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Mecanum Revelations for Rich & Duane

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  • Roy ElthamRoy Eltham Posts: 2,296
    edited February 2013 Vote Up0Vote Down
    The plastic used in 3D printing (both PLA and ABS) is actually pretty darn cheap. A 1kg spool can be gotten for under $50. That spool would print out at least a few sets of those wheels. He said he used a hackerspace printer, so it was cheaper by a lot. Even if the hackerspace charged him for material it would likely only be a few dollars. The expensive part is getting the printer itself.

    The plastic on the Rover is most likely ABS.
  • W9GFOW9GFO Posts: 3,736
    edited February 2013 Vote Up0Vote Down
    erco wrote: »
    BUT... they operate exactly like 4 omniwheels in an X configuration. I'll have to build one of those too at some point.

    Not exactly. The main advantage with Meacnums vs omnis (other than mounting in a standard configuration) is that there is no loss in forward speed compared to using the same size of regular wheel.
  • Duane DegnDuane Degn Posts: 10,002
    edited February 2013 Vote Up0Vote Down
    Roy Eltham wrote: »
    The plastic on the Rover is most likely ABS.

    It doesn't have the "feel" of ABS. My guess is it's polystyrene.

    The Rover 5 plastic has the same feel as the plastic used in model airplanes.

    Thanks for the information about he printer plastic. I don't feel so bad for the guy if the parts were cheap to print. Plus, it was probably fun to make one's own mecanum wheels.
  • W9GFOW9GFO Posts: 3,736
    edited February 2013 Vote Up0Vote Down
    W9GFO wrote: »
    Weeks ago I asked about buying a replacement part - they haven't yet replied.

    I posted the above yesterday and today I got a response from MakerBot, three weeks to the day after I contacted them and 20 hours after I complained about it here. Coincidence?
  • ercoerco Posts: 19,188
    edited February 2013 Vote Up0Vote Down
    W9GFO wrote: »
    Not exactly. The main advantage with Meacnums vs omnis (other than mounting in a standard configuration) is that there is no loss in forward speed compared to using the same size of regular wheel.

    Very true, since the omniwheel axle is running at 45 degrees. Square root of 2 over two, so the forward speed is 70.7% of the wheels' tangential speed. Of course that's neither wasted motion nor reduced efficiency, it's more like adding an extra 1.41:1 transmission for lower gearing/higher torque, WRT the chassis fwd/rev axis.

    Overall speed aside, what I meant was that the relative motion of the wheels (and all the associated velocity ratios) for various maneuvers is the same for mecanums and X-omniwheels.
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • W9GFOW9GFO Posts: 3,736
    edited February 2013 Vote Up0Vote Down
    I thing we need a Mecanum/Omni tractor pull.
  • ercoerco Posts: 19,188
    edited February 2013 Vote Up0Vote Down
    W9GFO wrote: »
    I thing we need a Mecanum/Omni tractor pull.

    Sold, and square dancing, too. Don't write those tractors off too quickly...!
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • ercoerco Posts: 19,188
    edited February 2013 Vote Up0Vote Down
    Per Duane, here's a shot of the underbelly with a better look at the hub adapters than the video shows. I'll post another pic of the RP adapters themselves when I get a chance. Basically they fit perfectly into the spiral spokes.
    1024 x 768 - 76K
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • Duane DegnDuane Degn Posts: 10,002
    edited February 2013 Vote Up0Vote Down
    Very nice erco. Thanks for the picture.

    These Vex Mecanum wheels are sure nice. I'm trying to get my Mecanum wheeled Rover 5 to perform a figure 8 the conventional way (as if they were just normal tires). As I watch the wheels wobble around the bent soft metal shafts I'm pretty sure I'm going to want to revamp my Mecanum wheeled bot.

    I'm unsure of what motors and chassis to use, but these Rover 5 bots are getting on my nerves.

    During Pololu's Black Friday sale, I purchased four of these puppies. I've already got schemes plans for the four motors I have, but I'm tempted to get another set to use with the Mecanum wheels.

    The motors on your robot seem kind of loud? Are they as loud as the sound in the video? My wife isn't big on robot noises (you may recall I've switched to solid state relays for devices that will be in the living area (as opposed to have the music of the clicks in the lair)). I'm not sure if using those inexpensive motors for an inside robot would be a good idea if they are as loud as the seem.

    I'm sure I'm going to want encoders on my Mecanum wheeled bot but I'm not opposed to adding them myself. It does make it easier to control the speed if there are adequate tics per wheel revolution. The Rover 5 encoders provides about 333.3 tics per rev which at the lower limit of what I think would be acceptable.

    Anyway, I'm keeping my eyes open for a new home for the Mecanum wheels.
  • ercoerco Posts: 19,188
    edited February 2013 Vote Up0Vote Down
    Yep, they're loud. I'm overdriving them at ~32 volts to get some speed; they'd be somewhat quieter at their rated 24V.

    I still think wheel encoders are fine (as opposed to motor encoders). IMO 32-64 ticks/wheel rev is plenty for most navigation needs.

    The VEX wheels are really great, the only cheesy detail is that silly small square drive hole.

    Hmmm. Maybe I can get a figure 8 as you describe before you do... so much time and so little to do. Wait... strike that, reverse it.
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • Duane DegnDuane Degn Posts: 10,002
    edited February 2013 Vote Up0Vote Down
    erco wrote: »
    I still think wheel encoders are fine (as opposed to motor encoders). IMO 32-64 ticks/wheel rev is plenty for most navigation needs.

    I thought you'd say that. Navigation is one thing, matching speeds is another. Maybe I'm just doing it wrong, at slow speeds, the encoders only catch a few blips per second with the Rover 5 encoders. IMO, it's hard to keep the speed adjusted correctly with so little feed back.
    erco wrote: »
    The VEX wheels are really great, the only cheesy detail is that silly small square drive hole.

    That why drills were made. I used to be timid about drilling out Vex wheels. My three wheeled omni bot still has the square holes in the wheels. I've found it a lot easier to just drill out the hole to the size I want it.
    erco wrote: »
    Hmmm. Maybe I can get a figure 8 as you describe before you do... so much time and so little to do. Wait... strike that, reverse it.

    Too late. I hope you enjoyed your snooze. :smile:
  • ercoerco Posts: 19,188
    edited February 2013 Vote Up0Vote Down
    XLNT. You fell for my ploy. I had no real intentions... :)

    Next, whatever you do, don't mail me $1000.

    I forbid it!
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • Duane DegnDuane Degn Posts: 10,002
    edited March 2013 Vote Up0Vote Down
    Here's an interesting paper on navigation with a Mecanum wheeled robot. It looks like they're using a setup similar to an optical computer mouse to do the navigation since all the slipping and sliding of the Mecanum wheels tend to mess up normal odometery.

    Franklin pointed out in other thread, SparkFun has a new version of a Mecanum wheel for sale. It still doesn't look like it's nearly as nice as the Vex Mecanum wheels.
  • Roy ElthamRoy Eltham Posts: 2,296
    edited March 2013 Vote Up0Vote Down
    I got a set of those new Mecanum wheels from Sparkfun. Very solid and nice. All metal hub parts, nice rubber rollers, and small (similar radius to the old ones they had).

    Much better than before, and I'd say comparable if not better in some ways to the Vex ones. Especially for a little bit smaller bot.
  • Duane DegnDuane Degn Posts: 10,002
    edited March 2013 Vote Up0Vote Down
    Roy Eltham wrote: »
    I got a set of those new Mecanum wheels from Sparkfun. Very solid and nice. All metal hub parts, nice rubber rollers, and small (similar radius to the old ones they had).

    Much better than before, and I'd say comparable if not better in some ways to the Vex ones. Especially for a little bit smaller bot.

    I think the new Mecanum wheels at SparkFun look nice too.

    Could you elaborate a bit on what you like better about the SparkFun Mecanum wheels over the Vex wheels?

    As far as I can tell the only advantages the SparkFun wheels have are size (if you want smaller wheels) and ease of mounting. And I suppose they look better (not a trivial factor).

    Am I missing any other advantages?

    What motors are you planning on using with the SparkFun wheels? Will you be using encoders?
  • Roy ElthamRoy Eltham Posts: 2,296
    edited March 2013 Vote Up0Vote Down
    The main things I like about them is the size, look, and the mounting being better. So basically what you said already. Also, since they are metal, they have a little bit of weight to them which will help them stay in contact with the ground better.

    There is one thing that could maybe be better, and that's the number of rollers. There's only 6 per wheel, so I am expecting the roll to not be as smooth as it could be with more rollers to "round out the shape".

    I was planning to put it on my rover 5, but I think that's still down in SD, so I'll probably end up using some pololu motors I have with encoders. I think encoders are important to getting good clean motion out of the wheels. If you have consistent motors like erco has then it's less important, but typically motors are less consistent.
  • Duane DegnDuane Degn Posts: 10,002
    edited April 2013 Vote Up0Vote Down
    Roy, thanks for the information about the new Mecanum wheels.

    It's good to know these work better than the previous ones sold by SparkFun.
  • ercoerco Posts: 19,188
    edited April 2013 Vote Up0Vote Down
    The VEX wheels are heavy duty and heavy. They may outweigh your entire rover 5 chassis.
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • Roy ElthamRoy Eltham Posts: 2,296
    edited April 2013 Vote Up0Vote Down
    erco,
    I do have a set of the VEX wheels also (the older ones, not the new 6 and 8 inch ones). My comparison of the heaviness was relative to the older ones sparkfun was selling (which are not very heavy at all). If these new ones were as big as the VEX wheels, then they would probably be heavier.
  • ercoerco Posts: 19,188
    edited April 2013 Vote Up0Vote Down
    Wow, those new 6 and 8-inch VEX wheels are impressive: http://www.vexrobotics.com/mecanum-wheels.html

    Of course those are priced accordingly at $120 and $190 per set. The 4" wheels remain a conspicuous bargain at $60/set: http://www.vexrobotics.com/276-1447.html
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • Duane DegnDuane Degn Posts: 10,002
    edited April 2013 Vote Up0Vote Down
    erco wrote: »
    Wow, those new 6 and 8-inch VEX wheels are impressive: http://www.vexrobotics.com/mecanum-wheels.html

    I think it's interesting both the 6" and 8" wheels are available individually. There are also replacement rollers available.

    You save almost $10 by purchasing a four wheel set of the 8" wheels over purchasing them individually but a four wheel set of the 6" wheels will cost you an extra three cents over the individual wheel price.

    I agree their 4" Mecanum wheels are a good deal. I'm glad you suggested I get some (one of many erco inspired purchases I've made).
  • ercoerco Posts: 19,188
    edited April 2013 Vote Up0Vote Down
    Duane Degn wrote: »
    I'm glad you suggested I get some (one of many erco inspired purchases I've made).

    Do not buy erco's 50 stereo jacks for $6. I forbid you. And everyone else.

    Put it right out of your mind.

    I command you.

    No.
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • VEX LAST CALL???!!!

    Apparently the only nice affordable mecanum wheels in town are discontinued. Long gone from the VEX web site listed 3 posts back in this thread: http://www.vexrobotics.com/276-1447.html

    VEX's new wheels are disassemble-able (?) and considerably more expensive: https://www.vexrobotics.com/mecanum-wheels.html

    But the originals are still available for $60/set (same price) at https://www.robotshop.com/en/mecanum-wheel-set.html as long as they last.

    erco-approved, I say nab yourself a set or two. They will take some work to attach to a shaft; they are designed with a small square hole for a VEX motor shaft. Way too small IMO. Various aftermarket adapters are available.

    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • I designed and 3D printed some Mecanum wheels. They're on Thingiverse. https://www.thingiverse.com/thing:2319764

    It's a parametric design in OpenSCAD so you can change the number of rollers, roller angle, etc. if you wish. If you don't want to use OpenSCAD, the stl files I uploaded fit a Nema 17 motor are 4-inch size and have 7 rollers at 45 degrees. You can do a mirror image on your slicer to get the two 'handed' wheels you need. All you need is lots of 3d printing and some M3 cap head bolts and washers for the roller axles, and some grub screws to secure the wheels onto the motor shafts.

    c3e1d509fa76aacfc68a623bdf80cd8d_preview_featured.jpg

    I found they work okay on any floors that provide a bit of grip for the rollers - carpets, concrete, well mown lawns and similar are okay - but on polished wood, glass, slippery vinyl and such there isn't enough friction between the roller and the ground to make the roller rotate on its plain fastener bearing so the wheels then work more like regular wheels would.

    My 'robot' works okay, but I used an Arduino Due for the stepper motor control so I thought I shouldn't really post too much about it here. I've been meaning to swap over to using a Prop, but I've been too busy with other projects.
  • Nice! Can you print your rollers in Ninjaflex or some other grippy material?
    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
  • ceptimusceptimus Posts: 96
    edited January 24 Vote Up0Vote Down
    I've only ever printed in PLA or ABS up till now. I suppose something a bit more rubbery would give more grip but the rollers might need a brass or PTFE tube pressed in to form the bearings that run on the M3 bolt "roller axles".

    I thought of printing some rollers with grooves to suit O-ring "tyres" but I've not tried it - it takes a long time to print 56 half-rollers! I might just print 14 to test on just one of the four wheels.

    I could also design the rollers to take some bearings - small ball races are pretty cheap when purchased in bulk from China.

    It's my usual problem of moving on to other projects as soon as I get something roughly working - right now I'm enthused about building a solar-cell powered R/C plane.
  • ercoerco Posts: 19,188
    edited January 25 Vote Up0Vote Down
    ceptimus wrote: »
    It's my usual problem of moving on to other projects as soon as I get something roughly working - right now I'm enthused about building a solar-cell powered R/C plane.

    Same here. For once, I would love to... SQUIRREL!

    "When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

    - Pablo Picasso
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