Small XRP frame

This is a customized version of XRP chassis, part of XRP robotics kit. 
In addition to files uploaded here, you can also view and download the design from online Fusion360 hub: 
https://a360.co/43SxnfM

Differences from the original

• Smaller size (15.2cm x16cm, compared to 19x19cm for the original)
• Uses either two 18650 Li-Ion batteries or a 2s LiPo battery pack (see details below)
• Battery pack is shifted back, putting more weight on the wheels and less weight on the casters
• Same side rails and casters, so existing sensor/servo mounts can be used without modification

Bill of materials

  You will need the following:

 3d printed from this model:

• The chassis 
• Battery clip 
• Two controller supports

Parts from the original kit: 

controller board, motors, wheels, caster balls, servo/sensors

Other parts:

• Four M3x8mm button head screws
• Battery/holder (see below)

Power source

You have several options to power the robot using this chassis. 

1.  Two 18650 Li-Ion batteries and a holder. You will need to find a holder that provides barrel connector, e..g this one from AliExpress. 
2. Alternatively, you can use a 2s (7.4V) Li-Ion or LiPo battery pack. The pack should be no larger than 70x40x19mm. I recommend using a pack which contains 2 18650 batteries wrapped together,  e.g. this one from Amazon, instead of a LiPo battery pack (which contains soft pouches).
   You will need either to replace the connector (warning: replacing connector on a live battery requires great caution; any mistake can result in fire or explosion) or make an adapter from whatever connector is provided by the pack to the 5.5x2.1 mm barrel jack

Option 1 is easier and safer, but it requires you to remove the batteries every time you need to recharge them, which is annoying. Option 2 allows you to charge the batteries in place. 

Assembly

If using 18650 battery holder, snap it in place with the wires going into the opening in the front part of the robot. Snap in place the battery cover clip. Turn the robot over and attach the controller board, using the the supports and driving the screws into holes in the chassis. The battery wire should go underneath the controller as shown in the photos; make sure to route them so that they are not punctured be the pins in the bottom of the controller board. 

If using the 2s battery pack, use the zipties; you can route the wires either thorugh the front opening or through the smaller opening in the back. 

Code

Since this chassis has different wheel distance, the default code for turns and driving straight needs some changes. Work in progress, will be added here shortly.