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#16
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Re: pic: Drivetrain Concept
The center wheel uses a rod running vertically through the side cross pieces of the frame and the 1/4" aluminum plates. Four springs would attach to a tabs on the top gusset of the cross piece at each corner and the bottom attachment plate on the center wheel module. The plates should flex a little and allow the wheel to maintain constant contact with the ground, and because of the springs, there would be little force pushing up on the cross pieces to bend them, but it would probably be better to change at least one set of the cross piece gussets to 1/4".
For the outside U channel pieces, I was planning on using a structural bumper mounting system consisting of long pieces of box tubing bolted to the frame along its entire length, which would be attached to the plywood of the bumper. This would essentially turn the outer frame pieces into pieces of box tubing without adding the extra weight. For the inner frame pieces, I will switch them to the .1" Vex tubing or 1/16" tubing. How much would increasing the length of each leg of the T shaped gussets on the frame increase the rigidity? It seems like that would improve the rigidity by a fair amount, but I have not made a frame using gussets before, so I have no experience with that. I was planning on adding some kind of spacer between the two side frame pieces, but I want to be able to easily remove the outside piece to more easily take off CIMs and wheel modules, so I haven't come up with a good way of doing that yet that wouldn't require sheet metal or welding, which we can't do. To make the wheel module shafts easier to line up, I was planning on latheing down the ends of the shaft to slightly under 1/2" and rounding the edges, then using round bearings. That would cost less and be easier to line up. To change the maximum speed of the drive, I would just change the ratio using a different reduction in the sprockets. Since we will hopefully try building this drive before the start of next season, I wanted to make it easy to adjust so that we could try different confiurations and possibly adjust during the build/ competition season if we needed to. I set the speed at 20 fps because it seems like it would never be reasonable to gear faster than that. The CIMs do not touch any of the bearings (that's one of the reasons the gears are the size they are), but if I were to use smaller gears, I would lathe down the end of the gearbox shaft to 1/4" or 3/16" so that the bearings could be smaller (that's what I did on the center wheel). Hopefully, we will actually make this drive, so a lot of the design is based on our machining capabilities. We have access to CNC/ manual milling machines at our sponsor's shop, but in house, the only metal working stuff we have is a drill press, a small lathe, and a horizontal band saw. Last edited by echin : 30-06-2014 at 07:56. Reason: poor wording |
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#17
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Re: pic: Drivetrain Concept
Not in my team's current design, we have a Cim and a MiniCim powering the wheel, and a bag powering the steering. the whole thing is 4cims 4 minicims, and 4 bags...
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#18
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Re: pic: Drivetrain Concept
I would reach out to teams who have built an a drive with perpendicular wheel(s) to hear their perspective. At least from watching robots with them in the past, they didn't seem to use the sideways drive much to make it worthwhile.
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#19
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Re: pic: Drivetrain Concept
Just be aware that this configuration would be illegal under the 2013 and 2014 rules. You're allowed to use up to 4 total of either mini-CIMs, BAGs, or a combination of the two. You weren't allowed 4 of each.
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#20
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Re: pic: Drivetrain Concept
How many teams actually use a H drive? I know that 624 and 148 do, but how many others are there? From watching match videos of these teams, it looks like they primarily use their center wheels for getting out of defense, but do not use them continuously.
Also, has anyone ever tried using a CIM as part of a spacer? If it was possible to mount something to the outside frame piece that touched the back of the CIMs, it would act as several large spacers and make it much more difficult to bend the frame in. |
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#21
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Re: pic: Drivetrain Concept
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#22
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Re: pic: Drivetrain Concept
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51 did an H drive in 2011. 217/148 did a similar drive in 2010. I'm sure there are others that I'm forgetting. |
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#23
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Re: pic: Drivetrain Concept
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#24
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Re: pic: Drivetrain Concept
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#25
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Re: pic: Drivetrain Concept
I'm almost done with the next revision and I'll post a picture when I'm done (I'll be gone for the rest of the week so it might be a while). I changed the center wheel to a pivoting piston actuated system instead of linear spring loaded, which saves some weight. I also removed the back wheel module and changed the drive to something more like 624's grasshopper drive. This requires the drive to tip at an extreme angle to use the traction wheels and only saves a little more than 1 lb, so I may change it back to more like what I had before.
An H drive would be able to drive like a swerve with some fairly simple programing, so why does it seem like most teams using H drives don't drive them like swerves? |
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#26
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Re: pic: Drivetrain Concept
We experimented during build with field-centric drive controls for our H drive. The difference in power between the X and Y drive directions meant that it wasn't particularly useful because the robot still needs to be pointing forwards to go at any decent speed for travel. Also, our team specifically isn't able to get access to a decent-sized area for driver practice very often, so the additional time needed for our driver to get used to it didn't seem worth it.
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#27
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Re: pic: Drivetrain Concept
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#28
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Re: pic: Drivetrain Concept
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#29
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Re: pic: Drivetrain Concept
So basically nonadrive but without gearboxes?
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#30
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Re: pic: Drivetrain Concept
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Last edited by randantor : 12-10-2014 at 23:17. |
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