Frame Drive

[Pault]

Originally Posted by Infinity2718

The shafts were placed in the center of the tubes for gear clearance, but with the incorrect ratios used from the above posts, things could be shifted. The first thing that comes to mind are a few gears external to the frame to give the correct ratio.

I realized that after I posted. You could always cut a hole into the bottom the tube and have the gear stick out.

[AndreaV]

I really like gears in the tube, but it adds two more shafts.
Prior to the vex 2014 product unveil I was playing around to see how compact I could make a 8wd. I came up with something very similar. It would be super light without the colson wheels, but I have a hard time giving them up. I like to think of this as colsons with cleats.

One of the design constraints was cost, I wanted to avoid using hex bearings as much as possible, and actually used halved 42 tooth AM kit bot pulleys for uber cheapness.
Half live axle, half dead axle, It uses a single width of 9mm belt to power the outer wheels on the outside of the frame, while running the inside wheels on two(yes, two!) direct driven shafts. With the single 12:60 reduction it is geared for 15fps, which even on 6 cims is too fast. a 11 tooth pinion would make it a slightly more manageable 13.75 fps.

[Deke]

Fantastic! I like how two different approaches end up in similar designs.

A comment about the hex bearings that is my opinion and I am sure will differ from person to person. Even though they cost a little more, they simplify assembly by removing the need for precision machining of shafts to get a good fit into the bearing. Round shafts would need a light press fit, or loctite, or maybe some sort of knurl to fit tight into the bearing. So the hex removes the need for any of those three things while providing slip fit and proper bearing usage. It's the never ending battle of cost versus benefit.

[Joseph Smith]

Last year my team integrated our gearboxes into our frame to save space in the middle of our robot for disc movement. We had 1.5"x3"x.125" aluminum tubing, and our drivetrain was west coast style. We took the gears and hardware from a Toughbox and built them into the tube, mounting the CIMs and some bearings to a single plate that was bolted onto the inside of the frame. The design worked and saved space, but we had some efficiency loss because the sides of the frame rail were not perfectly square, and it affected our gear spacing slightly. Also, maintenence was difficult on this design because there was no room to pull the CIMs off of the gearbox- however, this was due to other packaging in the robot, not the gearbox design. IMO if you can package this gearbox with the rest of your robot and you account for tolerance in the walls of the aluminum frame, this could work great.