Quote:
Originally Posted by Knufire
tl;dr, it's not easy.
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Oh hey that looks familiar. One correction is that the sprockets were elevator not wheel sprockets. It wasn't the easiest thing we've done but it wasn't the hardest with the hours of CAD work paying off with a relatively painless assembly.
3467 was feeling inspired by our new manual mill in our shop we designed a robot that required our drivebase and elevator gearboxes to take up little to no space.
We packaged it all in 2" x 2" x .125" wall tubing. We could have used 1.5" x 2" but opted for the 2" since it made mounting up easier with the Vexpro tubing and a little more room to work with. We used 18T sprockets for 25 chain and spaced out the bearings to be C-C however something in the math was wrong so the chains had a little more slack compared to our C-C we ran with 35 chain the year before but since it was inside the tube and impossible to come off we didn't bother adjusting it. We may have designed it to be less than C-C I'm not sure. As we found out the slack was a nice feature since the chain was easier to install.
Overall it was a very nice setup and we loved this assembly. Each module was responsible for driving the wheels and providing power to our elevator with a duplicate module on the opposite side and an axle higher up that connected the two sides of the elevator to keep them in sync.
IIRC after these were assembled we only touched them once on the practice bot in Week 6 due to one of the axles getting pushed out while adjusting one of the sprockets on the outside for the elevator. It took a while to get the spacers and sprocket back in line since the superglue had done its job during assembly and had broken away so we had three floating pieces inside the tube on each axle. Not ideal but it worked for what we needed and unless you pulled the axles out the inside was solid. After that minor mistake we never had an issue on two robots.
Some pictures of the assembly are available
here. Weight as shown fully assembled minus wheels and encoders was 16.5lbs. We had plans to lighten the large gears but always found the weight in other places.
I would highly recommend you try this out at
least once in the pre-season. Our original plan was to machine these on a manual bridgeport but we needed 5 of these made and holding those tolerances on one would have been difficult so I brought them to work and CNCed them. It was our first time trying a lot of things this year for the first time IN season which is typically frowned upon but we worked through a lot of CAD revisions until we were happy. Consider the impact running chain inside your tube has on how you can mount to your frame. Since ours was only running to our elevator it wasn't spanning the full length of the tube so we had an easier time mounting cross members in the back and our vertical assemblies needed to be re-thought a few times.
If you have any questions feel free to PM
echin the student who designed it &
JamesB3467 did the gearboxes. Huge thank you to 118 for sharing some insight into their design that inspired our students to tackle something harder! Also to Vexpro for their great lineup of products making complicated mechanisms easier for teams to try.
Also for getting around the issue of adding a drop into your drive, Colsons are pretty easy to throw on a lathe and shave down to size with the right cutting tool. We did this in 2014 after we accidentally designed our drivebase with no drop.
To the OP: Looks good nice to see you trying something new, hope it works out for you guys. Something to consider, what is that outer plate doing for your drive that the tube/mounting surface can't provide? For some designs you might need it, others its a nice way to eliminate a part and shave some weight out of the base. Just a thought.