Arm swings when turning, how to brace it?

[jimwick]

Our arm twists also, it is pretty light.

What we found out in many hours of practice driving is that it didn't matter; it twisted but didn't break. i was sure it would break, but it didn't.

What we are doing is making sure that the arm and gamepiece is in "stow" position whenever we travel. That will also somewhat protect it from entanglement with other arms.

we are not sure whether our arm can take the rough and tumble of the competition. we made plenty of spare parts!

jim wick

[MrForbes]

Our arm twisted a bunch the first time we built it, we found the weak points and redesigned them, and now it twists a bit, but it's acceptable.

But we used tubular materials for the long parts.

If you can use the robot, and it doesn't get damaged by things moving around, then some deflection is acceptable.

Did you ever sit in an airliner and watch the wings bounce up and down?

[Ether]

Originally Posted by squirrel

Did you ever sit in an airliner and watch the wings bounce up and down?

Have you ever flown in a 707 and sat in a window seat? The wings move so much it looks like they're flapping like a bird's wings.

[MrForbes]

heh....i'm not THAT old. My first ride was in a 737 in the late 70s

[Dad1279]

You can also find 1x1 thinner than 1/16th at places that sell sign materials.

We buy alumalite & light aluminum tubing from http://www.harborsales.net/Default.aspx
tubing here: http://www.harborsales.net/tabid/130...oductTypeId=27

[Ether]

Originally Posted by squirrel

heh....i'm not THAT old.

Thanks a lot :-(

[MCahoon]

Originally Posted by squirrel

Ace, Sutherland's, Lowe's, and Home Depot. Although I have to double check Lowe's, as I didn't buy it there this year.

From my experience, the 1x1 I get at Home Depot here is 1/20 in. wall. Light for an arm by itself, but when used to stiffen it could be sufficient.

[MrForbes]

Yes, thanks for the correction. I bought a stick of it there and noticed it said 1/20, but forgot until you just reminded me.

[Ian Curtis]

Originally Posted by MCahoon

From my experience, the 1x1 I get at Home Depot here is 1/20 in. wall. Light for an arm by itself, but when used to stiffen it could be sufficient.

It likely is. When I took Aero Structures last semester, one of our homework assignments was meant to drive home the fact that a closed section (like a tube with a square or circular cross section) is significantly more resistant to twist than an open section (imagine a tube after you've run a sawzall down one side).

You can show that for the same stress a circular thin walled closed structure (like a length of tubing) can carry 60x the torque of the equivalent structure with a slit down one side.

In layman's terms, you get about 60x less twist once you close the structure. Tubing is your friend.