I’ve added up the cost of the components in my new controller and it’s a lot more than I thought. It would probably be close to $300 to recreate one of these with the external joysticks. I’d hate to think of all the parts I bought that I either destroyed, never used or special cables/bits I needed for programming.
You could bring down the price by sourcing parts from eBay, and you could use the cheaper 2.4GHz XBee’s, or simplify and remove the LCD or external joysticks. Then the cost would be close to $150-200, but that does not include the hours needed to make the custom PBCs I hand made.
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.
WonderCon was last weekend, and it was my first real test of Artoo since the rebuild. I’d mentioned that both Gerard and I had problems with our batteries. We’d figured it much be the carpet, but I hadn’t had the problem at Celebration 4 – and in the back of my mine I had a niggling theory what was causing it.
For Celebration 4 I’d used 3 7Ah 12V batteries, two dedicated to powering the NPC-2212 drive motors, and one for the body electronics like the sound system, dome drive and speed controllers. But during the rebuild before WonderCon I’d decided to consolidate all 3 batteries into one block to make charging easier. I’d had issues with power before, but thought the problem was resolved and I could consolidate my battery sub-system. Runtime at WonderCon was approx. 60 minutes vs 180+ minutes at C4 – which is a huge difference.
Unfortunately, while I was redesigning my electronics and adding the charging system, I’d forgotten that the RoboteQ speed controller really likes a solid 12V supply, so last weekend as my batteries ran down and when the NPC motors first start-up they were eventually pulling the supply well below the minimum 10.5V required by the controller. It’s “intelligent” and shuts down if it thinks it doesn’t have enough power to control the MOSFET drivers. It’s only for an instant, and starts back up almost immediately as power is cut to the motors – which resulted in the very slow and slightly jerky movement.
So today to prove my theory, I reinstalled the the “dead” batteries from last week without recharging them, and added a separate 12V battery to the Power Control lines on the RoboteQ – Bingo! Worked first time. The issue was totally gone.
I’m kinda embarrassed that I went through this, because I should have remember that there’s a know “design feature” with low batteries and high current draw on this type of speed controller.
I’m now confident that I can pretty much run Artoo for multiple hours on a single charge – but I will have to reconfigure my electronics system again – making it harder to charge batteries in place.
For those of you following along from the start you’ll know that I’m using the Vex System to control my droid.
Vex was originally a joint venture between IFI Robotics and RadioShack, but they parted ways back in 2006 and IFI took full control of the Vex Labs company.
Recently Vex Labs introduced the second generation Vex system called Vexplorer. On the surface it’s a simpler (and cheaper) design, but does have some cool things in the starter kit like a 2.4 GHz remote camera. The remote transmitter is a lot smaller too, more like a game controller.
It maybe worth checking out if you’re shopping around for a programmable micro-controller to run your droid.
Looks like the micro-controller is NOT programmable. So I can’t see this being much use beyond using it as a standard RC setup. VexLabs has dubbed the new controller Vex-Blue vs Vex-Red for the original system I use.
Drive system jerkiness is all fixed. The problem was the AX3500 and not a Vex compatibility issue. The board had a dry joint on the main power control tab which was causing a short. The speed controller thought the battery was low which cause the fail safes to kick in and turn everything off to avoid damaging the Mosfetts.
I’d gone back and forth on the phone with RoboteQ for a few days, and finally they just overnighted me a new board which fixed the problem instantly. While I was removing the cables to send the old board back the tab connector popped off the board totally.
In the process of troubleshooting the problem, they also convinced me to reconfigure my batteries to have a dedicated 12V supply to the board rather than using a single shared 12V supply for everything. They explained that the symptoms I was seeing were very similar to a low battery problem due to the motors drawing too much current.
I’m probably going to keep the batteries separate for now, but will have to rethink the wiring and my fuse block as I was hoping to just get away with one battery feed which also made charging easier.
The real worrisome thing is he’s way too fast and really dangerous. He can zip around at lightning speeds and can plow through most obstacles because of his weight. I may need to have a fast/slow switch.
He’s also shacking himself to pieces and has already dropped several screws.
I received my center foot on Friday and it was the last structural part that I needed to get R2 on all 3 feet. So, my goal for Saturday was to get him running around under his own steam by the end of the day. I still needed to wire in the RoboteQ AX3500 speed controller which controls the drive system.
I added a power strip to the inside of the back mounting plate to connect all the grounds to and set about wiring things up.
I then did some basic tests of the 3500 and noticed something strange. The motor would run for a second then stop for a split second then start again, like it had a slight tremor. Message code on the 3500 status panel flickered from motor direction information to an ‘8’ – which means under or over voltage. I suspect it’s a low battery. I hope it’s not a Vex/RoboteQ incompatibility problem. I suspect I may need to add a second battery dedicated to just controlling the 3500.
I then worked on trying to get the center foot assembled and attached to the frame. But there was a problem, I was missing the pack of hardware. A quick trip to Ace fixed it, but I couldn’t get the exact parts and had to improvise on the standoffs.
Like the outer legs and feet the new foot was a snug and it took some cajoling to get the pivot point to fit.
Now that the center foot/leg was attached I was excited to think I was close to getting him mobile.
However I really shouldn’t have rushed as much as I did. What followed was a bunch of silly mistakes which cost me a lot of time. Luckily no harm was done and I learned a lot in the process.
Even in my haste to get the legs on and the motors hooked up, I’d remembered that I needed to lock the legs somehow. I’m not going to be using the satellite motors to do 2-3-2 at this points, and one of they’re jobs in the design was to lock/hold the legs in place. So I knew I needed to figure something out, but I thought it wouldn’t hurt to skip this step just for now. Boy was I wrong!
At the same time I also had the drive wheels in the back of the feet, and they weren’t always touching the floor. I’d also forgotten to reverse the drive wires on one motor.
As you can imagine his first steps were not pretty to say the least and he jerked around because of the RoboteQ battery problem, and his legs went in opposite directions. It was a total shambles. Luckily I didn’t have the camera handy for a photo.
I also needed to tension the drive belts more which meant that I had to partially disassemble the feet again. I’m beginning to realize it’s a major pain to unscrew so many bits just to fix one thing.
After stripping him back down and fixing the problems and locking his legs back in 3 legged mode I gave him another spin and here he is. He’s super fast, but I really do need to figure out the battery/undervoltage problem that makes him stop/start/jerk.
Once I get the RoboteQ speed controller working correctly this thing is going to scream.