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pic: Practice Mecanum Chassis
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Re: pic: Practice Mecanum Chassis
Whoa, nice work.
Are y'all planning on using a belt drive for the wheels, or is that just a placeholder? |
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Can you post a close-up of the transmission? Unless I'm a victim of forced perspective, it looks like a right compact number. |
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What is the purpose of that third sprocket? Sensor perhaps?
Why exactly are you using an AM mecanum anyways? Didn't you make some really neat mecanums earlier this year? |
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What program is that modeled in?
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I'm using AM's wheels because the wheels I developed do not belong to me. They were also far more expensive to manufacture. Quote:
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what motors are you going to use?
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Wow that is some amazing modeling...what was that done with....looks very cool and promising
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Almost looks real. Great CAD. Good luck with your mecanums.
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wow ... thats really good!!
[edit] Are they the AndyMark Mecanum wheels? [/edit] |
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From picture description: "This is a look at what FRC488 is planning to prototype this Fall thanks to AndyMark's new mecanum wheels." |
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What's the purpose of the large plates on either side of the wheel? Why not a much smaller system to mount the wheels and/or bearings?
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Wow, great work. Thats an impressive model. I have one question though, do you plan on putting a suspension on you chassis? I can tell you from our experience with mecanum that constant contact is important. Our team, 40, used rubber bumpers on our wheel pods to keep contact. Also at nationals we saw another team (I'm terrible at remembering team numbers) who used small pnumatic pistons for a suspension.
Looks wicked cool though, Good luck! |
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The design I've made previous to this included a more substantial, pivoted subchassis for the two rear wheels that would dynamically stabilize things, but it seemed a bit like overkill. That's shown below: It's an older model, so there're no chains on this one. They didn't disappear or anything. |
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wow that looks cool! im also doing a vex assembly in solidworks.. but doubt it can turn out so nice...
where u ge the macanum wheel part frm? wonder anyone has omniwheel part for me to import :S |
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:) |
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Unfortunatly we don't have any pictures of the wheel pods up close, but I'll give my best try to describing them. With both systems I mentioned before, one end of the wheel assembly must be on some sort of hinge or pivot (we did this with a removable steel pin). The other end of the wheel assembly was held by screws going through the ridge part of our frame, and threaded into the wheel assembly with cylinders of gum rubber inbetween the frame and wheel assembly. A similar system was used, only with 3 inch pistons at 45 degree angles. The other method of suspention you can use (as I belive you alluded to earlyer) is the system team 190 used in 2005, where the wheels were ridged, but it was there frame that actually had one big pivot in the middle. Hope this helps! |
Re: pic: Practice Mecanum Chassis
116 found in 2005 that contact was incredibly important with our holonomic drive (I'd assume it would be the same with a mecanum). Even the very small elevation change of the plywood triangles in front of the loading stations caused problems, as one wheel would lose contact with the ground. (If we drove "North" corner first. Once the North corner was raised happened, either the "East" or "West" wheel would lose contact, as the robot had a slight tip to one side to rebalance itself, which was problematic, as the East and West motors are needed for movement on the North/South axis). We had a system where we could adjust the wheels relative to the frame, but it wasn't active, and it couldn't be done on-field. So, even the slightest imperfections can cause problems if you don't have some sort of suspension system.
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It seems like you could make a flexible enough frame to avoid having to do suspension.
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Also, when team 190 did this in 2005, they ended up spliting their chasis in 2, so that the back two wheels swiveled, somewhat similar to your design.
I didn't have the opportunity to actually see them in action, but they did describe it well. |
Re: pic: Practice Mecanum Chassis
868 used a pnuematic suspension on their mechanum drive, for the purpose of lowering their entire base, not just keeping contact- to my knowledge. But I'd imagine their design might help you with your design problem if somebody's got a good picture.
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Huzzah! I found a picture of our suspension. The black plastic circles were eventually replaced with solid rubber. Its a little hard to make out but the hinge is near the vertical bar on the left side of the image.
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I assume the rubber circles were attached somehow--does the movement of the module affect how the robot drives? |
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Awesome design. Nice and simple. There are a few improvements I see possible. Using 25 chain instead of what appears to be 35 will save some weight, because it will allow you to achieve a smaller pitch diameter on the drive sprocket, which will allow you to use a small sprocket on the wheels to maintain the same ratio, resulting in less material in sprockets and a shorter length of chain. Also, the rollers on you mecanums are all aligned in the same direction, and last I checked, they should oppose eachother to actually achieve omnidirectional motion. That's just a small detail though. Also, I'm a bit concerned about the chain on the rear wheels, since when the wheel assembly pivots, the chain will be forced to twist in a bit of an unnatural fashion. Other than that, the design is amazing in the lines of simplicity. And I like the green AM mecanums :p
[edit] I just realized that AM doesn't have the .step for both left and right wheels, so ignore my comment about the direction of the rollers. |
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I was afraid that an active suspension would be necessary. :) While certainly not too hard to achieve, the added complexity and additional weight hurts the practicality of the design. On your chassis, were the bolts that ran through the rubber cylinders riding in slots? It seems like they'd need to because the module pivots on the opposite end, but it's hard to see from the photo you posted -- which is otherwise enormously helpful. For as much as people are fascinated by these drives, I can't seem to find very many photos. :) Could you describe a bit more about what you mean by 'aligning' the drivetrain? Quote:
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Thanks for the continued discussion everyone. :) |
Re: pic: Practice Mecanum Chassis
man this is getting exciting, I've never experienced mecanums before.
any way to flip the step import in solidworks? As for the suspension, usually how much vertical movement would be enough to keep the wheels on the ground? Looks like the rubber is sufficient, but that depends on the overall weight of ur final bot right? I was thinking of a pneumatic suspension where the pressure applied on each wheel could be adjusted as required (maybe not on-the-fly). anyone done that before? |
Re: pic: Practice Mecanum Chassis
Perhaps an active suspension can be implemented without too much redesign.
![]() When totally locked down with the spacers you've designed in, I believe that this could be strong enough to give you what you want. It appears you're using 1/8" or 3/16" stock- maybe an upgrade to 1/4" would give you all the strength you need there. I would think that if you got hit really hard, the ability of the mecanums to slide would keep you from bending the modules. The chain would still be an issue though perhaps. |
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then again, how much distance of movement in the suspension is required to keep all wheels on the ground? |
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I'll post another screenshot as soon as I clean up the new iteration a bit more. |
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So I've rebuilt things to include a pretty simple suspension, just as team 40 used. I've watched a bunch of video of their machine from Boston and I'm happy with what I see, so I see no use in reinventing the wheel. I also like how easy it ought to be to vary the diameter and type of material used for the suspension based on our experiences. The yellow bolt represents the pivot point that will mount this assembly to the frame. The suspension piece will react against the channel present in the earlier iterations. I'm now trying to adapt the transmission design to this self-contained module so that the chain remains in relatively constant tension during operation. It's not been fun; not because it's particularly difficult to accomplish, but because everything I've tried so far has been pretty ugly. |
Re: pic: Practice Mecanum Chassis
I like the design, I cant wait to see the finished product!
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Are you sure bending the chain back and forth is a good idea? Especially when changing directions rapidly?
Wouldn't it be safer to somehow include your motors and idler sprockets in the wheel pods? |
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Perhaps you can save some trouble by integrating the gearbox into the inner plate of the mecanum assy, and replace the sprocket with a gear, to eliminate the issue of tension all together. I don't know what capabilities your team has when it comes to milling out excess material in the gears, but if worst comes to worst, you can design a nice lightweight gear and outsource it to sdp-si. I'm not a fan of outsourcing in FIRST, but in the real world, outsourcing is useful, and if you don't have the machining capabilities, you have no other option. It's a very nicely designed module. Keep up the good work.
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The latest iteration follows; and please note that I'm dissatisfied with how ugly the gearboxes are. I neglected to color the pivot in this shot, but it's the long 3/8" bolt sticking out from near the middle of the image. The blue represents chain -- #25 this time around rather than #35 helps to achieve some tighter clearances. The ratio as shown is 12:40 in the gears and 18:72 through the sprockets for an overall ratio of 13.32:1. I'm pretty confident this will be on par with or lighter than the kit gearbox arrangement that provides a similar 12.75:1 output. |
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