Hello everyone,
I would just like to ask if anyone knows of any problems that could come about by having a double reverse chain bar (similar to a double reverse 4 bar)
Thanks!
I’ve never done a chain bar version, but i’ve done a double reverse 4 bar(and a kind of bad experience with it)
I think it might be possible and reliable if you have aluminum. Whether it’s worth in compared to an 8 bar? i doubt it. The first issue you’ll need to tackle is strengthening your chain or reducing the weight of your system. The first thing that’s going to give is the chain. The bottom stage of the chain will handle about 8 pounds of weight, 12.5 inches away before it’ll give. if you decide to tackle chain snap with simply more chain, your next issue is going to be axle length. To solve axle length, you can counter with supporting the axles from above or below, however that reduces your max height by a few inches. If you decide your going to do some heavy lifting, then your axles will be even longer to accommodate for the additional gears. Once you apply those additional gears, you still have to ensure both stages are powered together. You typically need to cut metal if you decide this. Another issue you’ll probably face is raising at unequal intervals. The only way i know around that is fine tuning motor values, properly adding rubberbands, and redistributing weight. The next issue is sideways bending I believe if you place linear slides to support the sides, rather than cross bars like other linkages, you might get a reinforced system. The reason why sideways bending cannot be ignored is cause your axles will face stress. If your axles face stress, your gears will unmesh slightly and your gears are the heart of this system. Another issue is if you decide to ignore powering the system together and simply have a higher torque ratio, you must limit your weight. If you stress the axle past the theoretical 118 inch pounds of torque, it will twist. Also, if you happen to be under 118 inch pounds, you will need double up your gears on the last stage(making your axles even longer). Without that, teeth will begin to come off. Other things you can do is add elastic(which somewhat helps) and program to reduce jerk. Another annoying thing is electronics, but that’s doable with time.
All of these issues will be mitigated if you have aluminum!! if you can pull this off, then you’ll have a system that can reach pretty high with a really good COB.
People build arms out of steel? Why? Is there something we’re missing? We always assumed they were bad because of the weight.
My team used a reverse double 4-bar this year. We encountered large amounts of slop, so with a chain bar, you may encounter even larger amounts of slop I guess.
It is bad. My team has a bunch of metal, unfortunately its mostly steel. Since we’re spread out thinly, we have a really low budget. We just make the most of what we have
Okay thank you for your help… I will be sure to make my robot as light as possible (is <10 lbs possible?) 
Depends on what you want to build. Our robot this year was… 24-26 lbs? But that was two full steel bases, 10 wheels, 10 motors, half a scissor lift, two batteries and all the other stuff that adds weight.
Your planning on making this a hanging mechanism?!:eek:
Though i’m in for crazy ideas… i don’t think that’s happening without serious engineering. A gateway robot was typically 11-13 pounds. The first issue u need to tackle is torsion. If your axles experience more than 118 inch pounds then they’ll twist(from what i’ve read). My suggestion is that you look into planetary gearing like i have. With that, you can have a higher torsion limit
Can’t I just bring 20 axles to a competition and switch them if they break? I was just going to assume with as cheap as they are I could build a design that chews through them and switch as I need to. As in, making the axles that were likely to bend easy to remove as part of the design.
This year one of our designs needed new 18" axles every competition. We could do around 45-50 lifts on them, but after that they were too bent to continue working correctly. It probably indicates we made something incorrectly, but the design was otherwise structurally sound. Tank-like, even. Once we get back to school Monday I THINK the plan is to share both of the defensive designs we made in detail here. Some people here saw one at Worlds, but there was a different one that was nearly as effective.
At the cost of weight it could be possible to use the turn table bearings. They can handle a larger load but are an extra piece to buy and are harder to implement than a single axle.
What if I was using circular inserts for the gears… That should lessen the torsion. right?