dr4b tilting.

We have just started having a tilting problem with our dr4b. Whenever we try and raise our lift with 2 cubes one side is extremely slower than the other causing it to tilt to the side. This only occurs with 2 cubes, and at first only happened when our battery is low but now it has started happening all the time and it also started titlting a lot when ever we would lower our lift (this never happened before). I decided to switch all the motors to brand new ones and the problem still occurred. I also changed out all the wires and motor controllers as well as check to make sure all the set screws are the same tightness. I even took off all the rubber bands and put new ones on evenly on both sides. The problem still occurred but almost worse. I’m planning on putting the lift on a power expander and even switching out the cortex but with the limited time we have I would rather not do that. Any ideas as to why this is happening?

Btw we have a plunger intake and 2 motors on the lift towers and 2 motors on the second pivot tower.

I would add more cross supports and have code adjust the lift based off of the tilt. There has been quite a few threads about how to do this with IMEs easily. Mainly its set up a P loop where the goal is average of the 2 lift sides.

We can’t use IMEs because of sizing what other option do we have? Would potentiometers work?

A few simple mechanical things that might be the issue:

  • Make sure the rubber bands on each side are equal
  • Make sure the pivot points are the same (correct) tightness
  • Make sure there is not binding or extra friction in the gearing or pivot points
  • Slightly pull the axles from the motors and move the lift by hand to try to find specific bad spots
  • Make sure you’re using all the same gearing in your motors
  • Make sure everything is symmetrically balanced.
  • Make sure your entire lift is square (the arms are 100% parallel)

We had the same issue and cross supports definitely helped a lot. Something else that you can do is to add more rubber bands on the side that is lifting lower (or not as high). This is more of a temporary solution but it worked quite well on our robot, though you will have to do some guess and check as to how many rubber bands to add.

We have done all of this and still have the same problem but what is a quick way to check if the arms are 100% parallel

This would most likely solve the problem with it tilting on the way up but just make the tilting on the way down a 100% worse. When it goes up the right side is slower so it tilts to the right (twists) but when lowering the lift tilts (twists) to the left.

You can use Shaft Encoders instead of IME’s.

A picture of you lift would make your issues a lot easier to spot.

Start with the vertical bars that are mounted to the drive. Measure the width (left side to right side). Then measure the width of the same bars at the vertical gear tower. They should be the same distance away at any point. Do the same for the top bars.

I say this because I have seen a member of my team force a support on that was not long enough. This caused the lift arms to squeeze together and made everything more inefficient.

This is the only one I have right now. I can probably post a better one later

Doesn’t look like there is much crossbracing, all I can see is 2 c-channels and 4 bars. Our rd4b had 5 c-channels and an angle and it would still slightly tilt (actually leading to us tipping during state finals :frowning: ).

We have actually added a couple more than that because that picture is old (hence the conveyor) but it would actually lift up perfectly straight with that amount of cross bars but we did add 3 more hoping it would help

And not that it matters but there are actually 6 bars :wink:


Not enough bracing and wrong type of bracing, take the X-bracing off. That type of bracing is good for parallel linear bracing. You need to add side to side bracing. I edited your pic below to help illustrate what you need.

Follow his advice, that’s a very good bracing set up. And honestly, if you have the room for more bracing, add it. As long as it isn’t hurting your compression it will only help your lifting. And make sure some of it is steel(maybe one of the top and one of the bottom 5 wide c channels). Steel may be heavier but it can be worth it because it doesn’t flex as much as aluminum

Thank you we will definetly try that just I’m not sure we can add the top wide c channels because they do not fit parellel do to spacing (the holes don’t line up) is there any other way?

From what I have seen, X bracing can actually work very well in this situation.

Try putting X’s on both the top and bottom bars on each of the top and bottom sections (4 total).

Use the 2 wide c channels instead and line up one side with the double holes and the other the single. Use as many as you can fit. It wont be square but it works. Make sure to use nylocks because that one screw will tend to come out.

Okay I will try that and see if that helped. I will post more photos of it later today.