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chassis ideas swerve
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I really liked how 1717 drove this year. So I am trying to improve on the chasis I saw this year with some guess work since i didn't get to really dive in and get to know it. pnuematic super shifter chain linked to drive shafts and window motor chain linked to drive collar. Electrical bay on the botom. 1/8 aluminum rivitied together. Assum the total chassis weight is 25lbs with rivits.
Is this about right? Would you use banenot motors instead of window motors for steering? Is the super shifter gear box over kill? How much pushing power would this have? How fast would this be with 2 or 4 cims? |
Re: chassis ideas swerve
I would not suggest using banebots on your steering. They have a tendency to short circuit and cause your robot to time out in matches for about 30 seconds. Putting them in the drivetrain would just worsen this problem because they would be exposed to a lot of debris, which is the cause of this problem. it's really easy to fix the shorts on the banebots, but they would be difficult to access in your drive system and you would have to fix the short every match because of the level of dirt and debris they would be exposed to.
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The gearboxes? The motors? The entire package? The 2 main issues with banebots is: -The gearbox blowing itself apart on high reductions (ex: 256:1) -The 775 case shorting (not the 550/540/395) -RC |
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I was referring to the case shorts on the 775s. Our team experienced many problems with the 775s on our arm at our later competitions this year. Team 2056 showed us a method to fix the problem by attaching the positive battery lead to the positive terminal, and the negative lead to the case, and then moving our motor. That seemed to fix the problem, but it was still pretty consistent. The problem would be more apparent if the motor was on the drivetrain, which would be time consuming to fix after every match
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Everyone on 1717 was super nice about explaining their robot and actually showing us up close how it works. I was totally impressed!
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Re: chassis ideas swerve
Stricly speaking, the maximum speed would vary upon any gearing / sprocket + chain ratios.
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Oh, and swerves can push. They just tend to try to avoid pushing matches by using their mobility. |
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The pneumatic parts you see are for their shifters. They put the shifter mechanism on the opposite side of where the Andy-Marks are placed. I don't know the full story behind this but I have a hunch that they did this because originally they were going to have each CIM have its own gearbox and each module independently steered. From my conversations with one of their mentors, they choose not to go that route to conserve two banebot motors. So they have two CIMs for each gearbox So the belts you see by the pneumatics are for drive and the ones the cross are for steering. The drive left wheels together and right wheel together. For steering, the front right wheel is connected to the back left wheel and vice versa. This means to rotate the robot, they have to come to a stop but they specifically designed their robot to minimize the need to rotate. For my opinion, you can get away with a standard andymark shifter. The supershifter has a extra gear reduction you don't need. You will defiantly want to use all 4 CIMs if you want to cover the field as fast as 1717 does. Another great team to look up is 1640: wiki.team1640.com/ |
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Both motors work for steering. Really I would suggest using the window motors if only because we have a very limited amount of high power motors (CIM, FP, BB) and using 6 of them in the drive train may not be the best use of those resources. I have only ever seen 1 shifting swerve drive and that was from 118. Check for their 2007 video if I recall. Aside from acceleration I don't really see a point in doing that. Swerve systems are more mobile than many other platforms. This allows them to drive around obstacles rather than pushing through. Unfortunately I don't see many teams using them this way. As for how fast it would be, perhaps take a peek at JVN's mechanical design calculator. Now, the part you didn't ask for... If this was just a thought experiment then cool. From what Akash has told me about 3553's resources, and from my general opinions of most teams, doing a swerve drive isn't the best option in my opinion. I would feel that mastering a 6wd style base would be a very good use of time and resources. Train some phenomenal drivers and make it bullet proof. The key to a successful season is a robust and reliable drive system. Additionally, swerve systems require massive allocation of resources including driver practice (meaning you need 2 bots) and programming. The software for a swerve system is difficult and, if done wrong, can result in your system being unusable or not performing to your expectations. The above being said, if you decide to go this route I will make two suggestions: Prototype in Vex/FTC/Any Other Small Scale. - I cannot stress this. It will save thousands of dollars and most of the concepts will apply at the large scale. Build two robots. - Driver practice is key with swerve, you can't just point a direction and go, there is a delay. If you need any help (I'm not an engineer, just a programmer) Akash has all my contact info. Hope to see 3553 out on the field next year. |
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As explained, you can see the left side and right side are both powered from 2 cims each on a 2 speed gearbox. The two cross belts control steering between left front/right rear and vice versa. Mark, could you explain why they would need to stop to rotate? From watching their matches on Curie, I never saw them really stop moving. I haven't been able to find many videos, but you can see them here: http://www.youtube.com/watch?v=n63CaX1W-pU (the red alliance robot with the black lift) (Team 126 is looking into building a similar drivetrain for the off season) |
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In this thread, I asked them to post more pictures of their 2010 robot. http://www.chiefdelphi.com/forums/sh...ad.php?t=84838 Essential when rotating clockwise, let's say the right side drives forward and the left side reverses. Because the pivot action of the drive modules are actually connected front left to back right and vice versa, each sets rotate in opposite directions. Therefore the right side modules are actually facing opposition directions when rotating despite being driven from the same drive gearbox. I hope this explains it, I finding hard to describe the motion. I have also observed that they engage the rotate motion very quickly and almost seamless with their driving. Perhaps this is due to their fast gearing in both drive and pivot. Our team is also looking at 1717's drive train for next year, I think we will CAD it before we start asking ourselves if we actually have resources to pull it off. It would be competing against a new 6 wheel drive concept that emphasis on durability and ease of repair. |
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That complicates things a bit. Now i could see why this drive gets heavy. Going back to my incorect observation about pnuematic motors. Has anyone ever used them to control low torque rotation applications. This could be a way to have 4 individual drive motors while keeping the weight down. Thanks |
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As to the banebots vs. Window motors, we've actually used both to steer our swerves (windows in 2010, Banebots in 2011). We had a few problems with both, but the Banebots definitely served us better.
With the Window motors, running 1 per wheel module (#35 chain, 15T to 15T), we suffered from their incompatibility with Jags until we removed the locking pins. If you do this from the start (and personally, I'd avoid Jags unless you're CANing), you might be fine. With the Banebots (RS-540s, 256:1 planetary gearbox), we never had a problem with the motor, but the gearboxes loosened up sometimes. This was likely simply a product of our mounting, since we stole 2 of the attachment points to mount it to the pivot. Great motors, but it's hard to give them up to the drivetrain in some cases. |
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Here is an updated model. Based on ththe comments from this thread and http://www.chiefdelphi.com/forums/sh...threadid=95088 i am going to create to more concepts. I will also incorporate the banebot motors into one of the concepts.
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I have contemplated using pneumatic motors since FIRST has open up the pneumatic rules. They appear to be not used for precision motion. Pneumatic valves, simply can't move fast enough. If you found a pneumatic motor small enough to use on a first robot, perhaps it would be better to replace motors elsewhere so that you can use extra motors on the drivetrain. Maybe, rework a pneumatic screwdriver or grinder? That would make a pretty funny roller claw. |
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