Problem with the arm bouncing

The problem in my bot is that the arm is bouncing and i don’t know how to stop it from doing that. I am using rubber bands as a counterforce to all the weight the lift system has. Right now i think i should use the rubber tubing Vex supplies because it doesn’t have that much rebound as rubber bands.

Use a potentiometer to measure the position of the arm, and write some code to maintain the arm at the same position.

As far as mechanical fixes, there are a few things you could do.
I prefer not to use stretching materials at all, just gears and/or chains/sprockets. If the arm’s heavy, just configure the gears for more torque.
Another thing I found to affect bouncing is the weight distribution throughout the arm. Try to equal things out with counterweights and such.
Another thing, that goes along with the torque option, is the speed at which you’re lifting the arm. sometimes this will have an affect on bars rotating longer than you tell them to.
The last thing I can think of is the play in your gear set up. make sure the plastic that the square bars go through is not worn away. i recommend high strength gears with the metal inserts if the problem is continuous

Hope I helped,

Code with a quad-sensor on the arm is the way to go.

Set your motor speed to be a proportion of the error between where you want the arm to be and where the arm is. This will give you an offset from your desired position but you can simply change the target point to suit.

Speed = K * error

This is the P part of a PID control system.

Make sure the constant K is not to big or you will get resonance/overshoot (bouncing) that is too big.

In RobotC you can even have a task looking after arm position all the time and just change a global variable to move the arm.

Hope this helps.

Definatly try the rubber tunbing from Vex. It is probably the easiest thing to try.

When you say bounce what exactly do you mean? Does the arm wobble up and down when you go over a bump? If so then you want to stiffen the arm a little. If you could slow down time I expect you would find the arm is bending in the middle somewhere. Try bolting a piece of c-channel along your arm.

If you arm is that heavy, I would think that you are actually bending the axle that the the arm is attached to. The latex or rubberbands really have nothing to do with it. Adding another set of braces to connect the gearbox and the arm off the axle say 2 inches outside of the origional ones will definately help.

I have noticed that the vex gears have a considerable amount of gear lash (there is some space in between the teeth of the meshing gears), so try using more gears, like the Syntax Error’s robots (no offense, but their gearboxes are huge!) I also noticed that with the metal bar locks, if you are using those, be careful how you put them on. The part that latches onto the shaft isn’t very tight, so it can wobble quite a bit. Can you please post a picture of you robot? That would help.

I hope this helps!

Right Now i am using a long axle to connect to the gears.Basically we have the Metal Pinion gear running the high strength 60 tooth gear. This is the only pic i have right now because my bot is at school.

Once again, taken as a compliment.

On the top of our “huge” gearboxes we usually attach the arm in two places, our little trick is to use 60 tooth gears instead of the metal lock bars, you can kinda see it at the top of this pic.

Clever! I hate those metal lock bars, they barely work for their purpose!

From the picture posted it looks like you could be getting flex in your axel. More gears side by side would help with any gear lash and i see you have gears with holes in them. Make some plates on your arm that you can attach bolts that run through the holes in the gears. This will help dramticly.

Yes, i second this action.

Do i directly connect the arm to the gears?

yes indeed

When the bot is moving the arm bounces up and down thus causing the arm to lower down. What i have see is that the gears a space to move which causes the arm to move up and down. Right now the top gears are connected to each other by an axle. This may cause the bending your talking about.

Right now i have a 5:1 ratio should i increase?

If the arm is backdriving using a higher ratio will help. An easier solotion that you might want to try first is adding more latex tubing/ rubber bands. Not sure if that will work though.

Are the gears actually going away from each other, so they don’t always mesh while moving? If so, you’ll have to strengthen the axles themselves, or support the gears more with more bearing blocks closer to the gears. You also have to make sure that you did not position the gears diagonally from each other, because i have noticed that there is extra space which makes it easier for the gears to bend and stop meshing.

It may also be possible to support your gears by putting another gear on the opposite side of the gears that are moving away from each other to support it and hold it in place. This support gear doesn’t have to drive anything, it’s simply there to add stability.