pic: 2823 Offseason WCD Test Chassis

Team 2823 WCD Chain-in-tube chassis. This is out first time making a chassis so any feedback would be helpful.

At first glance I thought you used some kind of staple to hold the frame together.

In any case, Looks nice. Good job!

Nice job for your first attempt! A few minor points to make the system better.

First, if your chains were to break you would need to remove either your front or rear rail to access them. As of now that may not seem like a big deal, but once you have electronics and a superstructure added to your robot it will become increasingly more difficult. Take a look at the chassis on our 2014 robot, we use internal belts, and we leave the tube ends open to have access.

Secondly, have you considered using gusset plates on the top of your rails to connect them instead of the aluminum angle? You could use VEX pro parts, or make your own. You could just match drill them if you do not have access to a mill. I think that a gusset plate and rivets will create a stronger connection than the angle in the corners.

I hope this helps!

Looks great, not bad for a first time chassis build.

My only question is, why are you using the WCP SS Gearbox in the WCD configuration when you’re doing chain-in-tube? Using the standard configuration would save you almost an inch of space on each gearbox (and also reduce gearbox cantilevering due to motor weight).

One of the things that I noticed is your belly pan appears to be attached directly to the bottom of your rails. We did this a couple of times and the screws eventually came loose and the belly pan dropped out of the bottom.

I would make sure that you have plenty of support especially around the battery. You could possibly attach some angle brackets (like in your corners) and mount the belly pan to them.

Also, does your cutout for the gearboxes have enough clearance to remove them without dropping the pan out?

It is really difficult to drop a gearbox out of the bottom of a belly pan, by the time that you pull the axle out of the tube you would need to remove most if not all of the center section of the belly pan. You really need a custom interface between the gearbox and the output shaft for that to work.

We’ve been attaching our belly pan directly to the bottom of our rails for a few years now and have never had a problem.

Same. We use rivets to prevent the issue of screws pulling out.
As far as supporting the batery goes, 1x1x1/16" aluminum angle on the top and bottom of the battery have worked for us in the past.

What does your belt path look like inside the tube? I get that chains have the dual sprocket but I don’t know how to do it with belts without doing something really strange.

You could use two 9mm belts within the tube. If you routed belts like you have pictured, you’d want to be careful to make the sides mirror images, as the system you show would be more efficient at accelerating to the right than the left, as the tensioners would take up relatively slack segments to the right, but tight segments when accelerating to the left.

That image of the belt path that you found is from our 2011 robot, it was our first attempt at a belt drive. It skipped teeth and did not work well.

We redesigned the system in 2012. We use 1 1/2" x 3" Tube - we use two 15mm belts in the same path that chain would take. We make custom pulleys that fit inside the tube. We buy the pulley stock from SDP/SI The pulleys are 1.200" long with a 1/2 hex broach. We don’t need a flange because the tube keeps the belts on the pulley fine. We also offset our axle bearings with .125 plate so that the inside of the bearing is flush with the inside of the tube.

Keeping the ends of your tubes open is a plus. If not, consider attaching the front/back tubes & bellypan with bolts for cleaner access. Rivets can be faster to drill out and replace compared to a bolt/nut but having the variable of aluminum shavings flying around your robot in the middle of a crisis repair isn’t worth the few seconds in most cases. 3467 ran a Chain in Tube running our elevator last year (the layout was identical to a 6wd setup like this one) and having the ends open made the single repair/adjustment we made to the chains after assembly not as painful. Someone (cough me cough) accidentally pulled the center output shaft on the practice robot.

If we end up using a design like this in competition we will defiantly have the ends open. We broke a master link while playing with it today and learned our lesson the hard way. I wasn’t too hard to fix though.

When we were looking at gearboxes we saw that it was thinner. When we got it there were only the long standoffs. Do you order shorter pieces separately? It seems to be working fine but a shorter gearbox would be nice.

Did you consider rivnuts or other captive nuts? When combined with a cordless screwdriver and the appropriate bit, this could be just as quick to remove and replace as a rivet – without the shavings and need to keep a big stock of fasteners in the pit.

The problem I see is, where do you install the RivNuts in the tube to where you can still remove and replace the chassis rail internals without running into the RivNuts? If it were a rivet, you just drill out the rivet to remove the tube, which also removes the obstruction in the tube.

That depends on the placement of the rivnuts, really, although you make a good point; double sprockets would definitely give you trouble.