I posted this photo a few days ago for people to try and guess what I was working on. Alas, nobody got it right.

Short answer: It’s a Dual Receiver Board.

We’ve had issues at some events where our 2.4GHz Spread Spectrum radios cause problems like interfering with WiFi setups, and we’ve been asked to limit where who go. Luckily, on my Futaba 10C I can quickly switch out it’s transmitter module to either be 2.4GHz FASST or old school 72MHz FM. So I devised this little board to allow me to have two receivers (FM and FASST) connect to Artoo at once, and flip between them with a flick of a switch.

I’ve had this idea for a while, but only now getting around to implementing it because Maker Faire is in a few weeks, and I know we’re going to have interference problems and I didn’t want to limit myself to either FM or 2.4GHz – or have to make a fiddly change in the field.

Receivers connect on the left and the real servos and speed controllers connect on the right along with receiver power. Ignore the black/red/white wire color on the cables coming out of the receivers. I’m only connecting to the signal out on pin 1 for each channel, and the only nice wire I had handy was standard servo cable. The last pair in the row adds power/ground and are tied to the select switch.

I’m also tinkering with some other droid controllers and this will allow me to have them connect without disrupting too many things, but more on that later.

I think I’m almost done with my new keycoder, it’s gone thru several iterations and I’ve ironed out most of the bugs.

I’d posted earlier this week that I’d started with a box I made out of aluminum angle, and added a bunch of momentary toggle switches, I then took the guts out of two RF remotes and wired them up inside. Sounds easy but it didn’t feel like it at the time.

The switches are mini (on)-off-(on) momentary, I really wanted to try and get sub-mini’s that just did (on)-off, but I couldn’t find any at a price I was willing to pay. I think the switches I ended up with worked out to be around a $1 each after shipping.

Space is very tight and I really didn’t want to make the box any bigger than absolutely necessary, so I ended up trimming the RF boards down and consolidating the antennas as well as removing the two batteries.

The switches center solder tabs are common and wired together

This is the spaghetti I’d created once I was “done” wiring the switches in

With being generous with the wire I’d forgotten it all had to fit in the box somehow! So I ended up shortening everything down. I also wrapped the backs of the switches and any critical parts of the boards in electrical tape.

I’d tried really hard to fit rechargeable batteries inside too, but ended up with a better solution I think. I ran a cable out and up into the battery compartment of the Futaba to share it’s battery. The cable has a Y split in it for easy removal. The RF remotes come with a 12V battery, but I’ve tested and found that they work very happily on the 10VDC coming from the Futaba. When I double checked my older remotes their batteries had dropped to 6V and were still working fine.

So, that’s my new CTEC keycoder almost done.

Lessons:

• Having the antenna internally limits range so I’ll be moving it outside.
• Total cost was roughly $94 (incl. two RF setups $60, aluminum $10, switches $24), and about 2 or 3 days of work. On the other hand the Vantec Hitchiker product is around $450 – and only works with their special Futaba 75Mhz FM 9CAP, but does have some great features that I will need a cheap micro-controller to replicate.
• My keycoder weights in at 10oz, adding to the already heavy Futaba setup at almost 2.5lb. So I may look into making a plastic box – but the weight of the switches definitely adds up.

One last trick I learned is that you can have multiple remotes control a single RF receiver. Yep, you heard that right. I’ve been controlling multiple RF receivers with one remote for a while, but had no idea it would work the other way around – each remote doesn’t not need to have the same code even. I accidentally found this out while trying to mate the new keycoders remotes to my droid and found that my older remotes still worked.

Related:

• Mystery Box
• Mounting RF Remotes to the Futaba
• Sound System Demo Video
• Sound System Work
• 12 Channel RF Remote Notes
• What the Beep!

I had to find a better way to mount the RF remotes to my new Futaba transmitter. I’d originally had them mounted to the sides of Vex transmitter, but really didn’t want to go this route this time around.

I’m still toying with the idea of taking the electronics from the two RF remotes and installing it all in a custom box that would look similar to the Vantec HitchHiker /keycoder, but it’s been almost a year since I blogged something similar, and I’ve yet to do it 🙂

After some experimentation, I went with a very simple acrylic bracket to fix the main RF remote on the front of the Futaba, making it very easy to control with either hand. It does cover the screen, but to be honest it’s rarely used and the bracket is easily removed or lifted.

The bracket is only secured in one spot, the bottom of the Futaba with Velcro for easy removal.

I mounted the second RF remote sideways on the battery compartment on the back of the Futaba. Right now it only has functions that aren’t used often, so I don’t think it’ll be to inconvenient having it there.

The only real catch with this setup is the antennas, occasionally I’ve found it necessary to extend them if I get to far away from Artoo.

Spent the last few days playing with the new Futaba 10C transmitter.

I had to re-calibrate the joysticks with the RoboteQ AX3500, and took the opportunity to review my speed controller setup, and tweak some of the parameters. After I was done looked like something like this –

Control Input: RC
Motor Control Mode: A and B Mixed
Input Adjustment: Logarithmic Strong
Amps Limit: 60
Acceleration: 682 (milliseconds)

I changed the Input Adjustment to Logarithmic (from Exponential) and decreased the Acceleration Delay to 682 ms. This controls how fast Artoo reaches his maximum speed and time to stop. I found that anything lower made him too jerky as he tries to stop on a dime. Both these parameters will make Artoo a little bit more responsive.

On the Futaba I increased the end points on each of the servo channels to 140%, but I suspect I could have left them at 100% due to the joystick calibration on the RoboteQ.

I also had had to reverse the direction on some of the channels.

I’ve managed to get the signal Fail Safe to work on the Futaba. Many of the older Futaba can’t do this, or at least not on all channels. For example, I know the 7 ch 2.4Ghz receiver can only do it on channel 3/Throttle. Which makes sense for airplanes, but not very good for robotic applications.

The default setting on the 10C is “Nor” which will set the receiver to continue to send the last good signal received out to the servo, or in my case the speed controller. This would cause the droid not to stop if I ever lost power on the transmitter or it’s link to the receiver in the droid.

Hoping that I’ll never need to use it, but at least it’s setup now.

As a side note, I’d almost went with an RC setup from Spektrum which offer a separate receiver (BR6000) specifically design for robotics, but it’s only 6 channels and I’m not crazy about the Spektrum transmitter setup, and really liked the extra knobs and sliders on the Futaba 10C.

I’ve also discovered that the extra FM antenna on the 10C is easily removed, and has zero effect in the transmitters operation. I was suprised to even see it installed when I got the unit. I’ll need to make a plug to fill the hole.

My Futaba 10C arrived yesterday. It’s a 10 channel 2.4Ghz FASST spread spectrum capable receiver and a big step up from the Vex transmitter I’ve been using.

It’s the newest receiver from Futaba and positioned right in the middle of their higher-end line up and very competitively priced. I’ve had it on back order at Tower Hobbies since late February and the price was around $580 after a coupon and shipping and handling. Compare this to almost $1,300 for the 12 channel Futaba or $2,200 for the 14 Channel, I think they have a winner on their hands – plus both of which are 72Mhz out of the box and will costs several hundred dollars to go to 2.4Ghz.

A couple of reasons for my upgrade

• I’m tired of having channel conflicts at events and the 2.4Ghz system will fix this problem. For most builders it’s probably not an issue as you’re probably the only bot at an event, but I seem to be at a lot of events where there maybe dozens of RC devices being used, and often run into trouble.
• The Vex transmitter was pretty bulky and hard to hold – it’s done me well and I’ll need to couple the Futaba with a micro-controller for some functionality I had planned for the Vex micro-controller.
• The 2.4Ghz antenna is much shorter and the range is supposed to be better, especially indoors.
• I’ve experience a slight delay/lag when routing the control signals thru the Vex microprocessor – there was no real way around this with the old setup.

The 10C is comparable to the older Futaba 9C that many builders use, but it’s 2.4Ghz spread spectrum out of the box rather than 72Mhz, and it has the extra channel. However the case is all plastic and I’ve already managed to ding it. I suspect the 9CAP will be discontinued at some point as it has issues with upgrading to a full 9-ch 2.4Ghz system. I almost bought the cheaper Futaba 7C ($280 at Tower Hobbies), but the 10C had some extra featured I really liked, in particular there’s a lot more switches, knobs, sliders and dials to use on opening doors and lifting things.

It more of a pro unit and can also switch between 2.4Ghz spread spectrum and regular 72/75Mhz bands using standard Futaba modules, whereas the 7C can only be 2.4Ghz.

The 10C weights in at 2lb 4oz, about the same as my Vex transmitter, which surprised me. The 10C feels much lighter in my hand, but it’s probably because it’s less bulky.

It came with a tiny R6014FS 14-ch receiver, but only 10 of the channels can be used with the 10C. It’s also compatible with with some of the 7-ch Futaba FASST receivers.

A word of warning on the new Futaba receivers. Whereas many previous receivers offered a signal output of 3.0 Volts, the latest generation of ICs has been designed to operate at the lower voltage of 2.7 Volts in order to increase their operational speeds.

My initial tests with the RoboteQ and Dimension Engineering speed controllers was successful, but your mileage may vary and worth checking with the manufacturer before making a purchase.

The plan right now is to replace the entire Vex microprocessor sub-system with either PIC, PICAXE or Arduino micro-controller. I’ll probably directly connect the Futaba receiver to RoboteQ drive system speed controller, and eventually route all the other channels thru the micro-controller to help automate some of the functions.