"CAP" is also a long time member here and despite having MD (muscular dystrophy) is one of the most positive and helpful members on the BYT forum.

Muscular dystrophy is a group of disorders that involve muscle weakness and loss of muscle tissue that get worse over time. Recently, CAP has lost use of a hand, which can make it hard to drive an RC truck, one of his favorite things to do.

He posted on the BYT Forum about the dilemma and a few of us stated brainstorming, then ordering parts, soldering, making custom stuff and finally, came up with what we think is the ultimate one-handed RC ground transmitter. Nobody offers one to purchase (not like this anyway), nor could we even find decent info on anything like it online. We're sure we are not the first to do it, but we'll do our best to post up info on how we did it and how anyone with a similar challenge could do the same thing.

This HAS taken a long time to complete but it has traveled around the country a few times and has some pretty neat features. Yes, this is a transmitter for CAP which will enable him to operate his truck one handed (thank you Mr. Joystick). The case is custom and is made to rest on his leg (bottom of case is indented).

Here's a quick overview (in case you have the attention span of a gnat and can't make it through the whole project):

• 2.4 ghz transmitter (and receiver included...bound and ready for action)
  
• Built-in rechargeable battery pack and custom wall charger. Just plug it in, let it charge overnight and you are good to go. Kevin built the charger to output about 61ma so the chance of overcharging is nil. The batteries are 2600mah. There is an external charge port so you do to have to open the case.....just plug it in!
  
• Full 360 degree joystick controls forward/reverse/left/right.
  
• Custom, green translucent acrylic case with lower channel to rest comfortably on your leg. There should be plenty of room to put a blanket on your lap and set the transmitter on top of it to make it a really comfy setup.
  
• All switches are top mounted and easy to access/tweak (servo reverse switches, servo tuning knobs and main power on/off).
  
• Internal 12 LED lighting system is activated by a separate top-mounted push-button. Green LED's are BRIGHT and make this box look KILLER!!!!
  
• Custom BYT decals and some carbon fiber decals break up the all green case design and give it a really trick look. We left lots of room on the top carbon fiber sheet in case you CAP wanted to add some decals of his own.
  
• All connections soldered and protected with shrink wrap. Bottom of case comes off with 4 screws (be gentle with the screws in the acrylic) if you should ever need to replace the rechargeable batteries.
  

Here's the BYT forum discussion thread on it.

Kevin Van:

So for my part I received a stock controller from Chris, and promptly violated the warranty. Hobby King 2ch 2.4Ghz controller and receiver. Of course, I could hack up just about any controller to achieve the goal, but yeah, this was moderately low budget and there is no need for more in this application.

Completely disassembled it, did a little reverse engineering to figure it all out.

Hope you kept the receipt, because it doesn't matter any more! Initially measuring in circuit, as I was being lazy, found odd ball values for the throttle and steering pots. I was annoyed that I'd have to do math to calc voltage dividers so I could use normal value pots....until I looked closer...DOH! They have dividers on board....they are using normal values, glad I thought of it....all the pots in the TX are 5k, including the trims.

Decided I didn't like how inefficient the voltage regulator on it was (about 40% using a linear regulator) so ripped it out and put a switching regulator in it's place at about 97% efficiency. I used a Recom 785.0-0.5, which is a drop in switching regulator for the stock 7805 that was in the unit. It's pin compatible, about the same size, and can supply 1/2 amp.

About $6.32. Should pretty much double battery life right there. Dropping in a switcher like this is not necessarily free. You should have caps for impedance matching to the battery pack, and switching noise can trip up some circuits....luckily the on board circuit for the radio already had the caps it needed so nothing was added to address those potential issues.

It is a little fatter than stock, so I just backed it with double-sided tape to the board and used thermal standoff pins (like you'd use in power resistors, like bias resistors in a CRT) to come up to the Recom part. It's leads are such that it was intended to stand up right, not lay on it's back. Of course, you could make little wire jumpers to do the same thing.

Turns out how the board was finally mounted, I could have stood the regulator up with no ill effect. I didn't want to raise the profile of the board because none of the mounting was hammered out yet.

I did not buy new switches, the stock ones were merely located off board since they had mounting holes in them already.

I harvested a pigtail from scrap equipment (I have a very rich assortment of this kind of thing) and matching antenna to remote mount it. Now, we'll call it an ADA accommodation. Fact is, the stock antenna only mated with the molded case of the original controller and couldn't be reused. Technically you shouldn't change the antenna on a type accepted thing like this because it's rated and accepted by the FCC as a system. I'm sensitive to this, however in this case, there wasn't a viable alternative to reuse the original. However, know that the stock antenna and the replacement antenna have identical internals (the shield is stripped away and the center conductor acts as an antenna for about 3.5" ) so there is no functional difference between them other than the ability to chassis mount it because the connector is threaded.

The surface mount RF land is tiny and calls for careful soldering. There is a nearby SMT filter, that could easily be destroyed, which would be nearly impossible to ID and replace by mortals. It's too tiny and has no markings. I also tacked on a wire to a nearby GND pad and heat shrunk it to the coax pigtail to provide more support of this delicate connection.

Located and purchased a suitable joystick with appropriate pots. Wire so forward is gas, rear is brakes. Left and right are obvious, unless you have the servo polarities wrong, flip the switch. I used a 4site electronics 4SJ200-1B-M2-S joystick for about $28. They exist on ebay as well.

I simply lopped off the existing pot to pcb connectors and tacked them onto ribbon cable, and the other end to the joystick. Taking care to get all the wires in the correct positions.

Also harvested a external power supply, maybe 12v at an amp or so....added linear regulators for the appropriate voltages at about 61.5ma trickle charge. You can essentially leave it plugged in all the time and it should not ever get warm or cook the batteries. Bad news is a COMPLETELY flat pack could take 2 days to fully charge, lol. For reference, a 9v battery can supply 180ma, so it's super safe.

Shipped the whole thing off to Nick who did the box and mounting. Later he sent it to Chris, who I helped via email to pick out some LEDs and how to tap power for them. He also did interior decorating and decals, etc.

After the design was finished I decided to toss the idea of it being made out of acrylic to Mitchell Plastics & Casegoods. I use them through the company I work for, for a lot of projects. Their work is outstanding. I made an appointment with Mitch the owner of the company to go over the project. They took my drawing concept and added a few elements to it based on their prototyping (like the switch panel being removable and the holes for charging). They're the ones who get the credit for the fantastic fabrication of the case.

To my surprise when I picked up the finished piece Mitch told me that I didn't owe him anything and that he was glad to be a part of such a great project. That really says a lot about him and his company!

At that point it was boxed up and sent off to Chris!