For the 2 CIM ballshifter, my understanding is that some longer standoffs between the casing and the third stage plate will give space for sprockets to sit and allow us to use this gearbox for WCD. The tricky part is that the standoffs get in the way of the chain and we can’t find an easy solution for that besides making some more complex custom parts.
Anyone else done this and willing to give advice?
How are you mounting it? I believe the gearbox can be mounted straight up and down, but can also be mounted turned on it’s side. Its possible that the chain will clear in a different mounting orientation. I’m just speculating however, so hopefully someone with practical experience can chime in. You could also contact VEX customer support directly.
Edit: Follow up question: what size sprocket are trying to use and for what size chain?
I looked into this a few years ago, and again last offseason and the only way is to make a custom plate and standoffs. *(https://imgur.com/a/P6AqmfT) You have to make a plate with different standoff locations, that bolts to the existing ones. It shouldn’t be that hard but if we ever decide to do a shifting chassis we would just buy the 3 CIM for the extra spread options.
The location of the bearing hole when using 3 stages makes it that the gear box would be very close, if not touching the ground.*
Last year we chose to mount our chain and sprocket on the outside of the rails. We did this because we wanted our elevator rails to mount flush on the chassis rail with no chain in the way. There are a few tradeoffs.
1.) The leverage point on the axle moves out ~1" from the rail. This was a non issue.
2.) The rails are closer in on the robot. for us this was an advantage for the elevator mounting.
3.) It can be harder to mount the bumpers, since you now have chain on the outside of the chassis rail.
I would recommend just using the 3-cim ballshifter and mounting only 2 cims to it. It’s actually cheaper than using the 2-cim shifter, and far easier to mount.
We used these in 2017, and took the “make a complex part” route. We built a bracket that interfaces with the versablocks and has moved standoff locations. We ended up drilling two holes in the plastic case for two of the new standoffs. It worked fine. We used the 2CIM gearbox instead of the 3CIM gearbox because of the odd size rules in 2017, I’d prefer to use the 3CIM gearbox with just 2 CIMs mounted, it’s easier to interface to.
What we did is cantilever the whole gearbox, off the third stage plate, to make room for our pulley and the other pulley is in the tube for the far front wheel. It was really simple, but the only problem we ran into the whole season with the set-up was putting the gearbox assemblies in the robot because the thing was so long, the motors had about 2-3 inches in between them.
Also, if you want to look closer, here is the GrabCAD link to the whole robot CAD.
Edit: Second attachment shows what holes we used to mount it. The bottom bolts just tap into the hex shaft spacer.
