Need Help with our build

We have a problem with our passive lift D4RB we cant get the lift to grab and pick up so its not lifting when we need it to any ideas

How many motors are you using? What gear ratio?

Send a pic of your passive, there are tons of potential problems.





I don’t see anything attached to the end of your dr4b, where’s the passive?

We have the passive finished, but we are more concerned about the arm that isn’t working.

Can you lift it by hand? Is it difficult to do so?

Yes but it is a bit difficult.

Then I’d say your problem is likely in build quality. One thing that stands out is that you have motors trying to drive the lift at different speeds (the ones on the base tower driving at 1:5, and the ones on the elbow driving at 1:1). I didn’t stop to count, but it appears that the bottom four bar is not actually a parallelogram. The driven 60-tooth gears on the base towers are also not supported on both sides, so they’re going to try to creep away from the driving gear and skip (you can see some of that in the picture, that the axles aren’t parallel). Add that the base towers don’t appear to be standing straight, and I’d summarize the problems as:

  • Too much twisting and parts out of square causing axles to bind
  • Not enough torque due to low gear ratios (two motors at 1:7 would have more torque than the 4 you have in this configuration)
  • No rubber band assistance to bear the weight of the arm

thank you sir this is very helpful.

Ideally, the gears should be screwed to the lift. Also use high strength gears when doing anything that requires more than a few pounds of force as you’ll end up stripping out the insides of those gears.

Edit: I can send you pics of my lift through PM if you want

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They’re attached to the axle with lock bars.

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You also shouldn’t cantilever the gears like this.
A dr4b like this one would probably be a lot more efficient, and you can use 2 100rpm motors on a design like this.


Here’s an example of a dr4b, simple design, instead of using axle joints, use screw joints with bearing flats, as it reduces slop, and you might want to make the motor not cantilevered, as that could cause some long term problems with gears stripping, metal bending, or even the motor mount breaking.


these motors are doing nothing, you have them attached directly to the dr4b arms, trying to lift a dr4b with no gear ratio is not going to happen, try a 1:7 or 1:5 gear ratio.