Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

1/8" wall for drivetrain, 1/16" wall for superstructure and bumper rails.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

I hope that 60 lbs includes all motors and additional parts. Our superstructure frame was about 8lbs. I just can't see the argument for steel tubing (or steel anything other than gears, chains, bearings, and bolts) in FRC.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

All motors and additional parts were bagged and tagged. An 8lb superstructure? What did you use? What did it look like? Was it strong enough?

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

I have a simple question about the construction of a "WCD" system. Having no experience with these, yet, we want to learn from other's experience to help minimize the normal error associated with trying something new.

I see mention of using "bearing blocks" quite often when building WCD's. It is necessary? Couldn't the bearing's be pressed directly onto the walls of the tubes?

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

Team 48 has done this the past two years with no issues. Instead of including movable bearing blocks to tension the chain you have to design in additional tensioner. We have just used 1" round Delrin(Acetyl Resin) with a hole drilled off center with great success, turn the cam against the chain and then tighten down a bolt to hold the cam in place.

Here are the CAD files for our 2011 robot. The bearings are pressed into the frame members as discussed, but the delrin chain tensioners aren't included. They are more of a install as needed device. You may also want to find the equations to calculate chain lengths based on an even number of links, this should lessen the need for tenioning and half links.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

I see two main purposes of the bearing blocks. One, they allow for adjustable chain tension by sliding back and forth. And then they also support the axle more. However, we did run an 6WD drive this year with another set of wheels in the front for total 8 wheels. The set in the front had bearings pressed into the frame. However, since we were running a drop center they were raised above the ground while we were driving, and not really taking on any load.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

This is the only photo I have online right now. It's primarily 1x2x1/16 6061 rectangular tubing, with some 1x1x1/16. The superstructure is comprised of the four 1x2 legs, the 1x2 horizontal brace across the top back, the two 1x2 shooter wheel/hood supports, and the four 1x1 roller supports and gusset braces. About 8lbs total for the framework, plus all the weight in motors, polycarb, etc. The front deployable bridge/intake device is not part of the superstructure.

The base is 1x2x1/8 for the sides, back, and front, with 1x1x1/16 and 0.5x0.5x1/16 pieces for the bumper mounting.

The whole thing is plenty strong. We have tons of fun using the front triangles to ramp it and jump it over the barrier, or speed bumps in parking lots. It catches air nicely and lands pretty level, with a slight bounce from the pneumatic tires.

Based on my experiences flexing back warped frames after welding, I wouldn't go to 1/16 wall for the base frame.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

Those bearing blocks on many wcd's are really nice, and if we had the resources, we might do it that way, but they are not necessary. We also build ours like Mr Reed from team 48 explained. I use one of those step bits to drill the 1.125 holes for the bearings. they make a real nice hole. It's not a super tight fit, but a little loctite takes care of that. The real trick is getting them perfectly across from each other.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

If you are abandoning a sliding bearing block, absolutely. We've done this for two years without issue.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

What do you do for chain tensioning? Sliding bearing blocks are one of the cleanest ways of tensioning chain that we've discovered. I suppose you could do exact distances, and hope that your chain is perfectly tensioned and doesn't stretch enough to become a problem, but I wouldn't want a drive train without control over my chain. That's what happened last year basically (and every preceding year), and it was really terrible. We thought breaking chains was a normal thing during operation.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

We don't use chain, we use timing belt. That's the only reason we can get away with it, since timing belt does not stretch.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

We're probably going to try timing belt for next year, so that would be an interesting thing to test. Do you weld anything near your drive trains (or would you worry about warping ruining your tension if you did)?

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

Hey Bill! This was our first year of doing a WCD. We have been using 1.75" x 0.75" Aluminum C-Channel for so long, we decided to stick with it and use it for a WCD setup. We did two pairs of C-Channel facing inward and milled center bearing holes for 1/2" hex bearings with a 1/8" drop. Then we milled slots on the ends to accomodate either 4" wheels or 6" wheels (4" was used in competition). We made bearing blocks out of chunks of 0.5" x 1.5" aluminum stock. With a tapped hole on the ends, we could then tension the chain easily. The setup worked perfectly and we never once had to touch the drive system.

The downside of our approach of using 4 lengths of C-Channel instead of the classic WCD 2x1 was weight. Our chassis was definitely heavier than most WCDs. BUT we knew this and since our approach to the game this year was to carry another robot on top of us, we decided to play it safe and go with a more robust chassis. Our robot drive system and chassis was tested up to 400 lbs including bridge climbing and balancing.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

I'll give the basic run down of our chassis.

We use 3x1.5" 1/8" wall AL tube for the drive rails and 1x1x1/8" tube for cross supports and a 1/16" belly pan. We start by riveting on the belly pan and "framing gussets" to hold the assembly in the proper orientation for our welder. As he goes, he removes the gussets, but welds the belly pan to the chassis.

Next we put the belts in the tube. We put the belt around the pulley and feed the pulley down the tube using gravity (the chassis rails are tipped up.) This works because the pulleys are the exact same size as the inside of the tube and the belt is unable to slip off the side of the pulley. Once the center axle is placed in the center pulley (which already has both belts on it) the outside pulleys are next. Our bearing holes have a key which allows the axle to fit through. We slide the axle in the pulley and pull back on the axle until it is in the center of the bearing hole and slide the bearings on either side of the axle, securing it in place. This is the center to center location.

If you remember, the pulleys are the exact size of the tube, and the bearings are 1/4" long. This forces us to space the bearings out of the tube with a 1/8" spacer. On the ends, where the bearing holes are keyed, the spacers are riveted to the frame for extra support. We then use 4 10-32s and attach our gearboxes to the tapped holes in the frame.

This was the last time we touched our drivetrain the entire season. (We did do a dry run of the gearboxes before we took them apart to teflon the gears.)

Let me know if this doesn't make sense. We do plan on taking apart our drivetrain and putting it back together to make an instructional video. I also have been cleaning up our CAD model for publishing. Renders should be up in a few days and I will have a link for download.

Re: Do you have to use 2x1x1/8" tubing for a WCD?
 

What type of belt do you use? We have shredded the .2 pitch XL .4 wide belts we have used every time we ran them on a robot.