We've got the physical ArduPilot boards now, and the above is one with the components mounted. As you can see, it's pretty small! We've got channels 3 and 4 (throttle and rudder--that's the ESC and servo in the pic) from the RC receiver (at left) going through the autopilot. It can handle two more channels, but we're not using them right now. When the autopilot is in control, it will steer with the rudder and maintain altitude with the throttle. Elevator and ailerons are under the control of the FMA CoPilot for stabilization.

Channel 5 is used to turn the autopilot on and off and goes into the on-board hardware multiplexer/failsafe that Jordi designed and we've incorporated into this board. Finally, that's the GPS (EM406) in the top left corner.

This board is just for testing, and I can already see a few small tweaks to make in the next board (we'll switch to a different GPS connector, for instance). I'm still working on the code, meanwhile, but I can already tell you that it will be much simpler (and better) than the Basic Stamp code, thanks the superior hardware of the Arduino. Speaking of which, this project got a nice call-out from the official Arduino blog!

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Comment by James Ross on June 1, 2008 at 9:51pm
It looks like a few components are missing including the ATTiny85. I was thinking...couldn't you simplify the board by getting rid of that and using the Arduino for MUX switch control? It'd be a bit less flexible since manual control would have to be the default, however.

If you're changing the GPS connection, a fourth Tx pin would be a nice addition for a potential GPS upgrade.

I'd be interested in building, writing/sharing code, and flight testing one of these.

3D Robotics
Comment by Chris Anderson on June 1, 2008 at 9:57pm
Yes, I'm waiting for the ATTiny and two resistors, which should arrive this week. Then I can start testing code on the real board, rather than the breadboard it's currently on.

Of course it would be easy to do the MUX in software, as we originally did on the Basic Stamp autopilot. But that defeats the purpose of a failsafe, which is to be based on a different hardware circuit that won't crash, even if the autopilot software does.

Good point on the GPS pins. I wish there were a standard GPS connector, but there isn't. For now we'll be using this one, which does have extra pins.

Once we've got some working code, I'd be happy to make you a board for testing.
Comment by James Ross on June 1, 2008 at 10:46pm
If I'm understanding the Basic Stamp autopilot correctly, you used the Stamp to reproduce the PWM signals from the receiver before going to the servos. In that case, the stamp could fail and then you'd lose autopilot control and manual control. Obvious problem there.

All the ATTiny does is send a HIGH or LOW to the Select A/B pin on the 74LS157D. I was suggesting that this could be done by the Arduino instead. If the autopilot is functioning, it can send HIGH to the Select A/B pin on the 74LS157D. If the autopilot fails, it would go to low.

I was only thinking about hardware failure. I suppose the autopilot software could get caught in an infinite loop and never allow you to switch. Ugh. It's late here.

3D Robotics
Comment by Chris Anderson on June 1, 2008 at 11:02pm
Yes, you rightly caught the error in your idea ;-)

It's software failure (I.e. the Arduino locks up) that we're worried about. That's why we do the MUX and failsafe on entirely different silicon.
Comment by Wyliest on June 1, 2008 at 11:12pm
Is there any way to program this board to control more than 4 things at a time?

3D Robotics
Comment by Chris Anderson on June 1, 2008 at 11:19pm
Absolutely. We've broken out all the Arduino's I/O pins into jumpers. We only mulitplex four channels (meaning we only switch between four channels in from the RC or from the Arduino) but you can add at least eight more servos or switches that originate from the Arduino (and the autopilot program) itself.
Comment by Scott James on June 2, 2008 at 3:58am
This is looking really good Chris!
Comment by Wyliest on June 2, 2008 at 1:06pm
Where is a good place to buy components? Things like X1 and S1.
Comment by James Ross on June 2, 2008 at 1:27pm
They come in the BoArduino Kit. If you don't want to buy that kit, probably digi-key or mouser.

3D Robotics
Comment by Chris Anderson on June 2, 2008 at 1:42pm
Once we get the final board tested, I'll post a list of every part and exactly where to get it. But the short form is that all you need is:
--Boarduino kit
--Multiplexer and ATTiny chip
--Two 220 5v resistors and One 4.7k 5v resistor


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