DR4B is tilting to one side

Hi,
This is our first year in Vex Robotics. Our team has decided to use a double reverse four bar as our lift. However, we are having some problems with it. The lift leans to one side as it goes up, but corrects itself at the highest point. However, this makes stopping halfway up really difficult. We have connected both sides with many crossbars, but they do not seem to help. We already have 5 rubber bands on each side. Is there anything we can do in order to stabilize it? I was considering a PID loop to correct the error, but I figured there must be a mechanical way to fix this.

I will upload some photos when I get a chance.

Just a few thoughts:
Are you sure that the motors driving both sides are all geared the same?

Are you sure that your code is commanding the motors to run at the same values?

If you have two batteries and a power expander and are running different sides of the lift off of different batteries, are you sure the batteries are both charged?

Have you checked to make sure you don’t have excessive friction somewhere, or some metal parts rubbing or wires tangling just as the lift goes up?

Is the lift generally struggling when it rises? If so, have you considered adding rubber bands to assist the lift?

Are you sure that all of the motors are actually powered and turning?

Yes, we haven’t ever opened up the motors, so they are all geared up for torque.

Yes.

We don’t use a power expander for our lift. Would that help?

Yes

The lift seems to be fine as it rises, except for the tilting. But we do use rubber bands on both sides.

We tested the motors not too long ago, and they all worked then. I’ll test them again soon and update.

Thank you for your prompt response

I have this problem, but it’s not when it gets power, it’s just in general and i’m trying to find where its skewed but I just can’t.

A power expander would not necessarily help with the tilting. I just mentioned it in case you had split the power usage for the two sides, in which case a dying battery powering one side might sag compared to a full battery powering the other. Some kids use power expanders so they can use two batteries but don’t think about how to distribute the power in a balanced way. I was just trying to rule that out.

Maybe some photos would help. Often, this kind of tilting is a faulty motor problem, bad code, unmatched gearing or a friction/bad bearing problem. Also a strong mechanical connection is needed such as C-channels running from one side to the other. Those cross supports need to be screwed down very well so they can transfer force without pivoting, wiggling around, etc.

If you are using rubber bands on your lift, then there might be too many on one side or too less on the other. It could be that or that your gears used on your lift are warping.

Are you sure that the gears on both sides are aligned the same?

Please check for any points of friction on your lift that may be bad. For example, metal tends to have a lot of friction with other pieces of metal, so avoid metal-metal contact in as many places as possible.

Have you tried replacing the rubber bands? Our team switches all of them every 3-4 matches because they stretch out; maybe due to some minor tilting previously the bands on one side are more stretched than the other, which tilts the lift, which stretches the rubber bands, which… You get the idea.