XRP Offroad Mod

Update

With this being an early work of mine I decided to give it the TLC it deserved and improved it with everything I did learn on my journey.

The original files and instructions are available as zip archive in case you need spare parts. For everyone else I would recommend to go with v1.1.

Changes in v1.1

• Improved Safety Ring System
• Added Safety Ring Tool
• Adjusted Axis lengths
• Changed tire design
• Improved front mount

General

With this kit nothing stops you from exploring the wilds.

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

• 4x Tire of your choice (or use compatible ones)
  • The rims are for 20mm tire width and 48mm tire diameter. This is a default size, you can get fitting tires in the store.
• 2x Front Rims (shorter axis)
• 2x Rear Rims (longer axis)
• 1x Left Front Mount
• 1x Right Front Mount
• 4x Safety Rings
• 1x (optional) Safety Ring Tool
• 1x (optional) Rain Cover Hinged for external Wheels
  • 2x Rain Cover Hinges

Recommended Addons

• Any outdoor protection like my  XRP Rain Guard  or XRP Covers V2 to help deal with bad conditions
• Go bigger with the XRP Big Boy mod

Print Settings

If you decide to print tires yourself I recommend to use TPU, the infill should be rather low for the tires, but it depends on what TPU you will use and what you will aim to do with the XRP. I did go with 95A TPU, a 5% infill density and with the Octagram Spiral because it provides imo a good and even distribution for tires.

Everything can be print without support and I would recommend to print everything in the provided orientation from the files. Small overhangs like the inside of the rim might not print 100% flawless, but technical fully functional and imo less hustle than removing any support. If you want to fine tune your results you can use modifiers to slow down the printing speed for fragile areas and use variable layer height to increase details. 

The axis don't have the optimal print orientation for strength but for best quality. The strength will be sufficient for the given task, but handle them careful in between. Especially when you put the tires on the rims. The rims will work fine with an infill of 25% cross hatch. If you know you're a destructive nature, increase it to 40% and the wall count to 4. This will make it really strong. But if you handle them with care there's no need for that and it will print in about half the time. Same recommendation goes for the front mounts. 

I also like to enable ironing of all top surfaces. Also especially for parts that should have low friction like the axis, try to minimize the seam. My lately favorite solution to this is using scarf joint. Other possibilities would be to use random position so there's not “one big bump” it has to overcome or reduce the seam gap.

If you should run into any fitting issues, like the axis not fitting your XRP hole then you might look into X-Y hole compensation and X-Y contour compensation. You want the axis to be able to freely spin but also not being so lose that they misalign.

Also sometimes an elephant foot can cause slight fitting issues, but usually you don't have to worry too much about that because putting e.g. the axis thru the hole multiple times will remove the elephant foot anyway.

But you know your printer the best. :)

Instruction

Remove the default wheels and caster from your XRP. If the caster sits too tight you can use the pin of the front mounts or the xrp caster remover tool to push them down from the top.

Be careful when installing the tires on the rims, the axis are quite sensitive. Only mount the tires when the axis is not installed on your XRP, this would increase the stress and might break the axis.

Put the front wheels (shorter axis) thru the front mounts and fix it with a safety ring. It's a bit easier if you do it with the safety ring tool but you can also use pliers or your fingers. Mount the front wheels to the frame.

Put the rear wheels thru the holes and connect them to the motors. Use a safety ring to fix the axis.

The front wheel needs to spin freely, if there's too much friction it might get locked in place and will just slide, especially on smooth surfaces. If you should run into issues have a look at your X-Y hole compensation and the seam gap settings.

Disassembling

Press the “button” on top of the front mounts, with a bit of wiggling the front mount comes off easily. 

For the rear wheels you have to remove the safety rings first. Use the back side of the safety ring tool to push it off. Then just pull them out.