pic: 2009 robot idea

[s_forbes]

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...

[sdcantrell56]

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.

[Peter Matteson]

Originally Posted by sdcantrell56

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.

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.

[pacoliketaco]

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.

[Waynep]

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.
-wayne

[Alex Cormier]

Originally Posted by pacoliketaco

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.

Looks great, good job on the improvement. I do make one suggestion, I have experienced similar type of tension systems. I say instead of a stright shot for the tension to be calibrated, I would recommend them to be holes every 1/8" or so. This will greatly improve on the idler not slipping from having too much force applied to it, and you are always sure that it did not move during a match.

[pacoliketaco]

Originally Posted by Alex Cormier

Looks great, good job on the improvement. I do make one suggestion, I have experienced similar type of tension systems. I say instead of a stright shot for the tension to be calibrated, I would recommend them to be holes every 1/8" or so. This will greatly improve on the idler not slipping from having too much force applied to it, and you are always sure that it did not move during a match.

i guess in the rails in which the tensioners ride, i could just put a few holes/dimples that allow the screws to tighten further than usual.

[Dan Petrovic]

Originally Posted by pacoliketaco

so, i have been trying to design a lighter chassis than this years robot (at ~60 lbs) and i came up with this:

That's actually not a bad weight for a chassis (in my opinion, of course). What I like about heavy chassis' is how your center of gravity turns out when you're all finished.

With a chassis that is less than 60 pounds, a majority of the weight is going above the chassis, raising the center of gravity to a less desirable place. Our center of gravity in 2007 was seriously at the bottom of our chassis. Teams would really have to try to get us to tip over. That chassis was probably close to 80 pounds.

[Tom Line]

One thing - I always like keep things simple and easy with few parts.

Have you considered just using aluminum C-channel (or even square tubing) for the left and right areas where the wheels are? A hole saw can make quick weight savings holes, and you don't need the fasteners, the machining, etc. It's stronger, lighter, and easier to make. Just a suggestion.

[sgreco]

Originally Posted by InfernoX14

That's actually not a bad weight for a chassis (in my opinion, of course). What I like about heavy chassis' is how your center of gravity turns out when you're all finished.

With a chassis that is less than 60 pounds, a majority of the weight is going above the chassis, raising the center of gravity to a less desirable place. Our center of gravity in 2007 was seriously at the bottom of our chassis. Teams would really have to try to get us to tip over. That chassis was probably close to 80 pounds.

This conversation about weight is interesting. My team's did a swereve steer this year, it weighed a little over 90 pounds. Once we added the electronics and compresor it weighed 100 pounds. Then with the battery it was closer to 110 pounds. All of this was about a half inch from the ground(maybe an inch).

[=Martin=Taylor=]

Originally Posted by pacoliketaco

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! The level of detail in the CAD is amazing. How'd you make the chains?

This is VERY similar to my team's last two drive trains. This kind of system is very adjustable and easy to build. It's worked great for us these last two years.

2007:


2008:


Some things to consider:
5.79 fps is probably a little two slow. We ran low gear at about his speed this year and it was useless. The slowest I would go is 7 fps.

You could save more weight with #25 chain. This system makes chain tensioning a breeze, and you could easily implement #25. We used #25 this year and never lost a chain.

I'm curious as to why you put the axles on the center line of the extrusion. It would be a lot easier to put the pillow blocks on the top or bottom. You could save a lot of machining, and replace the 1020 with 1010.

Altogether great work though. Are you gonna build a prototype?

[whytheheckme]

A note on the weight.... Remember that this year's control system will weigh significantly (3-8 lbs., if I recall correctly (someone correct me)) more than in previous years. It also will require quite a bit more (continuous) space than in previous years.

Love the design. We need an overhaul on our concept of the idea of a 'working drivetrain' (currently my team is having trouble with that concept), and this is a great place for us to start!

Jacob

[team2061]

Originally Posted by Hachiban VIII

Great Job! The level of detail in the CAD is amazing. How'd you make the chains?

This is VERY similar to my team's last two drive trains. This kind of system is very adjustable and easy to build. It's worked great for us these last two years.

2007:


2008:


Some things to consider:
5.79 fps is probably a little two slow. We ran low gear at about his speed this year and it was useless. The slowest I would go is 7 fps.

You could save more weight with #25 chain. This system makes chain tensioning a breeze, and you could easily implement #25. We used #25 this year and never lost a chain.

I'm curious as to why you put the axles on the center line of the extrusion. It would be a lot easier to put the pillow blocks on the top or bottom. You could save a lot of machining, and replace the 1020 with 1010.

Altogether great work though. Are you gonna build a prototype?

i saw that u guys used pneumatic wheels on the 2007 robot...we were going to use that this year but we couldnt find a way to mount sprockets on. Were those sprockets custom or were they bought?

[pacoliketaco]

thanks for all comments/suggestions. i guess i could change the sprocket on the two wheels powered directly from the transmission to something smaller. the main reason that i wanted to use 1020 and mount the axles in the center was for strength. the past three years, we had a very similar drivetrain, which i felt was excessive, but then again, it was very robust. the reason i want a light drivetrain, is that in the past three years my team had been in FRC, we havent had a complicated robot. our other systems end up to be too heavy, and we have to make accommodations by making simpler mechanisms. this year i dont want to have to worry about weight, and starting off 10+ lbs lighter will help.
2008:

2007:


i wanted to make something that was only one level of 8020, to reduce weight. in the past i noticed that a single 1010 rectangle bends too much, so i decided to use 1020. using only 6in wheels, by putting them on either the top or bottom, there was 7/16" of clearance (too little) or 3.5" (too much)

about the weight of chain, #35 chain weighs only .21875 lbs/ft, and with 9.5 feet of chain that is only 2.078 lbs. switching to #25 chain, which weighs .085 lbs/ft, would save 1.27 pounds, which isnt much for all of the added trouble. the purpose of all of my designing is prep for next year, as our team doesnt have the time/materials to build a chassis during the summer. just to see that your team seems to have built the same thing that i wanted to make, shows that i am headed in a good direction.

as to how i make the chains in autodesk, i just use the KOP download, and modify each link a little bit. i added a VERY small rectangle in the center of them, in order for an angle constraint to hold them together. or you can ground one end of a set of links, and simply drag the other end away from it, until it is straight. once you do this, you have length of straight pieces of chain, but you still need the curves. to do this, i find the distance from the center of each sprocket to each other, and make a new assembly to work out of. i then add in the links one by one, making them fit around the sprocket. then i add in the straight pieces, and put the whole assembly on the finished robot. its a lot of work, but it looks awesome =]