We are attempting to use a double reverse four bar, but it is extremely heavy and barely lifts even with 2 motors and a TON of rubber bands. The screws attaching the gears to the channels are bending (even with standoffs there) and making the bars not parallel as well. Any suggestions?
Hello!
First things first I think its important to understand a DR4B and how it works. You don’t need gears on each arm. That would shorten and lighten up the box on the DR4B. It seems that the bracing is alright on what you currently have although I can not see it all. I also can’t tell if your joints are on nylocks or keps nuts (I could just be missing something I am at work lol). There are a lot of decently built DR4B that I think you can learn from.
If you want some inspiration, here is our DR4B from ITZ. Feel free to ask some questions if you have any, I’d be happy to help 
Try screwing the bars directly into the gears themselves instead of standoffs. Also, the first and third gear(starting from the bottom) can be removed.
Although I’m of limited help. I had the exact same issue with my dr4b so I abandoned it.
Oh, I didn’t even realize they weren’t necessary! The joints are nylock, that’s what they are supposed to be, right?
It seems as though the top arms aren’t parallel (the one in the back is higher than the one in front). Also, although I’m not completely an expert on rubber banding (I trial and error my banding), check to make sure there’s no resistance when going up.
Yes, and you don’t want them tightened all the way or else the lift won’t move. A good way to test this is to take of the motor and try to lift the lift with your hand and see how smoothly it moves. (The way that I tightened the nylocks on our bot was tighten until they were tight and then loosened them slightly so the lift could well lift 
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The first and third? I am assuming that you mean the first green plastic gear?(there is a small metal one below attaching to the motor). Isn’t the first one needed to attach to the first parallel channel?
To add on to what others have said, the rubber bands on the top stage are not correctly placed. They should be like the bottom but mirrored. To see if you have the correct amount, take off the motors and the lift should keep in mostly the same place. Also, are the bands at the end of the first stage connected to the gear or the C-channel?
We originally had the rubber bands the way you are suggesting, but that pulled it down. We still should definetly check the placement of them. I do like idea of taking of the motor though. And the rubber bands are connected to the c channel.
Yes, I meant the green plastic gears. Dont remove your metal gears! 
Are you using steel or aluminum?
You need to either reenforce the connection points on the gears or connect them directly to the c-channel. Here are some images of what a good gear box looks like.
(Note These are not my images, they were gathered from another thread ***)
The very bottom c-channel, on the right most image, does not need a gear. In general, the very bottom and top c-channels in a DR4B linkage do not need gears, they just need to be connected directly to the powered arms.
yes one problem I’m noticing is that you have keps nut screw joints, nylocks will certainly hold better, I can’t tell if you already have it or not but try doubling up your bearing blocks (put one bearing block on either side of the C channel) just for that extra support.
We are using all aluminum
You’re gonna probably want to get rid of the unnecessary weight then. Perhaps try taking off some of the gears on the outsides of the DR4B. It would also help to know if you have anything on the end of the DR4B. Also add more rubberbands until it goes up on its own, then remove a couple so it stays down.
This is bad practice because the bearing’s tabs will no longer be in contact with the hole in the c channel and therefore won’t be aligned. In addition, with three things trying to constrain the shaft along an axis, and none of them being perfectly aligned, there is bound to be extra friction.
I am about to take off a couple of those unnecessary gears. The lift actually works very nicely by itself, but we have an extremely heavy attachment causing most of the weight.
I’ve got another question. How would we be able to directly attach the gears the c channels? There is a screw in the way that is holding the bearing block.
If I understand what you’re saying, you would just need to space out the c-channel w/ the gear from the bearing block.