pic: 6WD Riveted Frame Development

[Mike Nawrot]

Originally Posted by squirrel

Using fiberglass for the main frame members is really nice....no dents....

Fiberglass is a great material for this application. Just a few things to keep in mind while working with it:

1. Gloves. Fiberglass dust can itch and sting if it gets in your skin.
2. Goggles (a must no matter what you're doing)
3. Dust mask/vacuum. Fiberglass dust likes to float around in the air if you don't have a vacuum held to whatever you're machining. Inhaling the stuff is not recommended..
4. Pay attention to what kind of stresses you're putting on the fiber glass. We used fiberglass for our ball holding mechanism frame this year, and in the scheme of things, it worked great. The one issue we ran into with it (apart from the constant irritation of the fiberglass dust), was the fibrous nature of the material. Since fiberglass is a series of glass fibers held together by an epoxy, drilling holes in the material leaves exposed fiber ends, allowing the material to be pulled apart. This caused some failures in our design, resulting in tubing that was split down the middle. There were two fixes to the problem that we looked into. The first (and heavier solution) was to put reinforcing plastic inserts into the tubing to reduce the stress on the holes. The second (and less precise) solution was to epoxy any machined edges to reseal the fiber ends. Of course, this issue is only a problem under certain conditions. We had plenty of machined connections on the fiberglass that held up fine through the whole season. The key is predicting and observing the stresses that the parts will be under, and designing accordingly.

As for rivets..

The super structure for our ball gathering and shooting mechanism in 2006 was 1/8" aluminum with 1/8" rivets. Only after two regionals, championships, and two off seasons of constant abuse and the robot flipping over onto the super structure did the rivets start to come out. So riveting is definately a viable solution. As for maintenance, pop rivets are usually pretty easy to remove by simply drilling them out with a drill of the same diameter (i.e. 1/8" rivets removed with 1/8" drill bit) and using the hole from the shank as a center.

When using aluminum, I find that it's good practice to use aluminum rivets. Since the steel is harder and generally stronger than aluminum (except for the rare cases like 7068), using a steel rivet can mar the aluminum. 3/16" aluminum rivets should be sufficient for this design, especially with the number that you appear to be using. I could be wrong though, as I've never actually constructed a riveted drive train. If you decide to use steel rivets, use washers between the expanding part of the rivet and the aluminum to distribute the force over a greater area.