XRP Mecanum Drive / Omnidirectional (fully printed with 2 different frames)

This is a fully 3d printed mecanum drive for your XRP perfect for indoor and small spaces. For outdoor exploration I would recommend you some of my other mods like the xrp off-road mod, the xrp track system or if you wanna go to water the xrp boat mod.

The xrp mecanum mod basically makes your XRP a 4x4, this also means you can use the XRP Big Boy chassis if you want a bigger vehicle. Anyway you will need 4 motors for a mecanum drive system! 

Also worth mentioning, this kit requires the latest chassis which is currently V1.5.3MF. This version offers a hole next to the motor shafts, so you can connect wheels outside the frame.

For older Versions you would have to modify your chassis. I do provide a XRP Axis Hole Finder For Older Frames, that will help you to drill the hole in the correct position, have a look at my models. 

Print List:

• 48x Rollers (TPU recommended)
• 4x A-Rim Parts
• 4x B-Rim Parts
• 4x Axis
• 8x Axis Safety Ring

Additional parts

You need now to decide if you want to go with the Big Boy frame or the Mecanum Frame. 

Big Boy Frame

• 1 additional XRP Frame
• 2x Big Boy Bottom Plate
• 2x Big Boy Safety Ring

Mecanum Frame

The Mecanum Frame has 2 different versions. Eventually they're pretty much the same. One requires support for printing, due to its printing position it can't have “push buttons” on the caster mount. The other version is printed in 2 parts without support but requires assembly. For this assembly I would recommend glue or a soldering iron. This version has “push buttons” above the caster mount for easier release.

• 1 part version
  • 1x Left Front System
  • 1x Right Front System
• 2 parts version
  • 1x Left Front System Caster Mount Part
  • 1x Left Front System Motor Mount
  • 1x Right Front System Caster Mount Part
  • 1x Right Front System Motor Mount

Additionally Required:

• 2x Additionally Motors ROB-24053
  • No additional controller needed, your board can handle 4 motors

Print Settings

For rotating parts that should have low friction, like axis or rollers, I recommend you to set seam position to random to decrease the friction of “bumps” that will be created by an aligned seam or try to minimize the seam.

Regarding the rollers, I would recommend TPU for better friction on surfaces and octagram spiral for evenly spread infill for better pressure distribution. But you can also just print with any of your favorite hard filaments. A random seam will reduce friction inside and give the tires a bit of profile on the outside. You can even crank that up with fuzzy skin, but don't enable it for the hole, this would dramatically increase friction and probably stop the mecanum drive from work. Also ensure you still have enough clearance between the rollers.

As mentioned above the single print part for the Mecanum drive sadly will need some support. I recommend you to disable the support tho for the in red highlighted area, because this should easily be printed by any printer without issues. In terms of speed and material usage I did use normal snug.

Everything else can be printed without support. For the rim parts I would recommend to slow down your printer when he's printing the roller axis, you want the axis to have a high quality. Also I'd recommend to use print by object for the rollers.

But you know your printer the best.

Mecanum Wheel

The 2 additional motors are absolutely required to run a mecanum drive. I can recommend you to read the wikipedia article, especially for programming your raspberry pi pico it will be necessary to understand how rotating the wheels will affect the vehicles movement. Few examples:

The blue arrows indicate the rotation of the wheel while the red arrows will indicate the movement of the vehicle. This should give you a good overview to figure out all the other possible combinations. But I also attached a more detailed table at the end of this document.

Mecanum Wheel Assembly

Leave the small indicator arrows on the rims for now. 

You always got to take 2 of the same rims, where the roller axis are facing the same direction. Start putting the rollers on one of the rims. Ensure they can easily spin. If not try to spin them around in both directions, to get rid of the friction. If that's not good enough remove the roller and check the roller axis and the roller hole for issues.

When all rollers are on one rim, hold the second rim on top of it and look thru the rim. The indicator arrow has to be either one off to the left or one off to the right. 

Then turn the upper rim against the direction the roller axis are facing. In the case of the screenshot clockwise. When a roller aligns with the roller axis from the top rim, start merging the top rim onto the rollers. All axis need to be put into the rollers before you can squeeze them together. This will not require a lot of strength once all axis are inside the rollers. Just turn the wheel and if you find an axis that's not inside the roller, gently turn it back, push the axis thru the roller and continue. After some fiddling everything should be aligned and you can gently close the rim. If everything has been aligned correctly, then the top and bottom asterisk will now be aligned as well and you can push the axis thru both rim parts. Pull and push the rims slightly apart until the axis did go thru. 

Use the safety ring to close the bottom to prevent the wheel sliding off. Ensure you're putting the safety ring on the very edge where no motor shaft mount is inside the axis.  You can now remove the indicator arrow.

There will be a bit of wiggling, but the motor axis ensures everything will stay in place and it can't move apart.

Mount the Mecanum Wheels

For the front wheels you need to install the front systems first. You can optionally use the rail connector for a bit of a more firm connection. 

If you should have gone for the XRP Big Boy Frame, just connect the 2 chassis with the bottom plates followed by the safety ring or the other way, not a lot that can go wrong.

Install the additional motors.

Then put all wheels next to the motors and look from the top down, like shown on the picture. The rollers need to point to the center of the chassis like an X. Move the tires around till everything is in the right position. Then put the axis thru the motor shaft hole and mount them on your motors. Secure the axis in place with another safety ring.

Basic Movement

This table shall just be a help for programming. I'm not claiming that this are all possible combinations. Especially with having different rotation speed on the motors there are a lot of possible combinations. 

The XRP Maintenance and Display Rig will be your best friend while you're programming and testing all the combinations.

Generic advice: If you e.g. notice that one motor spins slower than the others you can compensate that in 2 different ways. Adjusting the software e.g. letting one motor always spin a bit faster or you look at the hardware what's causing the issue. E.g. too high friction due to bad tolerances. It might be about finding a mix between both. Think of your print bed, it's working the same way. You try to have the bed as even as possible, but you still need to calibrate and fix small issues via software. With the timing being crucial for perfect movement you might also consider both approaches. But don't worry too much. Your motors already come with encoders that will support you.