Vex V5 DR4B Banding Help

VEX V5 General Discussion
1

VEX V5 DR4B Lift Gets Stuck in the Middle — Rubber Band Tension Issue

Hey everyone! Our team is having trouble with our Double Reverse 4-Bar (DR4B) lift, and we could use some advice.

The problem:

Our DR4B gets stuck around the middle of its travel. We are using rubber bands to assist the lift, but it seems like the rubber-band tension is unbalanced with the motors.

  • When we try to lower the lift, the rubber bands seem too strong, and the lift won’t come down.

  • When we try to raise the lift, the motors seem too weak to get it through the middle.

  • The lift basically gets stuck in the middle and won’t reliably go up or down.

What we need help with:

  1. How should we adjust the number, strength, or placement of rubber bands on a DR4B?

  2. Where should the rubber bands attach to provide useful assistance throughout the lift’s travel?

  3. How can we balance the rubber-band assistance so the motors can raise the lift while still being able to lower it?

  4. Could the DR4B’s geometry or leverage be causing this problem specifically around the middle?

  5. Should we change the motor gearing or check anything else before rebuilding the lift?

We want the lift to move smoothly from fully lowered to fully raised without getting stuck.

If anyone has experience tuning rubber-band tension on a VEX V5 DR4B, we’d really appreciate your advice!

Thanks!

2

We are running a DR4B this year as well, and we had a similar problem. We had to make sure of a couple of things. A). We made sure that as the lift expands, the rubber band triangle contracts. B). We added more rubber bands to the lift. However, this can apply differently if you are having downward problems. In your case, I would recommend adjusting your triangle to use as little banding as possible, but having just enough that your lift can float when the bot is turned off. Your issue is likely too many bands in combinaton with triangle tuning. Find what best suits your bot. Your geometry is likely fine.