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.
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. :ahh:
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.
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).
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?
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
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?
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:
http://i37.photobucket.com/albums/e82/pacoliketaco/robotdrivetrain.jpg
2007:
http://i37.photobucket.com/albums/e82/pacoliketaco/robotchassis.jpg
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 =]