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Customized XRP robot

My customizations of XRP robot from Experiential Robotics

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My customizations of XRP robot from Experiential Robotics

Preliminaries: what is  XRP?

XRP is a robotics kit created by consortium of several organizations, including Sparkfun, Worcester Polytechnic Institute, FIRST, and many more; see https://experientialrobotics.org/. It is primarily intended for use in education. 

It has been in beta for about 2 years, but recently (March 2025) they released version 1, which has significant improvements.

Useful links:

Features

XRP is a typical 2-motor small differential drive robot, programmable in micropython. In addition to basic features, it also has:

  • Motor encoders
  • IMU and code to use it for turns
  • support (connectors and code) for additional motors and servos

Main feature of XPR is that it is easily customizable (unlike, say, Zumo, 3pi+, or Alvik). Chassis is 3d printed (and it has been designed with great care), making it easy to modify; there are numerous attachment points for adding extra actuators or sensors.  

It also comes with a well-supported library and a whole course curriculum, and the price is reasonable - if you are willing to 3d print your own parts, the rest is just $99, and they offer discount to educators/robotics teams, which brings it down to $73. 

Weaknesses

Here are some things I think can be improved. Most of them are inevitable consequence of designing the robot to be cheap and used in schools; some are my own preferences - to each, his own. 

  • Size. The XRP is slightly too large (19x19 cm) for my taste; I'd prefer it to be slightly smaller.  
  • Battery. The kit uses 4 NiMH batteries, which provides about 5v fully charged - barely enough for motors. It'd be better to use LiPo (though I understand the safety risks, especially when used in school environment) or 5 batteries
  • Tiny switch and buttons. The main power switch is small, and I really like the on/off be large and sturdy, so you do not have to squint looking for it when your robot is misbehaving
  • O-rings as tires: sometimes they do not provide enough traction
  • Sensors: 2-sensor line follower and a HC-SR04 distance sensor work as a starting point for beginners, but the robot would really
  • User interface: XRP has one NeoPixel and one user button. It works, but I'd love to see a proper OLED display and several user buttons, like 3pi+. 

Since the whole design is open source, I am trying to modify the XRP to address all of the above.  I'll document the project  here.

My modifications

Better wheels

I made new wheels which work with Pololu's silicone tires https://www.pololu.com/product/3409

They have same diameter as original wheels, so they can be used without any modifications to the rest of the chassis.
Design files are here: https://www.printables.com/model/1275321-wheel-for-xrp-robot-pololu-tires

Display board

This add-on board contains a 135x240 TFT SPI display, 2 user buttons, a large on/off switch, and two neopixels. It plugs into the headers of the XRP controller. 

Source files are in github, and full documentation at https://xrpdisplay.readthedocs.io/

Custom chassis

My final modification is creating a custom chassis for the robot. This is work in progress.

Features:

  • Smaller size
  • Uses two 18650 batteries

Design in Fusion 360: https://a360.co/43SxnfM...

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