Arm swings when turning, how to brace it?

[HarveyAce]

Or arm is made of a single four foot aluminum c-channel with a fabricated 8020 bracket at the top to hold our window motors for the shoulder joint. the next stage is another three foot c-channel with the gripper on the end. we noticed in the little practice time we had that the channel tends to twist when we turn. Does anyone know of a way to brace the channel so that it won't twist? there are some pictures on the portal of our robot from last monday (team 3329) if that helps anyone. Thanks!

[J93Wagner]

Twist? In what way? Without knowing more about the problem, I can't help you. Sorry.

[HarveyAce]

the c-channel literally twists. like your ringing out a towel, just not as dramatic. like someone is holding the ends and trying to make a metallic twizzler out of it. hasn't had any damage yet, my concern is just that we don't want to enter a match like that.

[BJT]

a c channel or angle will always be easy to twist, if you could replace it with some kind of tube, round or square etc, it would be much more rigid.

[Tom Ore]

You may try bolting another C-channel over the open side of your existing C-channel. I assume your using the AndyMark C-channel from the kit of parts. There is another C-channel that fits over the AndyMark - maybe from IFI - someone can probably confirm this. This isn't an ideal fix but it may be easier than replacing the entire arm section.

[HarveyAce]

Actually we are using donated c-channel from the Trident Refit Facility here on Kings Bay Naval Base. They fabricated the channel from Aluminum sheet, as that is all they could do. other channel could be hard to fit into the grove as we have various screw and bolts going through the arm...

[sdcantrell56]

If its not too complicated to do, switching to a tube round or square is the best option. C-channels are just by design quite flexy like you have seen.

[MrForbes]

if you post some pictures of the robot, and the parts that are twisting, we might be able to help you figure something out. Otherwise we're just guessing..and that doesn't help you much

[IndySam]

Best way to strengthen a channel is to box it in. One way is to bolt on another C as sugested or you could weld a plate to the open end of the C.

[MattC9]

Ill say it again, square tubing 1/16in thick, its light, durable, and some-what cheap. If you don't have a local hardware store that has any you can get some from McMasters for under 10$ and it will ship in 18-24hrs.

Here's the URL for it http://www.mcmaster.com/#tubing/=b829jk

[MrForbes]

I live in a small city, there are at least 4 local stores that sell 1x1x1/16" wall aluminum square tubing. But I don't know if it would fit onto your robot easily. Also, round tubes such as ABS sewer pipe will not twist, and are readily available in several sizes (ID from 1.5" to 4" is very common), and might be more easily adapted.

[Bruceb]

Squirrel, what local stores sell 1x1x1/16 sq al tube? We use a lot of it and always have to special order it from a local metals supplier.
Bruce

[Thermal]

We managed to strengthen a bit of our cbase from twisting the way you mention by fitting in some 1010 8020 (1" x 1" extruded aluminum) into the channels and bolting it down. Maybe you can try that with some square tubing. We also used the 8020 in the cbase for mounting purposes but for just strengthening i'm sure just square tubing will work alright.

[MrForbes]

Originally Posted by Bruceb

Squirrel, what local stores sell 1x1x1/16 sq al tube? We use a lot of it and always have to special order it from a local metals supplier.
Bruce

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.

[Taylor]

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.

I can attest that Lowe's carries it.
So does Menard's.