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Mecanum wheels
Hi, I was just wondering what is the purpose of the mecanum wheels, how do they work and are they worth the $400 for the set of 4, also if the sell them somewhere else cheaper than that could you give me the link?
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Mecanums have some nice maneuverability. They are able to strafe, for example. (you can find some videos of it on YouTube)
However, mecanum wheels will be weak for pushing power and can slide around. You'll likely be pushed around a lot on the field if you use them |
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Also make sure you know what size you need. Don't use mecanum wheels just for a cool factor. Mecanum wheels are great for maneuverability, but when it comes to pushing they are worthless. |
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The choice is completely dependent on your team's strategy. Is your shooter reliant on consistent positioning? If so, you may not want to use mecanums because of the pushing issue. |
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In this game the only big advantage I see for them is with catching the ball from the truss, so unless that's a big part of your strategy, I wouldn't get them. Another downside to them is that they're quite heavy.
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Mecanum work well if they fit your game strategy. You can get a full set for much less then $400. Vex pro sells a set of 6" for 159.99 http://www.vexrobotics.com/vexpro/wh...um-wheels.html
Also, in my experience the vex wheels preform much better then the andymark equivalent. |
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Try VEXpro. They have very affordable yet durable mecanum wheels. The other posters are correct in assuming that unless you are trying to catch, mecanums might not work well this year... However don't believe they are easy to push. We had to play defense with our mecanums last year in matches when our shooter failed and were fine. We could block lots of teams. I know this is contrary to popular belief, but a properly done mecanum drive base can in fact be very strong.
For anyone that wants to question our pushing abilites, we have video... |
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Whether or not this translates to "being pushed all over the field" depends critically on context (robot weight, weight/drive of opposing robot, weight distribution, manner in which you're hit, etc). |
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My team has used mecanum wheels for the last three competitions, and each time we had great success with our drivetrain.
The system is meant to give a robot high levels of maneuverability, and when it is allowed to move at high speed, it creates a formidable opponent. Having the range of motion provided by a mecanum drive can allow a driver to jump out of the way of onrushing defenders, all while maintaining a scoring opportunity When discussing pushing and mecanum, it should not be forgotten that the goal of this drivetrain is maneuverability, not brute strength. Due to this, a pushing match with a robot designed for pushing will be lopsided. But that does not mean that this drivetrain is easy to push. I have seen our past mecanum drives stop six wheel drives dead, and win pushing matches. When we use mecanum, we maintain a balance of speed and pushing power, and ensure we are not compromising one for the other. This quote sums the entire discussion up, and is good food for thought. "Mecanum drivetrains, like every other, have advantages and disadvantages" - Mr. B |
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I have a quick question about mecanum wheels. Can they be placed in a trapezoidal configuration?
Has anyone tried this before? How well does it work? |
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---[]----[]--- []----------[] where the [] are wheels and you have the front wheels in narrower (or the back wheels)? |
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I encourage anyone and everyone who thinks that they understand mecanum physics to read the whitepaper given here: http://www.chiefdelphi.com/media/papers/2759?
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Our team has used a mecanum drive train for the last three years and we've had a lot of fun with them.
As the robot driver for the past two years, I can assure you they're wonderful to control, and driving becomes a lot easier with mecanum. :) Controlling the a mecanum-powered robot is a lot like moving a character in a first person shooter video game, which I'd assume many students are familiar with already. Couple a mecanum drive train with gyroscope technology and now your robot can always move relevant to the driver (No matter the orientation), which in my personal opinion makes controlling the robot even easier. While a downfall may be that you lose a lot of pushing power, the versatility gained to out-maneuver the defense matches said downfall quite well. |
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Our VexPro mecanums have held up well. They survived one regional and some off season demos with no problems, and in our shop we typically run them on concrete. We are planning to use them again this year.
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Mecanum wheels are very nice for alignment of your robot even when the driver has not had a lot of practice time. I would imagine this year aligning your robot in order to gain possession of a ball would be important to some teams. Practicing gaining possession in a real-game situation is difficult for a lot of teams, so mecanum can be handy here.
Also, I always throw in my vote for don't believe that mecanum can easily be pushed around. Wait...am i part of the majority on this vote?? :yikes: |
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At the moment, my team is not a fan of using mecanum, unless it is undeniably the absolute and only way to win matches. With mecanum wheels you can lose up to 50% of your power when doing moves like strafing, whereas with swerve drive, all the power is used more efficiently. Mecanum wheels are indeed expensive, and I don't think that they're worth the price unless you are absolute that they are the best choice. From my experience here in the Californian bay area/central valley, the best teams stick with drop center six wheel drive treaded wheels. Why? They are inexpensive, offer the best traction, best pushing power, least complex in programming and build, easy to fix, and provide all the maneuverability necessary. Name one team that has made it to the Einstein field using mechanum wheels. None, because this has never happened in FRC history, but hey, there's always a first, and it could be anyone!
If your philosophy isn't all about winning, then have at it with the mecanum wheels! Mecanum robots are really fun to drive, too. Still, they are a pretty penny, but 100 bucks per wheel isn't a bad deal. I'm not saying that you can't win with mecanum wheels, many regionals have been won by these types of drive bases, but what I'm saying is that treaded wheels in general are a better choice in my opinion. Treaded wheels are also LIGHTER! And that could be the difference between passing and not passing inspection if you cut it really close with your other robot components. |
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There's a bit of mis-information in this thread, and while I don't want to join in the debate, I'd like to set the record straight for any of the newer teams that might be using this thread for information.
Mecanum Wheels can be purchased from two different FRC Suppliers. - AndyMark http://www.andymark.com/Mecanum-s/53.htm AndyMark's Mecanums were first released for the 2007 Season and have been evolving since then. They're offered in FRC relevant sizes of 6" and 8" with a Standard Duty and Heavy Duty version of each. The Pricing Varies from ~$250 for a set of 6" Standard Duty to in excess of $400 for a set of 8" Standard Duty. - VexPro http://www.vexrobotics.com/vexpro/wh...um-wheels.html VexPro's Mecanum Wheels are relatively new compared to AM's Mecanum Wheels, but have proven themselves to hold up reasonably well in the FRC Environment. They're a bit Cheaper than AM's Mecanum Wheels and rely on a primarily plastic construction in place of Metal. As far as Mecanum's implementation in FRC, they're a decent way to make your drivetrain more maneuverable, as well as adding omni directional functionality within a traditional frame. The increased agility awarded by Mecanum wheels should allow you to move around traditional defense to the point where 'pushing' isn't necessarily required. All of that being said, when comparing two similar drives, with the only difference being that one Uses Mecanum wheels in place of a traditional wheel, the Mecanum Drive will almost always have less traction than the traditional drive train. This is due in part to a couple of factors, the wheels always being in a constant state of slip (in that they're applying force in a non-fore/aft direction) being one of them, and the other being that each wheel's motor is independent. This means that if one of your wheels leaves the floor, or starts spinning, you're not only putting down the power of (3) motors. |
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We have used Mecanum wheels the last 3 years with great success.
Great for manouvering in all directions without haveing to turn. Last year we used the 6" dia heavy ones from AM and could push our way around as well as resist being pushed around. It helps if you have a heavy robot though. And it's a good idea to buy a spare wheel or two, but they are expensive. |
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Mecanum wheels have a short history in FRC. They tend to have bad stereotypes as being easy to push around and difficult to control, particularly among individuals that have never used them.
The way people write about mecanum wheels, you'd think they were describing casters on an ice-rink. The easiest drive-train I've ever used in FRC was a set of field-centric mecanum wheels. I've watched mecanum wheels be used for defense effectively, and I've seen times where the maneuverability and ease of use of mecanum wheels won matches. To answer the OP's question, I think $400 is a bargain for a set of mecanum wheels. Whether your team's strategy calls for them is a different question. |
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Could anyone point me to resources about the maximum speed you can run Mecanum wheels at ?
I'm wondering (and trying) to find out if all the gear boxing is really necessary. Once they're slipping they're slipping, and the friction factor for all four wheels would be ~equal. |
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Can anyone speak to the wear of VEXPro 4" Mecanum rollers compared to the 6" wheel rollers over the course of multiple competitions?
In an average year we compete in 2-3 official and 2 off-season competitions, perform in several demos & run a lot of driver practice for the next year's team. So the wheels really need to last. Yet it'd be nice to know what spare parts to get ahead of time (i.e. 1 set of spare rollers per 1 event or 2 events?) when comparing wheels. If we have to replace the 4" wheel's rollers every 1 event, we may go the 6" route so we don't have rollers that are wearing thin at the end of an event. My team's poking at the idea of Mecanum for a few reasons, and it's easy to implement on our current drive frame. About Mecanum in general: The only thing I can say without reading a metaphorical earful from Ether (ha, hi Ether) is that the default field-centric (or robot-centric with no deadband) control algorithm robs the drive train of power just by the nature of the code. When translating on the 45-degree relational diagonal (i.e. 0 degrees = full forward, 90 degrees = full right, so at 45 degrees the bot goes forward & right), 2 motors are completely turned off by the algorithm. If we implemented Mecanum, we'd most likely do a dual-mode driver control. In the first mode, it'd be field-centric holonomic drive. In the 2nd mode, the driver would be limited to robot-centric tank drive with 90-degree strafing. The driver would be in the 2nd mode most of the time. |
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Hi Jesse :-) Quote:
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Mode 2a: Standard 2-joystick Y-axis-only tank drive (X-axes disabled) Mode 2b: Right (or left) X-axis commands strafe (disable Y-axes) |
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Looking at the scoring for this year, a catch is the same as a high goal score (disregarding assist points, since you can score low and get the same assist score), so if teams know you can catch, they will try to defend it. Hitting a moving target is added complexity you don't need. I'd pick a catcher that has no wheels at all before I'd pick one with mecanums. |
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I'll be sure to edit that, though. You won't see a single extra "h" in my post when I'm done. Thanks for the correction! |
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With the 2a/2b mode, just hold a button and do your strafing with minimal deadband. |
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last year our team loved our mecanum wheels. sadly we where borrowing them. this year we are buying them from vex. they are a lot cheaper with similar performance.
http://www.vexrobotics.com/mecanum-wheels.html |
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http://www.andymark.com/product-p/am-0732.htm http://www.vexrobotics.com/mecanum-wheels.html |
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It may be important to be aware that drivers may not have success moving others robots out of the way by turning or strafing, but instead can have success by pushing straight on. |
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You can purchase additional rollers online to replace old/cracked ones. We did this to all of our rollers to retrofit old mecanum wheels and make them sort of new again before last season. If you check the wheels regularly and make sure you have spares on hand you will be fine. |
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Put another way, if the ball is a mere 6" off target, you'd rather have the ball bounce off you (and then have to go chase it) than see a robot with the ability to take a half step to the right? :confused: |
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My point is that the ball will never be anywhere close to 6" from being caught, it will be much farther away and completely un-catchable because a mecanum robot can not hold field position. If your catching robot uses mecanum wheels, pushing it out of the way will be a common and effective defensive strategy. In a game like this where field position is everything, a mecanum robot is at an extreme disadvantage. The only role I can see a mecanum robot playing effectively is a robot that cycles the ball by itself with no assists. As soon as it tries to play a role where it has to stop and wait for its alliance to do something it would lose its field position and ability to add assist points. |
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Having a robot that can be pushed in any way is disadvantageous to being a good target for catching, so I'd say the best pure catcher is a robot without wheels. However, making the trade-off of allowing some pushing in exchange for the ability to move and complete other tasks could be a successful strategy. Toggling between a drivetrain and a traction device would give the "best of both worlds" at the expense of complexity (independent swerve being another solution, albeit even more complex). |
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Designing to be defended against is a really good way to put a ton of work that may or may not see a benefit in competition.
Remember 2006, when 25 had a robot that was solely human fed, and basically shot from the floor? And went undefeated right up through division elimination rounds? Ultimately the benefit of mecanum ends up coming down to what your game strategy is. If it's to be a flexible assist bot, it may very well be worth it-- if it's being a thrower bot, it very well may not be. Ultimately it's all just speculation until we get to competition regardless. Just like any other year, there will be successful 6WD robots and successful mecanum robots. The team makes the tools it uses worthwhile, not the other way around. |
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We're very happy with how that design turned out, and are confident in the durability, especially in a game with a flat field like Aerial Assist. If you jump a robot off a loading dock, will the wheels crack? Yes: Based on our testing... not until the 3rd jump. :) If you slam the wheels into a wall with a rolling robot, will they crack? Not in our testing. I'm confident that VEXpro Mecanum Wheels will stand-up to normal wear and tear during an FRC season. If a wheel breaks, it is likely that the wheel wasn't damaged due to extended match play, but instead the robot was dropped when being loaded into a mini-van. Also, I hope it goes without saying for VEX products at this point: If you have a problem or break, please contact our tech support folks so they can help make it right. prosupport@vex.com I'm especially excited to see teams using our new 4" Mecanum Wheels. This game lends itself perfectly to small wheels, and I believe there are some strategies which would benefit from holonomic motion. -John |
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Is there any information on mecanums wheels and drivetrains? Live Axle vs Dead Axle?
I have never use them and am looking for information. Transmission? Does and one have some good information to share. Thanks |
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Apologies to JesseK and bEdhEd. I was not attempting to say either of you said there was power loss for mecanum moving forward/backward. I was not trying to counter what either of you said, but using your correct statements as an example of the types that are very commonly misinterpreted.
my post was attempting to be pro-active about a future reader's misinterpretation, and was instead itself misinterpreted. I think there is a word for that (other than failure). I guess we can agree that I clearly didn't say it very well. |
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As for your apology, team bEdhEd graciously accepts! |
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So Mecanum vs 6WD and all things being equal I understand most of the pros and cons.
But if you look at the Robot in 3 Days team Boom Done they have 8 motors on their drivetrain - 4 cim and 4 minicim. What if instead of having a straight gear reduction, a team were to use a direct drive shifting transmission such as the Vex Pro ball shifter on each Mecanum wheel with a Cim and Mini-Cim as the input to each wheel? And you took that against a 6WD drivetrain with the three CIM Vex Pro Shifting transmission per side? Does that muddy the water a bit? |
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Do the math and you'll have your answer. This stuff is pretty cut and dry. |
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I hope you have good luck with your mecanum drive this year. Please post back your results! |
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