over-lightened. Cutting all of those small pockets will save you very little weight and take up a lot of time. And some of the holes look very close together, which leaves little material to support the forces. If you think the plate unlightened is stronger and heavier than necessary, I’d recommend using a thinner plate or looking into different materials (nylon gearbox plates are starting to be adopted by more and more teams recently)
  • Using the motor mounting bolts as standoffs is going to make it a pain to replace a motor if the need arises. I would suggest using short bolts to the back plate for the motors (with clearance holes in the front plate for an allen key), and move the standoffs somewhere else
  • You never want to put a snap ring between two loads on a shaft. It creates a serious stress riser, which means your shaft will break much easier. See some analysis I did on the topic here
  • Is the top shaft for a PTO? If so, there’s nothing inherently wrong with that but in general I just don’t see the need nowadays. With unlimited numbers of any motor and very powerful motors that weigh less than a pound, the only real limit on how many motors you can have is the 16 PDP slots and the battery. For something like an endgame mechanism that would be powered by a PTO, it’s almost always lighter and easier to just use a separate motor and gearbox than to have to deal with the mechanical and programming complexities of a PTO
  • The small bolts retaining the bearing seem unnecessary. If you’re already tapping the shaft ends and using the bolt and washer method, you can constrain the bearings just by placing the flanges correctly. No need to drill and tap such tiny holes
  • The top shaft doesn’t look fully constrained (I don’t see anything stopping it from sliding out the front of the gearbox)
  • In your full chassis model, you seem to have one set of bolts attaching the gearbox to the tube that end in the middle of the tube, then another set of bolts from the front of the tube that don’t seem to be doing anything. Unless I’m missing something, it would make more sense to have one long set of bolts from the front of the tube that go all the way through, through the gearbox plate, and then get a nut behind the front gearbox plate.

Overall though, it looks like a good concept, and well packaged.

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To repeat what AMB said, the lightening pattern on the plates is the most noticeably suspect part of this assembly. Stress travels best along straight lines, so you’ll want to have the shortest possible path between the sources of loads (the bearing holes and some of the screw holes) and the mounting features. This gearbox has a similar layout to the WCP DS, so it may be worthwhile to take a peek at how they do it. Since the motor plate and the face plate are already different, it doesn’t make much sense to have the circular hole for the motor boss when you could instead run a rib to the edge.

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