[dtengineering]

I know that you are going to test this design before you use it, so I'm prepared to be proven wrong, but my "gut sense" is that this design may be prone to failure due to the repeated hammering on the axle as the motors shift from forwards to reverse.

Keeping the sprocket as close to the wood as possible should minimize the effect of torque, but I think you could do that even better by gluing a second thickness of plywood around the axle hole. In fact, I would be tempted to drop down to 1/2" plywood, then reinforce the axle mounts by gluing a piece to each side to help distribute the stress, but more importantly increase the lever arm between the t-nut and the nut.

In fact, I would even go so far as to suggest that laminating up the side rail out of thinner pieces of plywood would allow you to control the cross section, weight and stiffness of the side rail along the length of the robot... however that might be getting away from the "quick and easy" aspect of this design.

I would also be tempted to consider replacing the t-nut with something larger and, perhaps, a bit stiffer. I'm thinking of a tapped aluminum bushing in the shape of a t-nut, but with 1/8" walls and flange. The bushing could be epoxied in to the wood (knurl the outside for a great grip) and then the flange could be screwed in to the plywood as well. Again, this gets away from the "quick and easy" and requires access to a lathe and tap a bit, but even though I really like to see wood used in designs, I've got some concerns about whether the design proposed here will be able to handle repeated cycling and impacts.

On the other hand... I may be underestimating how well this set up will distribute the load. Good luck with the testing!

Jason