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pic: Prototype Drivetrain v2
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I would recommend powering all of the wheels that will be in contact with the ground, including the Omni wheels. In addition to that, are you planning on using the custom traction wheels shown in this model? If so, do the spokes require 3D contouring?
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could you possibly design a suspension that could keep a chain tensioned? Possible have it move around a point that would have the chain stay tensioned as it goes up and down?
Or could you have a chain tensioner that keeps a chain tensioned by use of springs and have the springs that hold the chain tensioned be easier to compress/expand than the spring or whatever you are using to make the wheels have suspension. I am trying to design a suspension for our robot next year but the wheels would be powered in one way or another I don't see a point in having a suspension if you are not going to power the wheels. What is the reason behind having a suspension on unpowered wheels? |
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Why exactly do you need suspension?
Wouldn't it be much easier to lower the center wheels by about 1/8" and power the other wheels with chain? or just going flat 6WD? |
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The suspension is there to improve handling, much like a rocker, only smoother.
I was thinking about widening the carriage for the suspension and putting a dual sprocket with a bearing on the dead axle that is the pivot point. Then run chain to the omni. |
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And if you want it to rock, why don't you just drop the center and forget about the suspension? If you want to still have the suspension, you could either do what you suggested or make the suspension go up and down along an arc with radius equal to the distance between the front and middle wheels, so the chain has a constant distance. |
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There is currently no rock at rest. Once you begin moving the suspension absorbs any jarring movements like sudden stops or turns, making it handle more smoothly. |
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Don't get me wrong, I think your idea is really cool. It's just the matter of seeing if all the effort to get it to work is worth it, and if the benefits are true benefits. |
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The other option would to be have a long arm pivoting on the center axle, but that might be too heavy/bulky for practicality. |
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With springs tensioning the suspension, it will rock only as far as it needs to. Using a diff. eq. we can figure out the specs on the spring. Ideally, at rest, the spring keeps the wheels exactaly level. Once the robot starts moving and the CG "shifts" the springs will expand cushioning any sudden blow (like a rapid acceleration). Additionally, if this robot starts to get flipped, all wheels can stay on the ground providing some traction. The front ones would lift off the most, increasing the Fn on the rear and center That still leaves the problem of chain runs though. I'm not sure a slot would have low enough friction, plus the exterior has to be smooth for the bumpers. |
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How about this: Run the chain so that it is long enough to handle the longest dimension, and stick a couple of McMaster part 5896K1 in there as tensioners. That should help keep the chain tensioned correctly, if you don't have too big of difference between longest and shortest chain runs.
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Do you have any experience with whether or not these fall out or how they work? I don't see how they could tension in a situation like this. |
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Not these--they go in the chain, and don't contact the robot frame at all. Should be negligible effect on the suspension.
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Forget the suspension if you are not doing two things:
Driving over rough terrain like the bumps Powering all wheels You speak of a "smother ride" and I really do not understand what it will benifit you. If you are concerned about your electronics mount them on a foam surface, or some other kind of protection. If you don't want to jostle the rest of your bot, well, almost all of the jostling comes from collisions, not deceleration from turning and stopping. Also if your bot cam into any kind of pushing match it would distinctly be in the featherweight class. Not only will the omnis make it so that you well be easily spun, the 4 useless wheels will give you significantly pushing power. On your v1 thread you mentioned that you mechanical guy said he could put 75% of the weight in the center. I do not see how that is possible when you don't know what next years challenge is. Here is one way to keep the chains in tensioned http://www.flickr.com/photos/47595136@N03/4592232432/ http://www.flickr.com/photos/47595136@N03/4591612471/ http://www.flickr.com/photos/47595136@N03/4591612485/ Power the middle wheel run chain to the other axles, and then add a suspension to the angled bars with closed pneumatics. |
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As for the weight distribution, that 75% was assuming the CG was in fact in the geometric center of the robot, and it usually is pretty close to that. This whole concept may never get built. This is just to inspire the younger designers that I'm training over the summer and to provide us with a jumping off point for next year's challenge. If there is a surface feature like a large washboard or uneven, low steps going up to some important game piece, the suspension will be useful. |
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Your team doesn't like pneumatics? That makes life harder. The same idea works with springs, they just may wear out and cannot be adjusted.
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Any ideas on how I could tension the chains in the current configuration? |
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It seems foolish to throw away a useful tool.
And simply no, I do not see a good way to tension it like you have it set up now, mainly do to the fact that springs in a tensioner will allow chains to slip. Something like this could be converted into that tensioner from mcmaster mentioned earlier. I have never used this style to tension, I have no idea how they work. http://www.mcmaster.com/#sprockets/=70knoq The link isnt working here is the pn 6793K19 |
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I am unsure of why you are so set on a suspension. Quote:
My advice: a suspension is not worth the hassle (and relatively useless) unless you are powering all wheels, or going over a surface that is not flat. To compensate for the sudden stops and starts, perhaps you could try to scale the acceleration and turning to your discretion through programming. |
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I personally like the suspension even if we have a flat surface. Last year the field was flat but at nationals we kept having issues with one or two wheels not touching the ground because of our pick up mechanism which had to touch the ground. There were bumps in the actual field which caused our pickup to touch the ground but our front two wheels did not. I am designing a suspension so this does not happen to us agian. We were using 4 Wheel Drive which is different but the idea is still the same. My design will be for mecanum.
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woah, if that only weighs 30 lbs then something is wrong, a cim in a 1-12 bane bots gear box weighs 12 lbs, there is no way 2 cims and the whole rest of that is under 6 lbs:ahh: :ahh:
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There is also a new post with the tensioning solution for you guys to look at. |
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Confucius say: Man who think physics is religion must sit in own pew. ;) |
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http://www.chiefdelphi.com/media/photos/35715? Already got the tensioning down. I prayed to the physics gods, and they answered!! |
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You could do a dovetail mount. It would take some machining, but it would probably work. Something like the image below (= is the axle).
__ __ =| ||=|| |= |
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*curses at VB's not putting spaces in right*
If you've ever seen a dovetail joint, it should be fairly simple to figure out. Look at a standard door hinge; that's a fairly common dovetail application. Now replace the pin with an axle, and the screw plates with swing arms. You'd need to change the geometry and check the stresses, but that's pretty simple to do. |
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/_\ or \_/-\_/-\_/ with the dashed part cutout and bottom line at the top |
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Either way, I was referring to the door hinge style. |
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So I would make a tenion joint between the carriage and the shaft? That doesn't make sense... Or between the carriage and the side plate? I think a better graphic would help the most honestly, I don't want to place any extra work on you though, but if you could I'd love to see your way of fixing this problem. |
Re: pic: Prototype Drivetrain v2
Door hinge is still the best description I can come up with.
For modeling, take a door hinge and replace the plates with arms of the length you'd need. Replace the pin with the axle. Note that some geometry would probably need to be changed to accommodate robot dimensions and stress. |
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