Descending robot arm

[Chris Hibner]

Originally Posted by Robby Unruh

So this year our arm is a little different from the majority of teams. Ours is an actual "arm", with two joints. I've only seen one or two like it on CD, and I'm proud to be somewhat unique.

My question is that when we move our robot arm down, it falls quickly, and the only way to safely descend is to sparatically press the down button every half a second or so. I've done everything I could in the programming to try to slow it down, but no luck.

We are using denso window motors with chain drive, and Java programming. Any help would be greatly appreciated.
Thanks.

Do you have any feedback on the arm (encoder or potentiometer)?

Can the arm travel beyond vertical (i.e. can it reach to the front-side and back-side of the robot), or is it confined to one side of the robot?

Any pictures you can share?

[Brandon_L]

We had a similar problem. Its all about the counterweight. We were using bungee cords, and when there were no forces holding the arm down, so it was free spinning, it would only sit about an inch from the floor. We then found a heavy duty spring, it started out at about 4" long. We swapped out the bungee cord for the spring and now when its free spinning it wants to stay almost perfectly horizontal out, stretching the spring to about 7". It made all the difference in the world.

Before: http://www.youtube.com/watch?v=a_yD4oc4j2g (doesn't actually show it coming down, as we were afraid to break...everything)

After: http://www.youtube.com/watch?v=KB1veyKNYQI

I don't know how this will help you with a double jointed arm, I don't know how exactly yours works.

We also had problems with the window motors locking up, switching to victors and putting them in break mode fixed that.

[Robby Unruh]

Originally Posted by Brandon_L

We had a similar problem. Its all about the counterweight. We were using bungee cords, and when there were no forces holding the arm down, so it was free spinning, it would only sit about an inch from the floor. We then found a heavy duty spring, it started out at about 4" long. We swapped out the bungee cord for the spring and now when its free spinning it wants to stay almost perfectly horizontal out, stretching the spring to about 7". It made all the difference in the world.

Before: http://www.youtube.com/watch?v=a_yD4oc4j2g (doesn't actually show it coming down, as we were afraid to break...everything)

After: http://www.youtube.com/watch?v=KB1veyKNYQI

I don't know how this will help you with a double jointed arm, I don't know how exactly yours works.

We also had problems with the window motors locking up, switching to victors and putting them in break mode fixed that.

Our arm is incredibly similar to that, our second joint is pneumatic so it's only got two ranges of movement. So how do you think we'll do using surgicial tubing as our counter weight? I don't think we have time to get/order springs to use before shipment.

- edit -
is enabling Break Mode on the victors safe? I've never heard/seen anything about that.

[Brandon_L]

Originally Posted by Robby Unruh

Our arm is incredibly similar to that, our second joint is pneumatic so it's only got two ranges of movement. So how do you think we'll do using surgicial tubing as our counter weight? I don't think we have time to get/order springs to use before shipment.

- edit -
is enabling Break Mode on the victors safe? I've never heard/seen anything about that.

We put the victors on, and before we had it in break mode the arm liked to just keep going down for no reason at all (made no sense to me, as they can't backdrive, right?). Whatever the problem was, break mode fixed it.

I posted a topic on here and asked about it when we had our problem, and everyone suggested surgical tubing, so I think you'll be fine with it.

[Robby Unruh]

Originally Posted by Brandon_L

We put the victors on, and before we had it in break mode the arm liked to just keep going down for no reason at all (made no sense to me, as they can't backdrive, right?). Whatever the problem was, break mode fixed it.

I posted a topic on here and asked about it when we had our problem, and everyone suggested surgical tubing, so I think you'll be fine with it.

Great, it's just too bad we can't test it out now since we disassembled our robot arm last night for shipping. Thanks for the tip though, it's a shame we'll have try it out during the practice matches.