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$15 Walmart Mecanum Vehicle — Parallax Forums

$15 Walmart Mecanum Vehicle

ercoerco Posts: 20,181
AFAIK this is a new low price for a mecanum-wheeled vehicle. The vehicle has a 2.4 Ghz radio control syatem and a USB rechargeable battery. I didn't buy it (busy busy!) but it may be a useful chassis for someone to experiment with. Even if the chassis or motors are underpowered or unsuitable, the wheels & Lipo are worth $15 IMHO.



  • I'm very tempted. The vehicle would need a different controller in order to take advantage of the way Mecanum wheels can move. The standard controller appears to let you drive forward and back or side to side. It doesn't look like it allows motion in any direction.

    In case anyone doesn't know, Mecanum wheels allow a robot to move in any direction and rotate in place. Here's one of my old figure 8 videos.

    To really take advantage of Mecanum wheels, the control code needs a bit of trig to calculate wheel speeds. It also really helps if the motors have encoders so the speed can be controlled accurately. That's another mod I'd need to make. I'd need to add encoders to the four motors.

    A good Mecanum wheeled robot can be controlled in pretty much the same way as a helicopter or quadcopter. You don't have elevation control but the you can move in any direction and rotate just like a quadcopter using the same inputs as you'd use to control a quadcopter (minus throttle).

    At 1:52 into this video (another old video most of you have seen before), I attempt to explain how the controls on my Mecanum wheeled robot work. Starting at about the two minute mark, the video shows how fun a Mecanum wheels robot can be to drive.
  • ercoerco Posts: 20,181
    Great video, Duane! Rich (W9GFO) had a great mecanum vehicle at the Parallax Expo in 2012. He told me privately about a mecanum app he was working on with an impressive amount of feedback & mixing. I don't recall seeing him post about finishing it though. There is a lot of cool stuff yet to do with these wheels, and $15 is a small price to pay. If Duane is getting one, so must erco!
  • erco wrote: »
    Rich (W9GFO) had a great mecanum vehicle at the Parallax Expo in 2012.

    Yes, I remember seeing video of his cool robot.

    I just ordered six of the WalMart bots online. We'll use a few as Christmas presents and I'll have a few to hack.

  • Duane Degn wrote: »
    I just ordered six of the WalMart bots online. said they should arrive on Wednesday. The six bots were delivered about an hour and a half ago. About 4 hours from order to delivery. I was surprised to say the least.

    The robot charges at 5V 450mA. The vehicle has what looks like a battery compartment but the compartment is there to store the charging cable which doesn't unplug from the vehicle.

    The controller is not proportional but it does allow you to control forward and sidewards movement at the same time. There's no yaw control. The vehicle and move forward and backwards and side to side but no turning. The only turning achieved is through asymmetric friction and is not controllable.

    I'm neither disappointed nor thrilled. It's about what I expected. I suppose it's a bit better than expected since the Mecanum wheels look and feel pretty good and the motors are relatively zippy. With a new charge, the vehicle with flip on its rear when the control is changed from reverse to forward. The robot can then be reversed again to bring its front wheels back to the ground.

    It's not the most fun I've had for $15 but I consider it as a good value for the price.

  • I don't know if I should be disappointed or impressed. This thing has two motors!

    Both motors have drive shafts which extend from both ends of the motor. It's kind of crazy looking.

    I'll take some photos and upload them soon. Here's a photo of the compartment for the USB charger.


    Here's an unlisted video showing the vehicle in action.

    The battery is a 320mAh AAA Li-Ion cell. I'll include a photo of the battery when I share photos of the motors and gears.
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  • Here's a picture of the battery next to an AA cell.

    There's a sticker on the vehicle which says "The batteries inside this toy are not replaceable." It's interesting the battery has a connector even though it's not replaceable.

    The top body is held on with the four shock absorbers and one center screw.
    This portion of the vehicle is completely cosmetic.

    There's a lot of gears on each side of the vehicle to mix the motion from the two motors.
    It's an unusual drive mechanism which mixes the inputs from the two motors. As you can see, there pinions on both ends of the motors' drive shafts.
    It might be possible to convert two vehicles into a single four motor vehicle. I'd need to widen the vehicle in order for the extra motors to fit. It would probably be easier to look for some inexpensive geared motors with encoders and just use the wheels from this vehicle.

    The wheels appear to be relatively well made. There a self tapping screw holding each wheel onto the hex axle. Each wheel is held together with four self tapping screws. Another three screws hold the blue decorative hub onto the wheel. I thought I had some photos of the wheel parts but they're not in the expected folder. I'll take some photos tomorrow and share them.
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  • Duane Degn wrote: »
    I don't know if I should be disappointed or impressed. This thing has two motors!
    I've decided on disappointed. I initially thought the gearbox was doing some sort of mixing between the two motor inputs but the gears from each motor are independent from each other. It's basically one motor powers the forward wheels and one motor powers the rear wheels. If they wanted to save on materials, they could have extended the drive axles to both wheels and used half as many gears.

    There are three sets of 24 tooth gears for each wheel. These gears have a smaller 9 tooth gear in order to reduce speed. The final gear on the output has 32 teeth. One of the 24 tooth gears is only used to transmit power rather than reducing speed so the gear ratio ends up being 682.667:1.

    I get the 682.667 value from (24 * 24 * 32) / (9 * 9 * 9). (The motors have a 9 tooth pinion.)

    I can think of a few different ways of turning this into an omnidirectional robot.

    1. Cut the drive section down the middle and add two additional motors. This would result in a wider vehicle.
    2. Cut the one set/side of gears off of two vehicles and combine the vehicles into a wider four motor vehicle.
    3. Use the wheels with a set of appropriate gear motors and abandon the original motors and gears.

    I'll likely give option 1 a try first. I believe I have a few sets of appropriately sized motors in my stash. I'll pull the pinions off of one side of the original motors and use them on the added motors.

    If I give option 2 a try, I'll likely also try option 3 since option 2 will leave me with an extra set of wheels.

    Speaking of wheels, here's a photo of one of the wheels taken apart next of an assembled wheel.


    I was pleasantly surprised how easy it was to reassemble the wheel. These sorts of wheels can be a trick to assemble and require a jig to hold the rollers in place as the side supports are added. I was able to pop the rollers in one by one on these wheels without much trouble.
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  • Thanks for the detailed tear down!
  • Publison wrote: »
    Thanks for the detailed tear down!

    I told my wife I was putting photos of the parts up on the forum so other people wouldn't have to take apart their toy. My wife looked at me and said "You'd still take apart yours even if someone else had posted photos." She's right but hopefully not everyone has the take it apart illness as bad as me.
  • Nope, nope, Duane!

    I believe there is a way better illness going on there, on top of your workbench...

    You know, not everyone would take it apart, document, and comment, better than you do, which I have to agree, indeed! :LOL:
  • Duane Degn wrote: »
    .... hopefully not everyone has the take it apart illness as bad as me.
    I have it bad too! Unfortunately, I’m void of the put-it-back-together gene!

    Thanks for sharing!


  • Neat! Thanks for the teardown.
  • Duane DegnDuane Degn Posts: 10,565
    edited 2021-01-18 02:33
    I have a couple motors which should be the right size to fit the mechanism and pinion gear. My plan is to cut the frame and add a spacer between the two sides in order to fit the additional motors. Here are a few photos which hopefully convey my plan.

    Here's the top of mechanism.


    The photo below shows one of the old motors and one of the new motors inside the uncut frame.


    The motors have been removed in the photo below. I'm hoping to preserve enough of the motor alignment features on each half to support both the old and the new motors.


    Here's a photo from the bottom of the chassis.


    I purchased the two additional motors from Pololu years ago. Apparently these motors are supposed to be better than the ones which came some robot set I had previously purchased. If the new motors are noticeably different than the original, I'll likely purchase a couple more new ones so all four motors are the same type.

    I'll hold off cutting the plastic in case any of you have a better idea on how to add two additional motors to this vehicle.

    I debated cutting the unused drive shaft from the old motors but I'm afraid cutting the shaft could damage the motor.
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  • ercoerco Posts: 20,181
    edited 2021-01-18 03:13
    Fantastic report, Boss! Weird that there's no yaw but I'll get one! They are in stock at my local store.

    After swapping controllers & moddinf for 4 motors, it would make a neat FPV vehicle for scooting through the house.
  • erco wrote: »
    I'll get one!

    Don't feel obligated to do so. It would be fun to see how you convert one to four motor drive but as long as I'm modding one of them, I could mod a second one for you (serious offer).

    I figure an easy controller would be to use a HC-05 module to receive commands from an app like Joystick Bluetooth Command. It's not ideal for a Mecanum robot but I figure a few of the buttons could be used as yaw control or to switch modes so the joystick would also control yaw.

    I've tried my hand at making my own sort of robot controller but I don't think I ever got my apps to work as smoothly as Joystick Bluetooth Command.

    The controller which comes with the $15 vehicle has four buttons inside. I'll add upload some photos of the inside tomorrow.

  • Duane Degn wrote: »
    ...but hopefully not everyone has the take it apart illness as bad as me.
    I've had that illness since I was old enough to figure out how to open things...not always with the proper tools.
    That said, the best way to figure out how something mechanical works is to take it apart and (hopefully) put it back together with a minimum of leftover parts.

    I'm one of those that disassembles broken appliances and tools to get the screws and other fasteners. Sometimes they come in handy... but boy do I have a lot of bolts, screws, nuts, etc. Part of my downsizing will be to sort this junk out and donate it to someone else's garage.

  • I realized most of the photos I've uploaded have been of the gearbox, motors and wheels. I'm including some photos of the outer body below.

    The parts labeled "B" and "C" are parts I haven't previously documented. The same type of screw used at the top of the shocks are used to secure the shocks to part B. There's a fifth screw which passes from the inside of part B up into the center of part A. This lets the top chassis rock semi independently from part B. The screw that holds these two parts together has a 10mm diameter head to keep it from passing through the 7.5mm hole in the top of part B.

    The photo below shows the drive portion inside the open outer shell. The gears and the gearbox covers have been removed from the drive portion but hopeful you can make out how the drive portion fits inside parts B and C. Here's another photo with part E removed from part C. Part D is not in the photo.

    The above photo also shows the position of the PBC and the battery. Here are a couple more photos of the one sided PCB.
    The USB charging cable was cut from the bottom right corner of the PCB. A red wire was connected to the location marked with "++" and the blue wire was connected at the location marked "---". The red LED lights while the battery is charging.

    The remote control is pretty boring but I did take it apart and took some photos of the inside. I'll post these photos in a new reply.

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  • Before I move on to the remote, I found a few more photos I probably should have included earlier. The one below gives a pretty good idea of the parts of this vehicle. The gears, PCB and screws are missing but You can see the main parts reasonably well. I'll use the same letter labels as before.

    Below is the pile of gears and metal shafts. Gears210119a.jpg

    The two rear large shafts are permanently attached to part E. The two front shafts are included in the pile shown above. Most of the shafts are the same size but there are two shorter shafts. Both sorter shafts are used in one gearbox. I haven't tried to put the gears back in a gearbox yet but I don't think it's going to much harder than putting a servo gearbox back together. Having all the gears the same size should make it easier.
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  • Here the inside of the remote.

    The remote has four buttons internally to control the vehicle. The trigger can press the F and B buttons and steering wheel can press the L and R buttons.

    I've circled the bits of plastic responsible for pressing the buttons in the photo below.

    There isn't a power switch on the remote. The buttons must also cause the device to turn on. Here's the other side of the PCB with the transmit circuit.

    The remote is powered by two AA cells which are included in the package.
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  • I cut the drive section in preparation to add additional motors.

    I think I have found a flaw in my plan. Apparently these types of motors can have very different power levels. One thought was to use four of the Pololu motors so the power levels would all be similar but I realized one side of the drive section expects the back plastic section of the motor to connect with it. The motors from Pololu only have shafts extending from the metal end.

    It should be possible to balance the power levels in software with appropriate PID tunes for each motor type but it should be nice to start out with identical motors. I'll need to think on this a bit. If any of you have suggestions, I hope you chime in.
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  • Duane Degn wrote: »
    one side of the drive section expects the back plastic section of the motor to connect with it.

    I found these on Aliexpress.


    They have the dual drive shafts so they should work on both sides of the vehicle. They're less than a dollar each if enough are purchased to spread out the shipping.

    I found some motors which look like they're better quality but they're more than twice as expensive.


    The cheap ones will hopefully arrive in March. I'll try to have the h-bridge and encoder circuits figured out before they arrive.

    I haven't decided where to add the encoders. It would probably be easiest to add an encoder to the unused shaft but if I cut these off, I could reduce the width of the vehicle. In other "upgraded" vehicles, I've added an encoder disk to one of the gears. This shouldn't be too hard and it would allow for a narrower final robot.

    Leaving the extended shafts in the center of the robot would widen the robot by about half an inch (13mm). It's the difference between a robot 1.5" wider or 2" wider.

    The vehicle is 5.5" wide to start. The final width will be either 7" or 7.5" depending of whether I leave the center shafts or not. I might just split the difference and cut the shafts barely long enough to secure an encoder disk to it.

    I need to go through my encoder and h-bridge stash to see if I need to order any more parts.
  • I have a some QRE1113gr sensors in my collection of electronic parts. I laid out a PCB to use eight of these sensors as four quadrature encoders.

    Here's the side which will monitor the left motors.

    And the right side:

    The hole is for the rear motors' axles. The 0.1" headers will protrude behind the motors. I didn't add any mounting holes since the PCB will be sandwiched between the motors and I'd have to extend the dimensions of the PCB in order to add the mounting holes. I didn't want to increase the dimensions of the PCB since it would make the PCB more expensive (OSH Park charges by the square inch). I might end up needing mounting holes but I'm hoping I can 3D print some sort of bracket to hold the PCB in place if hot glue doesn't do the trick.

    As I mentioned, the headers extend into the rear area of the vehicle. Here's the PCB with some lines indicting the top of the gearboxes. There are also circles to indicate the size of the motors. Hopefully this will give you a better idea of where the encoders will be positioned.

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  • Are you still watching this thread erco?

    If so, I'm hoping from some input about battery and chargers. The included AAA Li-Ion and charger seem pretty small for a four motor robot. I'm trying to figure out a practical and relatively inexpensive alternative.

    A while back I purchased a few of these 16450 holders/chargers/regulators. (I think someone on the forum suggested them. Was it you erco?)

    Besides the Li-Ion charger, these have 5.0V and 3.3V outputs. While they aren't as inexpensive as other options they make life easier by including these regulators. I'll likely power the motors with 5V and use the 3.3V to power the Propeller and encoders.

    One of the big downsides to using these is the size. I don't think they will fit in the internal battery area. They'll likely need to be mounted on top of the gearboxes.

    Any alternatives I should consider?

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  • ercoerco Posts: 20,181

    Just seeing this now, Duane. Been busy at work!

    You've done some marvelous sleuthing here, Boss! I got one from my local store and checked it out. The only way to turn/yaw is to get it up on 2 wheels and do a fast spin. Too fast for fine control, but better than nothing! There's a lot there for $15 even if it only allows a portion of the mecanum's potential. IMO, kids will like this, and it might actually be better for young kids (my first RC) since it eliminates that perceived control reversal when the vehicle turns and is driving toward them. That throws a lot of kids (and adults) off.

  • Eh, Duane, the vendor says they are the classic 18650 size battery holder boards.

    Incidentally @erco thank you for the snow and sleet and wind. It's making a difference here to see how the City performs this season, not bad, NJ, poor, and the rest of NY State, okay.


    Mascot outside racing the snow.

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