Frame Material

[Tristan Lall]

It's going to come down to the corners, in terms of structural strength and stiffness. What methods of joining and securing the corners are available to you? (Components for joining corners include rivets, tubing inserts, bolts, welds, gussets, 80/20 hardware, etc.; tell us what you can use.)

Also, what's your budget for the frame (roughly), and do you have any of the specialized tools needed for any of the above joinery techniques? Some methods will have higher costs, obviously.

What wall thicknesses of tubing did you have in mind? Conventionally, most teams that use it use either 0.050 in, 0.063 in or 0.125 in wall thicknesses. This decision will depend somewhat on what you want to do with the frame, and what needs to be mounted to it. This decision will also have a substantial impact on the robot weights.

The kit frame is a solid option, if you're interested in making use of its predefined mounting positions. It's somewhat less good if you have complicated machining in mind, or need something other than Ø0.25 in holes. The corner gussets are quite strong as well (but heavy).

As for bumpers, they're 0.75 in of plywood—so take the opportunity to make them structural. When done right, the bumpers are often stronger than the frame, and are very difficult to break. Use hardwood plywood (birch, maple, etc.) with relatively smooth surfaces; it's more expensive, but you can often get a good deal on a partial sheet in the offcut section of the lumberyard. You might as well get the lumberyard to cut it for you into 5.00 in tall strips (but insist that they guarantee the accuracy of the cut—don't buy it until you're satisfied that they're correctly-sized).

Of course, the bumpers need to be quickly removable from the frame, so design a robust, yet simple mounting system. Many teams will use threaded inserts (e.g. T-nuts) with headless bolts drilled for strong cotter pins. If designed carefully, you can add substantial stiffness to the frame, and still be able to pull it apart in seconds.

As a guideline that will save you time when rushing to your next match, or when participating in inspection, your bumpers should each be removable by one person in ten seconds.