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Re: pic: FRC488 - 80/20 Drive Train
I almost slapped an "FRC100" tag on it... :D But I'll resist...
Kinda reminds me of some of our drive ideas. Our team doesn't actually ues 80/20 connectors, we use bolts with filled off heads, or toilet bolts. This spares us the aggravation of dealing with sliding, twisting, falling-out 80/20 biscuits. Quote:
But how will you reache the bolt if the axle is in it? And how will you tension your chains if the wheel isn't in there? :confused: We usually buy a kind of extrusion that 80/20 sells that already has the flat groove, and then we put the holes in it ourselves. |
Re: pic: FRC488 - 80/20 Drive Train
Instead of the pivot blocks, you might look at the 10 s 2497 parts. They may handle the shock loads better and the 2 " and 2 T nuts grip better. The raw stock can also be purchased if you want to cut your own. Watch the 8020 garage on e-bay. Any reason for the 1/2" shaft? For a dead axle a 3/8" grade 8 bolt is enough and lighter.
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Re: pic: FRC488 - 80/20 Drive Train
Team 980 has used the 1010 size 80/20 extrusion in our robot chassis for years now. Our six-wheel drive with Andy Mark SuperShifters goes together very quickly and getting proper tension on the chains is easy. We use simply-machined phenolic bar stock as pillow blocks for the axles with fastener through-holes spaced at 2". Instead of the more expensive drop-in T-nuts, we use economy triple T-nuts. We haven't had problems with slippage of the fasteners, we put a bit of Lock-tite on the threads and torque them down.
I don't see us changing this approach for sometime to come. Oh yeah, you can save some $$ if you buy from 8020 Inc Garage Sale on E-bay. |
Re: pic: FRC488 - 80/20 Drive Train
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We use the t-slots until we have chain cut and drill through and bolt once everything is in a final position. The bearing blocks we have are slotted and allow for minor adjustments if necessary. Our t-slots always wound up sliding in the 80:20 and wound up being more maintenance that it was worth without bolting through. After 4 years of this, my advice would be to go ahead with the t-slots and if they never slip, great - but leave yourself space to drill and bolt through just in case. It's a quick enough move with a hand drill and some 1/4-20 bolts. |
Re: pic: FRC488 - 80/20 Drive Train
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Re: pic: FRC488 - 80/20 Drive Train
I'm not entirely convinced that this is either stronger or lighter than basing a drivetrain on the KOP frame from IFI, but I do appreciate its simplicity.
Mind you, I'm not counting on having that in the kit this year, and have come to expect something innovative each year from the Xbots in the way of an off-season drive system prototype/model. I also base my KoP drivetrain comments on our experiences with it, and our team has in-house access to mills and a TIG welder that allows us to do a fair bit of "hot-rodding" to it. I do like how this simplifies the chain/belt tensioning. I would suggest adding a second block, inboard of the two outboard axle mounts that has a bolt hole drilled and tapped parallel to the frame rail and is mounted to the frame rail in a similar way to the axle mounts. This way a bolt run through the tapped hole could be used to press on the axle mount and tension the chain very carefully, then the axle mounts could be tightened. Once the appropriate location for the second block was determined, then it could be welded in place, and the tensioning bolt could be secured with a lock nut. This way even if the axle mounts' bolts were to come a little bit loose the chain would not come loose. See you in Portland and (yes!) Seattle! Jason |
Re: pic: FRC488 - 80/20 Drive Train
Our team has used the KOP frame and 1010 extrusions in the past. The Kop frame and a 1010 frame are heavier than needed when the bumpers are added in. The KOP frame is time consuming to assemble. Pop rivets help. The 1010 frame most likely will not be ridged. It will be much heavier than needed. Last year our team used the 8020 quick frame material with the press in connectors. We used the flanged stock were possible . the the flange recesses provide a mounting for clear poly panels. The way we attach the bumpers prevents the tube from separating from the connectors. I was worried about the plastic connectors but, they held up fine. To mount the axles we use 2 2.5" pieces of 8611 panel mount extrusion to make clamp on mounts for 3/8" grade 8 bolt dead axles. With the 1/16" tubing allot of weight was saved and it went together very fast. Our team intends to use quick frame again unless some thing better is in the kit. Nothing like whacking a frame together.
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Re: pic: FRC488 - 80/20 Drive Train
Madison as always great cad work. I like the simplicity of the design and wish my team would try Dewalt transmissions but anyway. I do have one question I noticed you always use omni wheels up front why ? I don't have an issue with it as it seems to work fine for you but I'm just wondering. Looks great can't wait to see it in real life if 488 and 1251 both make it back to Championship in 09. Good luck and nice slick designing.
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Re: pic: FRC488 - 80/20 Drive Train
looking good, just a few questions.
Is the switch to 6" wheels so they can be entirely COTS? Have you considered running 2 CIMs per side? If so, would you just mirror one of those CIM mounts to the other side? Where do you foresee attaching mechanisms/superstructure? |
Re: pic: FRC488 - 80/20 Drive Train
Great CAD work it looks really similar to our gen 8 reference CAD design that we release every year. Take a look:
http://uncert.mines.edu/research/csr/FIRST/Gen8.htm If I may, I would look at some stamped pillow blocks like the AMI Bearings BPP1-8 rather than try to modify some of the 8020 parts for your bearing blocks. Here is a link to there catalog page 15 http://amibearings.com/pdfs/mounted_normal.pdf |
Re: pic: FRC488 - 80/20 Drive Train
I think that, when we start to get to the point where we're adding band-aids -- little blocks here and brackets there -- it's best to start again and reexamine the requirements of the drive.
This design's efficacy, for our needs, is wholly contingent upon using the 80/20 slots for tensioning. If it turns out that it's not effective in that capacity, we'll go back to other designs that, while requiring a bit more time and effort, have worked for us in the past. I wonder if sometimes, people become so attached to an idea that they'll go to the end's of the Earth to avoid acknowledging that it's not the best idea for their circumstances. I think that happens to me sometimes and I'm trying to get better at recognizing that and knowing when to start over. |
Re: pic: FRC488 - 80/20 Drive Train
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If we chose to add a second CIM motor to the drive, I'd have to reevaluate the use of the Dewalt transmissions. I haven't yet compared the resources needed for two Dewalt transmissions per side against those required for, say, a single AM setup. Mechanisms will also bolt to the 80/20. For the past two years, we've built structures that are pinned in place rather than bolted, so that we can remove things quickly. Quote:
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Re: pic: FRC488 - 80/20 Drive Train
Elegant in its simplicity--very nice.
Is this to be used as a test bed for trying new ideas, or do you think we could see Team Xbot using this in a future competition robot? I only ask this because of the additional weight of an 80/20 frame and fasteners, along with other issues with the potential of loosening fasteners. |
Re: pic: FRC488 - 80/20 Drive Train
Hi Madison,
It was great meeting with your team at the Microsoft complex last year. I must say other than the competition itself, it was the highlight of our Oregon/Seattle trip. I am sure you know what you are doing when it comes to your frame designs as we have seen your work and this is really directed at teams in general. Anyway, our team has been using the Bosch Rexroth extruded profile system (similar to 8020) for 7 years and except for the fact that the profiles are a bit heavier than the equivalent size 1/8" wall square or rectangular tube, we have nothing but good things to say about it and have learned over the years how to exploit its features making some pretty spiffy lifts and robot frames. One thing we really like about the Bosch system, is that the rotating T-nuts drop in from the side and have ribs that bite into the profiles making them less prone to slip which is a problem that was brought up in this thread. Slipping T-nuts have been a rare problem for us and our machines have taken a lot of hard hits over the years. Also you can premount the T-nuts and screws to the component itself, and drop it in along the extrusion at any point. 8020 has a much larger selection of accessories than the Bosch 1" system and in all fairness we have never tried them. 8020 also has a drop in nut but they are different and if I am not mistaken, they have to be rolled in unattached to the component you are trying to mount and cost something like $2.69 each compared to the $0.60 Bosch unit. Not trying to knock 8020, it is a great product. Many teams use it with great success. If you are worried about the T-nuts slipping, you might want to give the Bosch units a once over. Hit them hard enough and they will move too, but I believe the ribbing really helps keep them in place. Alan |
Re: pic: FRC488 - 80/20 Drive Train
I'm posting to this a bit late, but we've used a similar 8020 setup to this for many years, so I thought I'd add some notes.
You may find that there's a lot of corner to corner twist in the frame alone. When you add any upper structure, it greatly stiffens it up. But, the 1010 extrusion, and especially connectors, leave a bit of stiffness behind compared to a welded 1" x 1" tube frame. (This is a similar problem with the kitbot chassis) The bearing blocks, while convenient to use as tensioners, are always a nightmare to keep aligned. When you need to switch wheels, you'll need to un-tension the chain, remove the shaft, and reassemble after. It's not so simple. In our experience, even when you think you have an aligned wheel and axle, it's still not perfect. We've thrown more 35 pitch chains with a similar setup than I care to admit. I've always found approach angles to be difficult (re: shallow) when you have a minimum of 1" of frame in front of the wheels. There aren't too many ways around this issue when using a frame like this. Carefully plan out where you'll be adding extra mounting points, and pre-assemble some T-nuts into the rail. The drop-in's are a pain, especially when you need to line them up with the mating component. 8020 makes some T-nuts with a set screw, to hold them in position. I highly recommend those on any vertically oriented channel. One last note, when cutting 8020, always square off the edges. Chop saws work well, as do milling machines. A band saw, however, does not. Finally, for all those weight conscious folks... The 8020 brand, 1010 extrusion is within 2% of the weight of a 1"x1"x.125" aluminum tube. The bending stiffness is also withing 2%. Torsionally it's not quite as good, but a frame doesn't see the twist like an arm/appendage would. The connections are the key, and using the double-anchors on all corners are your best options (and lightest weight...) While the connectors do add weight, you're talking around 1-2lbs when done correctly. Using the proper material for your upper structure is the key to weight savings when using 8020. Simplicity in design and manufacturing is always good, especially if you can make it as reliable as a highly machined and labor intensive chassis. I highly recommend building a practice bot and (literally) shaking out all the issues. Oh, since we only build one 8020 frame with the new bumper requirements... Figure out a way to mount the bumpers prior to week 6. Best of luck! Bengineer |
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