so i’ve been wanting to make a two speed robot for the past few years, and i’ve learned that using a 6wd, drop center wheel was the best way to do it. it uses AM supershifters and a custom aluminum frame. to try and make use of my teams skill with 8020 i tried to incorporate it into the base to allow for further attachments.
nice. you integrated the super shifter into the chassis very well!
how are you running / tensioning your chain?
That looks very similar to our drivetrain this year with a few exceptions, the most notable being ours was a single speed. Some suggestions I have for you. The outer wheels look like they have bearings in the frame. You dont need the bearings as the kit wheels have bearings in them. You can use a 1/2" round standoff that is bolted in place as an axle and it will serve to strengthen the frame. Also you can have the axles on the end slide horizontally in slots to tension the chain. Another thing would be to not have the 80-20 on the ends run into the standoffs. It will require very long bolts which equal more weight. Finally it is ok to use 80-20 if you really want to but using simple 1" box tubing is much lighter and if welded will likely be stronger as well.
Overall though, it is an excellent design and you should look into building it this summer to work out some of the kinks.
Maybe use the 1 inch box tubing for the bottom structure and only have the 80-20 on the top as a mounting surface.
Oh! very nice job, it looks good.
I actually really like that idea. It would be the best of both worlds. Really the only reason to use 80-20 is because it is easy to build with with not much planning. It is really to heavy and not strong enough for the weight for much else.
I’m all for 80/20 in the right situation. The best use of it on a drive system I’ve seen came from my alma mater of 1293 in 2007. Consider:
The two bolts centered vertically with the 1293 are 1/4"-20 bolts holding each drive pod to the center rails, which appear in this photo to be 1515. Heavy, yes, but it’s a pretty short length. The 1515 goes straight through to the outer plate on both pods, tying it all together (and providing pretty awesome nice mounting options for a mechanism to boot).
They haven’t had any issues with that aspect of the robot to my knowledge, but I also changed teams right before that season. Someone who was active with D5 that year may be able to tell you more.
thanks for the suggestions. just so you know, the connection between the standoffs and the 8020 pieces was not to be a really long bolt, just a 1.25" long coupler bolt. and im not sure how much our team will be able to change in just one year. in prior years, we have used only 8020 for our entire frame, so anything else would be a major improvement. and to tension the chains, i thought to have some sort of lever arm coming off of the center of the “X” in the side panels, which would connect to a roller which would connect to a spring. but this could be overly complicated. or something like this: http://www.chiefdelphi.com/forums/showthread.php?t=63443&highlight=chain+tensioner
We did the slots that the axle slides in and then is locked inplace by tightening bolts on each side. This method works extremely well and does not add any weight. I would definitely recommend it over adding an idler that slides and is locked in place like the picture you posted. We used #25 chain and we never had a single problem with our drivetrain the entire season.
Looks a lot like 25’s drive train but they run it with gears instead of a chain.
okay, so i have been further adding features, trying to figure out how to tension the chains. im not too comfortable with moving the wheels in sliding shafts, so i added a bar of sorts to tension the chain.
the lines represent the chain, and the circles represent sprockets and tensioners. the small circles, the ones that appear to be in the slots, are composed of two tubes, the outer being of HDPE, and the inner of polyethylene. the intent was that a bolt would run through these two tubes, and would be able to slide up and down the slot, in order to tension the chains.
You want to shoot for around 120 degrees of chain wrap as a minimum and I think with your current run, you will see major slippage problems with you center axle.
Try moving your tensioners inward or split it into two separate chain runs.
yeah, i guess i didnt make that clear enough, there would be a separate chain going in each direction
this is the classic thread of one infected with the FIRST bug. i love it!
If that’s one chain run, then I want to know how he got a spiral chain wrap.
It’s two, with about 180 degrees for each chain and sprocket.
Oh, sorry. Looks good then. I know you designed this to fit the supershifter gearbox, but it might be easier to make if you used 4" tall sides instead of 5".
With 5" sides, you would need to order plate and cut it to length and width.
With 4" sides, you can just purchase 4"x3/16" Extruded Flat Bar and cut it to length.
I guess if your gonna CNC or waterjet them anyways, it isn’t that big of a deal, but I’m pretty sure flat bar is cheaper than plate anyways. (I can not find 5"x3/16" extrusion anywhere).
Looks good, nice and simple like it should be. I’d prefer just using dead axles in this particular set up for the end wheels, it would probably cheaper and easier to build. Either way, it looks like a very solid drivetrain.
Does anybody else notice the trend lately of putting the wheels between two plates held together with standoffs? I may be imagining, but there seem to be a lot of teams using this method recently…
I agree there has been a trend for this and we are guilty of it as well. I have tried many different drivetrains and this method (2 plates with standoffs) really seems to be the best one I have done. It is particularly good if you are sponsored by or have access to sheetmetal stuff aka Laser or waterjet because the entire frame for the drivetrain can be knocked out in a couple hours. Also it allows for really quick assembly and wheel changes as well as it is super easy to incorporate the transmission into the frame, thus reducing weight.
We actually originally designed our drive base to use 80/20 or 1x1x1/16 box for versitillity in case we didn’t have welding capabilty anymore. I’m all for that type of flexibility.
I however disagree with your comments on weight and strength. The shape of 80/20 gives it superior stiffness to 1x1 and the weight is comparable to 1x1x1/8 tube if you actually look at weight per foot among other things.
so, i have been trying to design a lighter chassis than this years robot (at ~60 lbs) and i came up with this:
by my calculations, it will move at 14.82 ft/sec high gear and 5.79 ft/sec low gear. i have also figured the weight to at at around 45 lbs.
and just for future reference, 1x2 8020 weighs about .98 lbs/ft, and 1x2x.125 aluminum weighs about .88 lbs/ft. not much of a difference when the strength is taken into account.
Great job here. The concept looks very similar to the 25 drive adaptation that 103 has been running with good success for a couple years. They swear by the 8020 ease of prototyping and retrofitting. You may want to get in touch with them to bounce ideas around.