SO, HOW'S IT DONE?
There are many ways.
I wanted a simple box that allowed me to plug straight into all of my five powerchairs. The easiest way to do this wasn't the cheapest. I used a thing called the OMNI PLUS. Because all of my 5 chairs use the same Penny and Giles (Now PG Drives) control systems. Namely the popular PILOT PLUS system with an oval joystick pod.
So I acquired the device called an OMNI PLUS (now superseded by the R-NET version of the same thing). That looks like this:
It's intended use is to integrate "speciality controls". It has a D connector on the end where that grey plug is plugged in above.
It allows an ANALOG VOLTAGE to be injected here, a DC input to control the powerchair. There are similar devices available for almost all of the high end rehab type powerchairs. They allow external joysticks, or other switches etc to all be interfaced with the existing wheelchairs control system.
I used this analog input, to allow me to build a simple interface that connects a RC model plane receiver to the OMNI to control the chair. To send a simple DC voltage signal. One for LEFT/RIGHT and one for BACK/FORWARDS. It lives inside this black plastic box that the OMNI device is mounted on top of.
It looks complicated. Its not. But its out dated and we have a better much simpler way now! So I wont go into the how's and whys here.
HISTORICAL DATA FOR INTEREST
Just a quick generic description for those interested. Inside that black box is an old style PCM (pulse code modulation) 35mhz RC receiver. (Same as the US 72mhz type radio control systems from a few years ago). Its SERVO output signals go to two tiny "forwards only" model flight speed controllers. These go from 0v to 12v to drive brushed electric motors. In fact its a pulse width signal. But its good enough to approximate a DC output. So MID STICK is 6v. (So we get 0v low stick, 6v central stick. 12v high stick.) Same on steer channel.
A bunch of passive resistors and adjustable 20 turn resistors take the speed controller signals, and turn them into the +/-1.2v "voltage swing" above and below the 6 volt reference point on the omni device, to simulate the JOYSTICK that the OMNI device was expecting to be connected to. Houston, we have control!
Then just plug the wheelchairs "pods" normal connecting cable into the Omni plus instead and we are ready to drive any PG Drives powerchair remotely...
The RADIO CONTROL system you use MUST be encoded. It MUST FEATURE A FAILSAFE SYSTEM. Or you will end up with a powerchair driving across a motorway with you watching in horror! Or worse... Be sure you fully understand the details!
So then, just some simple components and passive resistors, a voltage regulator chip, and a few capacitors for stability. That's all it took. And a lot of careful fiddling and setting up. Worked reliably and faultlessly for about 10 years. Then a fiend on my forum called woodygb built me a better setup! This page used to explain how to do all of this stuff. But that was in the past. Now, there's no need! He will sell you a plug and play interface that's ready to go. See bottom of page.
ITS 2014, THINGS HAVE MOVED ON!
There are now better and easier ways!
A member of my Forum designed a simple Arduino one chip computer device that goes between any modern encoded model aircraft type transmitter/receiver system and the same OMNI type input device. He will sell you one of these plug and play interfaces that's ready to go. See bottom of the page.
Remember that these Omni or speciality control input thingies are also available for any powerchair used for rehab duties. So check out yours or ask on the forum Forum if you are stuck!
This is basically now a plug and play module. However to allow RADIO CONTROL of your powerchair it also requires:
Personally I use this excellent JR 12X 2.4ghz DSMX power boosted transmitter. You don't need this expense of course. I do for other reasons. But its nice!
Any cheap modern 2.4 ghz or 35/72 mhz ENCODED or PCM type RC system will work fine. As long as it has a suitable fail safe system. That means it can drive all its channels to a pre determined position on signal loss. Or REMOVE all signals totally on loss of connection.
As of 2014 the black box the OMNI device sits on now just contains the PLUG AND PLAY INTERFACE designed and programmed by my forum member woodygb, and a Spektrum AR10000 receiver. (And additionally three external satellites receivers for improved signal security as can be seen in these photos).