pic: FRC 1771 Concept Drivetrain

After my last drivetrain I decided I would post up something a bit less controversial. Well not really but I have taken a new approach to design. we are sponsored by a sheet metal shop so it made since to design a robot that would utilize their machinery so this is my take on that. The drive module are made from laser cut and bent 1/8" thick aluminum. It is held together by Delrin standoffs and bolts to minimize weight. The wheels are 6" diameter custom machined from UHMW plastic and treaded with roughtop conveyor belt. This uses the guts from andymark shifters but packaged into the frame rail to save weight and a little bit of space. Total weight I am shooting for is between 35 and 40lbs depending on chain although currently everything pictured is 34lbs. Ground clearance is excellent and it has a 55 degree approach and departure angle. The super structure will mount to the center tubes which we can move basically anywhere on the drive modules with different holes. Let me know if you have any questions or comments.

Also I have one question. Does anyone have experience with .1" thick aluminum in this use and would it hold up instead of .125" thick?

Any particular reason you are bending the edges of the side plates outwards instead of inwards? Last year we built similar side modules and found that by bending the tabs inward on the sides we could just flush mount the bumpers to the sides of the bot. Which was really easy and nice.

I would also recomend that you don’t cut weight out of the pieces in front and back of the drive side modules. We seriously bent up the 1/8th inch metal right there on our bot, even without any weight taken out of it and a 1 inch piece of wood bolted in front of it to absorb the shock.

Another good way to attach superstructures to the frame is by making a big sheet metal bracket and bolting that to the top of your two drive sides and back side. Eg

I actually spent a lot of time looking at your robot from this past season when designing this. The main reason I have the bends going outwards is so that it is easier to work on things on the inside although I don’t know how much difference it would make looking back on it. Maybe I’ll draw up one reversed and see how it looks. Also on the front and back piece would you maybe recommend switching to 1/4" thick plate. The weight gain wouldn’t be too substantial since it’s a small piece, or maybe even switch to a composite like fiberglass, something that wouldn’t bend as much.

We never had an issue with it being faced inwards. It was a tiny bit harder to get a wrench in there to tighten our chain tensioner, but not by anything significant.

I would personally recomend just putting a nice piece of 1 inch thick solid wood up there in front of the 1/8th inch thick metal. Our sheet metal sponsor told us that the maximum thickness aluminum they could laser is 3/16, and that they prefer 1/8th because the cutting time is a lot shorter. We attached a piece of 1 inch thick wood up front, and that reduced the damage to our frame by a significant amount. Our frame only got bent up where the wood wasn’t. The wood is pretty light, and absorbs shock nicely. Our wood is missing quite a number of chunks, and all the left corner is very well rounded off, but the metal behind it held up well.

I am assuming you did not have bumpers in the front where the metal was being bent? I know of a couple teams (233) who used even thinner aluminum sheet in front and back and they didn’t bent anything, of course they had bumpers around the whole thing. Bumpers also help a lot more than just a piece of wood. As far as reversing the plates, I will look into that more. No matter the orientation, I am still planning on having brackets for the bumpers to slide into on top so we don’t have to deal with bolts through the drive module, so really with the bend facing in or out it is the same.

Correct. We couldn’t put bumpers up there because we wouldn’t be able to get close enough to the ball to grab it and stay in the 80 " rule.

And our driver would consistently end up ramming the bot into the corner of the center divide at full speed at least once per match.

1/4" plate can be hard to mate with sheet metal. If you’re working with a sheet metal house there should be spot weld ability. I you need more local material you can make doubler plates and spot weld them to the main plates. This is particularly useful if you needed more material for mounting features or local twist/bend resistance.

Thanks everyone for the ideas. I think if we have a situation where we can’t use bumpers in the front or rear I will use 1/4" thick lexan for the endcaps. Lexan can take a ton of punishment and won’t permanently bend. Also it will be a relatively light weight solution to the problem. Although if at all possible I will definitely push for a design that lets us use bumpers.