So I was working on some CAD designs of an x-drive for Change Up and I came across an issue that I honestly did not even foresee to be a problem.
as you can see in this image, the ball slightly contacts the motors here when it is in the middle of the two front motors. This is at 17.5" wide, which is what concerns me.
I know that 210Y released a reveal of an x-drive bot for this year, and it seems like they didn’t have this issue.
Personally, I’d like to trim as much width off the robot as possible, while still using an x-drive. Is this just something funky with the CAD or is there a mechanical deficiency in my design? If neither, any ideas on a workaround (maybe a different place for a motor mount)?
Btw, I’m planning to make a snailbot if that helps at all.
I think that the ball is tall enough that it’s widest point is above the top of the motor. (i.e. Look at your drive from the front, with the ball aligned with the ground, as it would be in real life. I suspect that the ball does not actually intersect the motors.)
If the ball really does intersect the motors, though, I’d sugest reducing the distance between the side channels from 3 holes to 2 (and compensating by adjusting the angled channels). That should provide some extra space.
How wide is the middle C-Channel?
It’s a ball so u can’t look at it from the top. If u look at the front view the motors actually don’t hit the ball. If u use lexan, u can make a ramp and push the ball up a bit higher so that u can make a slightly smaller chassis. In my testing I could make an x drive 16 inches wide minimum
Also I think u might have made the wheel spacing very tight to increase the space. U don’t need to make it that tight. I believe I was able to do:
And still have some wiggle room for the wheel. Ps all the spacers were 0.25 inches
When I started my cad with an x-drive this year, I ran into the same problem. After some simple geometry though, It is quite obvious that if left the way you have it now, the ball should easily pass through the said gap. My suggestion would be to add a guide spanning between the motors (parallel to the sides of the drive base) so the ball does not become lodged in one of the spaces between the motors. Good luck! Hope this helped!
Why not use smaller omni wheels with motors geared higher?
My understanding is that there are three sizes of wheels and several internal motor gearing kits. I don’t have the speed charts in front of me, but idk.
H5 comes to mind, both my solution and Andrew Remmers:
I was doing some crazy stuff like making square tubing out of spliced up c-chan and milled spacers out of the polycarbonate block, and fully abusing the aluminum plate we had in VEX U. Wouldn’t suggest that this exact option is available to you. In general though, pushing the wheels to the far corners is the answer, so start there and work back.
Also cantilevering the wheels. Esp with the 1/4" shafting. Although not doing that has advantages too.
Gearing can with some additional slop help push the motor back a bit. Looks like you only need to pickup a little space on either side.
God the V5 motors are large.
I mainly wanted to use 4” wheels because 4” wheels on an x drive already bring u to the equivalent of ~280 rpm. Also, the main problem with the chassis is that the balls are hitting the motors, but by adding gearing, you are pushing the motor inward. Though it may be a little lower, the ball will probably end up hitting the motors anyway.
There was a team one year that had used chain to move the motors up and over the wheels freeing up the space. (motor flips from being inside the space to the outside). I would have bet a pizza that it was your design?
Most of my VRC was pre-strong-chain. I think that came out during the Round Up season? Anyway I never used the large chain for whatever reason. I’m not a fan of slop in wheels.
Ok, so there is a pizza up for grabs here then
Anyone want to put a hand up and say “Hey Foster, we did that, send the pizza to …”
It was pretty simple there was a structure over the wheel and there was a chain that ran down the inside to a sprocket on the wheel. The motor was close to the wheel so there wasn’t a lot of chain between the two sprockets. So some “slop” in the base, but not a lot. I sort of remembering that it was on those green rubber shocks to help with the alignment.
stacking motors above your wheels is a valid option to save space, but you might not need to. since the game pieces are balls, you can have your motors be closer than 6.5" together and still have clearance, if the motors are low enough to the ground, because of the curvature of the ball.
Here are some photos of 8768A’s Nothing but Net robot which employed this technique. This probably isn’t the robot you’re thinking of though, I don’t remember sharing any photos of it at the time.
Overall, this setup worked okay but not great; probably would’ve been a lot better if we’d used larger sprockets and taken care not to over-tension the chain.
Instead of changing the motor setup or spacing, you could simple have the ball run up a ramp over it through the use of bent lexan , standoffs, hinges, or gussets.
No not them, the robot had bigger sprockets. Those tiny ones were the bane of splitting the chain with the tight turn radius.
OTOH, if nobody else shows up, the pizza is 8768A’s, thanks for the picture!