This PVC structure is designed to prevent the RMP from falling more than (approx.) 45 degrees forwards or backwards.  There are wheels on each of the four pipe ends.  Unfortunately, this structure is not sufficient because the RMP balancing control system will become unstable if extra points of contact are made with the ground.  That is, if the RMP tips and lands on the safety wheels while in balancing mode, it will "freak out."  To overcome this instability, a special electronic kill system was devised such that the RMP will shut off if any of the wheels make contact with an object.  In this kill system, a switch is attached to each of the four wheels, all of which are connected in a series circuit located inside the black metal casing attached to the steering column of the RMP.  The ends of the circuit are attached in series to one of the existing two kill-switch connectors of the RMP as seen in the diagram below.  

female end of the kill-switch connector                                                            male end of the kill-switch connector
connected to brown kill-switch wire                                                               connected to purple kill-switch wire

The circuit is shown in the images below.  The yellow wires are coming from the wheel switches.  One of the connections from the existing kill system of the RMP was bypassed, in our case a brown and purple wire connection pair, the connectors of which were plugged into our circuit board.  

                                 

 

Wires from the normally-closed switches attached to the wheels are run through the PVC sturcture and out drilled hole as seen below.

   

Each switch is embedded in a hollowed out wooden dowel held in place inside the PVC pipe.  The wires out of the switch are fed through the dowel and up the PVC pipe.  The wheel is attached to another wooden dowel which has a slot that is allowed to slide up and down over a bolt placed in the PVC.  The following diagram shows the resulting arrangement. Note that there should be enough room when the holes are drilled so that the wires from the switch can easily get around the bolt.

 

Thus, when a wheel is pressed, the dowel it is attached to will slide up the pipe and press the switch, opening a connection in the series circuit and causing the RMP to shut off.


It should be noted that when the RMP does fall onto our safety mechanism, the switches are usually destroyed from the weight and have to be replaced.