Payload learning backwards


Hey guys, new to the forum game. But I have a slight issue and was wondering if anyone could provide assistance. Shown in the picture is our gear box atop our reverse double four bar. It may not be so apparent in the picture, but the entire thing is leaning backwards. I’m assuming this is because the tray extends backwards and the weight is causing it to do so. How do I counteract this? I’ve put bearings on each joint with nylocks. It seems to be a combination of the entire arm leaning back from where it pivots at the towers. Any and all help is appreciated.

It would be helpful if you sent us a picture of where the towers are connected to the base


This is the best I have at the moment. I can put another one up in a couple hours if needed.

I haven’t built a DR4B before, but have you made sure that your lower 4 bar has the same length or bars and mounting points? The picture makes it almost look like you’re just a square off. Otherwise I would just make share it connects to the frame securely at a right angle.
Edit: upon further inspection, make sure the lower 4bar is parallel. It looks like you might have varied where the joints in the bearing are (a more side on view of the lower 4bar would be helpful)

Also, your banding seems off. Check that when the arm goes down segments of the triangle get bigger and when the arm goes up segments get smaller.


E: the bottom bar of your first 4 bar is one hole too short? Shorten the top bar of the first 4 bar or move the joint

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this also is a problem with double 4 bars they tent to tip to a degree

I counted the holes and they are mine tall and 23 long

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Huh, maybe the difference between the diameter of a screw and the high strength shafts you’re using is enough to cause that (although I highly doubt the difference is significant). The only other idea I have is that your screws have shifted slightly in their holes due to the force of the lift on them. Hopefully it doesn’t affect your robots performance too much


Hasn’t been terrible. We don’t drive around with it up, just a little issue that’s be nice to address. Screws shifting would make sense.

Just out of curiosity, what’s with the random linear slide on it?

We wanted to support the two bars. They seemed to start bending In towards each other during to lots of rubber bands. We are working on elastics, but any suggestions on elastics would help.

I’m no expert on dr4bs, but if you need enough rubber bands to the point that the lift starts to warp, you might have something wrong

Agreed. I’ve never had that happen

It just seemed like it needed support. Not an obvious bend if one at all.