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pic: Four Speed Three CIM Gearbox
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Re: pic: Four Speed Three CIM Gearbox
What advantage(s) do you expect from having a four-speed, 3CIM gearbox over a two-speed 3CIM gearbox? A four-speed 2CIM gearbox? Heck, even a single-speed 3CIM gearbox?
Basically, why? This seems like overkill. |
Re: pic: Four Speed Three CIM Gearbox
And for the 2016 FRC game, OVERDRIVE 2: OVERKILL. This game is played on a 10 meter by quarter mile field in the streets of Miami. Any robot to get to the finish line in 10 seconds wins by default and gets a free ride to champs!
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Ever considered taking that third and fourth position and turning it into a PTO? That wouldn't be very important in a game like 2015 whatsoever, nor a game like 2014. But, for example, in 2013, 254 used a PTO to power their awesome climber. |
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It looks quite well done for the project. It's not useful for competition, but it looks good anyway. :P
Nice render too. For the top shaft of the gearbox, instead of using a hex bearing, I would round down the end of the shaft and use a round bearing. If you only have 2 standoffs going to the mounting plate, I would change it to 3-4. EDIT: +1 on the PTO idea. |
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To me, the big "why" is why have four speeds over about a total 3:1 high-to-low ratio? If you're going to bother with four speeds, spread them out a bit wider!
At a minimum, I would put the shifts a factor of 2:1 apart, resulting in an 8:1 overall ratio from high to low. At a "standard" 2.56:1 ratio between shifts, the total range would be 16.77:1. At 3:1 per shift, it would be a massive 27:1, which could be a real game changer in some highly defensive games or games with steep ramps. Especially if you want to reserve some CIMs for manipulators! |
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Thanks, yeah I know it's really overkill. So basically to answer the question of why I decided four speed, my team is working on the summer design project thing that was put out a couple weeks ago. The end game involves chasing down a mini bot on the field, so the end game team wanted to be able to travel at the mini bot's speed (~13fps) to line up with it and a faster speed to catch up to it. We also wanted to be able to move around a little slower with more control for adjusting shots and in case anyone wants to push us. I know we could've gone with a two speed and controlled the speed with code, but that's what the team decided to go with. Also, it gave me a nice challenge which is always fun.
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Hehehe..been done already sort of... https://youtu.be/efvCDYTj0Wk |
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Impressive Design! Team 368 made a 4-speed transmission in their 2005 robot, IIRC also. Cool stuff! |
Re: pic: Four Speed Three CIM Gearbox
Sorry for me asking, but what is a PTO gearbox?
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Lifting oneself in 2013 could be accomplished using all 6 cims in a drivetrain, for example. |
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This is really cool. If you can find the machining resources to make one I would totally do it as an off-season project. Sure it may not be the most practical thing for the competition season but you'll learn a lot while doing it. You could also design up a 2 speed variant and make that too and do a comparison - maybe even post a white paper so we can all learn about it. Good stuff!
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Assuming your robot was geared for 18 feet per second in high gear, and 0.67 feet in low gear (a 27:1 spread), you'd need to have a 1800 lb robot (or group of robots) to take advantage of the gear ratio and never trip the breaker in a pushing match. If the robot weighed any less, you could get away with a smaller spread and never worry about tripping a breaker. That sounds like my kind of game!! :D |
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Don't think of it as a 6-CIM drivetrain, think of it as a 6-CIM powertrain, powering three very different motorized mechanisms in an extremely effective and efficient manner. Many ways to skin a cat. |
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Although what advantages would it serve to have power coming from the same place if you could just use more motors for a different mechanism? The only reason I can think of is because there is a limit on the amount of CIMs you can use and it's hard to get that kind of power from other motors, so for climbing or stacking you'd want to be able to tap into those motors. But for example there wouldn't be much of an advantage from using a PTO to also power an intake system that could easily be powered by a smaller motor. It would actually be kind of wasteful. |
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And, for the record, my prediction: The first FIRST team to execute this sort of PTO will join 71, 118, 254, and 1114 as one of the top five teams of all time (unless, of course, it's one of those four who do so). |
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Second of all, the ultimate PTO would use every motor available and just shift however many motors necessary to any function. (However you'd have to have some crazy programming scheme or something to keep from browning out like crazy) I also think the first team to do this won't be one of the greats; I think the first team to try it won't get picked at their event. That's insanely complicated, even for a team like 254 or 118. I would love to see someone do it successfully though. it would just be a mechanically sick robot to check out. :D |
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And I did mean the first team to successfully execute it, not the first to attempt it. |
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I think you went quite overboard on the weight reduction on the outer plate. A pocketed 1/8" plate with no flanges, especially with the reduction being supported off of the end of the plate past the standoffs like that, will have some issues with flex and rigidity. With gearbox designs posted to CD in general there's often an overemphasis on lightening the plates as much as one possibly can, when it's really not that substantial of a weight savings over a more conservative lightening pattern or even unlightened plate.
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It'd be nice to get a high power, high efficiency motor on FRC legal list. Also, it's simpler for teams just to add more motors and gearing independently than it is to centralize PTO it all. It just doesn't make sense for FRC. |
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Due to weight constraints, we went from a robot that had 6 motors similar to that of 2014 to a robot with only 1 CIM on each side. We started with a 2 CIM 1 Banebot 775-18 on each side, then got rid of the Banebot for several regionals, then finally 1 CIM on each side at CMPS. We did this in order to make weight as we added 1, then 2 ramps and also to add our upper claw to hold the trash can in place while stacking. This game was perfect for having just 1 motor on each drive, considering all we did eventually was make stacks from the feeder station. |
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I often find that at least thinking about (and sometimes even building) the extreme cases leads to ideas that prove useful later. IIRC, the OP tossed this up as a bit of a "blue sky" thread, and I've been treating it as such. Checking back, OP included "probably weighs a thousand pounds" and "I do not actually intend to build this thing." As a result of this thread, I now know to keep an eye out for high power jobs that don't require simultaneous wheel drive. 2013 and 2015 both provided this sort of challenge (pyramid climb and can burglar respectively), so it can't be that rare. It wasn't in my mental toolbox six months ago. Another thing that makes me really like the PTO concept is the addition of a flywheel. It is possible to tap more power from a PTO with a flywheel for a short period than from motors, especially given the new motor brownout situation. I like having a defined brownout over an undefined one, but it will probably be several years before the FRC community learns to take the best advantage of the new opportunity/challenge. At which time we'll switch to yet another control system ;-P> Thinking a bit more, 2014 (Aerial Assault) also provided a PTO possibility with the ball thrower. We had six CIMs on our 2014 robot, two for a "kicker" and four for drive. (We used pneumatics and an AM gearmotor for the ball pickup.) We nearly always threw the ball while stationary, so sharing all six CIMs between drive and a more elegant and powerful launcher might have been an improvement on both fronts, especially as most of our "accelerator" designs would have thrown the ball from higher off the carpet than the kicker did. |
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also on the subject of small motors on drivetrains, I know that 2471 was running their Swerve on a mini-CIM for each wheel by DCMP in order to have more weight for a better can claw & some can burglars, with no discernible difference in performance from when the had a CIM per wheel. |
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... and needed some degree of precision to place scoring objects (inner tubes) onto its scoring pegs. All I'll say as far as it being physical is: Aerial Assist was rough. Now extend and beef up the appendages another couple of feet or so. And "meet in the middle" autonomously...at speed...or under driver control...while trying to score...or block scoring... 118 had a pretty decent swerve the previous year, but for this one they added a pair of F-P motors to a 4-CIM, ran all the wheels off the same gearbox and the same turning motor, and had a turret on top to allow for scoring in any orientation they felt like being in. Basically, lots of push and lots of maneuverability were judged "pretty important" that year. (Though... IIRC, Einstein was a bunch of 6WD skid-steers that year, with maybe a couple of non-tank drives around.) |
Re: pic: Four Speed Three CIM Gearbox
I'm still wondering what was up with that central gearbox that was later distributed. It appeared to be an essentially 1:1 gearbox which brought four CIMs together onto a single shaft, which was then redistributed around on four separate swerve shafts. It seems to me that it would have been easier and more efficient to put a CIM on each swerve shaft, but to include a sprocket which tied the four shafts to the same speed to allow redistribution of energy as needed (e.g. as loading increased on two wheels due to acceleration away from them).
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Another good example is 148 in 2008... they did 2 FP plus 4 Cim, going to three swerve pods, which were steered with a van door motor. Since they had no "front" (it was an equilateral nonagon lap runner), they had no need to "steer". As a result, they could both run laps well AND provide very good defense (and this was one of many reasons why their CMP alliance were champions). |
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I didn't notice the shifter. With that bit of info, the central gear box makes perfect sense. While separate CIMs which are chained to keep the same speed would have also allowed the power generated at one wheel to be used at another, four (or six) shifters would be more complex (and costly and heavy) than the "gear manifold" and a single shifter. |
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