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Permalink Reply by Andre S on August 1, 2012 at 3:35am

Hi,

I have an APM1, Arduino Mega and 2 Uno's. Mostly used the Uno's for learning Arduino stuff that I wouldn't want to try out on my APM. IMHO, the main limitation of the Uno is that it has only a single serial port. For example, GPS and telemetry each normally consume a serial port. There is this thing called software serial but I never got either one working with GPS or Xbee telemetry with the Uno. Maybe I didn't try hard enough or maybe also the reason is the optimized interrupt driven Serial library that APM uses.

So in short: if you want to go the hard way, sure it is possible. As you say, you'll at least need an IMU and GPS. If you want to do antenna tracking for FPV then some kind telemetry will be useful. If you want to go the (comparably) easy way, buy an APM (either APM1 with separate IMU board or APM2 or 2.5 with integrated) and use the Uno for something else. I'm actually just using one to test my antenna tracker. First, I record GPS coordinates to EEPROM, then I connect the xbee and simulate position updates.

Cheers, have fun,

Andre

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Permalink Reply by Etienne on August 1, 2012 at 4:00am

Thanks for the quick response.

I'm loathe to use expensive hardware whilst I'm still in the "getting my feet wet" stage.  

So if I understand correctly, I can use the UNO board to get a feel for the technology and get basic AP and stabilization going (using an IMU and AP that I can transfer to a Mega board later).  Then once I'm comfortable I can spend more on a "proper" solution and just transfer my IMU and GPS to the Mega board for full AP and telemetry?

What would be the best IMU and GPS that would work with an UNO and then can be transfered later to a Mega-type board?

My first goal would really be within visual range Autopilot and stabilization, with hardware override should the AP fail (using HK's on board buddybox system).

I see I can get the Arduno Mega easily locally too.  Is that a good enough board for a full AP setup?  Or MUST it be the APM1 or 2?  I prefer to try to source stuff locally as it removes the shipping delays and costs for me.

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Permalink Reply by Vernon Barry on August 1, 2012 at 4:44am

My first goal would really be within visual range Autopilot and stabilization, with hardware override should the AP fail (using HK's on board buddybox system).

If you are building a multi-rotor, forget this idea all together. You (a human) cannot fly a quad from RC alone without the active stabilization. So if your APM fails, you crash no matter what.

Get this idea out of you head that you can do it on cheap hardware and thus "save money" because what happens is you crash or the cheap hardware doesn't work, you get frustrated and now spend more money than just buying a kit and do it once because the kit will fly correctly the first time.

On a plane, the scenario is a little different because a plane can fly with RC control only, and then you can add only the ardupilot "features" you can afford. The APM doesn't work anywhere near as hard in a plane, but in a heli, it is constantly working just to stay in the air. So for an airplane, maybe but be prepared to do some heavy work with adapting code and further, maybe you still crash.

Next,

cannot figure out whether I can get the same sort of setup using the Uno board

The answer here is that no, the current code won't fit, it doesn't have enough IO, memory, or flash. Follow that with an good IMU stick is between $80-100 and you still need a $40-$80 GPS on top of your $30 UNO and then you were even talking about  failsafe for  $??? Oh, and I forgot, you still need a PPM encoder (another 328P) so 2 Unos at $30 each. I count at least $200 or more in hardware to poorly mimic the APM.

An APM is only $200 and has all those, works with the code out of the box, and has a barometer.

The math doesn't add up and neither does the logic. It will cost you more money, time and frustration in the end. If your goal is to learn and expense and time are no issue, go for it. But is like the saying, "You can have it Fast, Cheap, or Reliable, please pick one".

 

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Permalink Reply by Etienne on August 6, 2012 at 5:37am

No this will be for a plane (and a fairly stable one at that).  My idea was to start with just stabilization.  That way I can look around with the FPV camera without spending too many brain cycles on keeping the plane going in one direction.  I can also use a stabilized plane for rudimentary aerial photography without going right off the bat for the fly-yourself kind of set up.

I understand and agree that usually buying cheaply just ends up expensive.  My goal is not to be "stingy", but I also know that these things have a learning curve.  I don't want to start the learning with a full return to base APM with OSD, just to (maybe) crash that because I made some simple fundamental mistake that I could have learnt using a simple (and yes, cheaper) set up from the start.

I'm approaching the FPV part of my plane in the same manner - I'm not gonna start with an expensive plane, pan/tilt/ground tracking and directional antennas, just to crash it because I didn't know the basics of interference with my radio.  I can learn that with a cheaper basic setup too.

What I basically wanted to find out, is can I start cheaply (read simply) using an UNO and build up to a fully fledged solution?  It seems the answer is a resounding "no".

Am I correct then in saying that the "bare minium" is a proper APM board without GPS.  From that I can add on and upgrade to my final goal of a full AP capable drone.

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Permalink Reply by Andre S on August 6, 2012 at 7:35am

Your approach of starting simple and then increasing complexity slowly over time makes absolute sense. Also since it is essentially impossible to avoid crashing, especially at the beginning. You didn't mention if you have RC flight experience yourself. If not it is a very good idea to learn flying first (e.g. using a free simulator) and then go on to more complicated things, since you will have to recover with manual control.

If you decide to get an APM for stabilisation do yourself a favour and invest in a GPS as well. The added price is not that big and it opens up the return-to-launch functionality which is really a saviour for initial FPV adventures (I know myself from bad experience if one relies too much on it though).

If you are not afraid to go along paths less travelled and want to stick to your Uno (and consider planes only) you could try to get some cheap IR sensors. That's the way people around here did stabilisation before all that fancy IMU stuff came along :-) I have no personal experience with that but based on what I read performance could get good.

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Permalink Reply by Etienne on August 6, 2012 at 10:14pm

I have a few years' RC flying under the belt, so can mostly keep planes in the air intact.  I have also designed and built a few planes from scratch, so can find my way around basic aerodynamics.

I don't mind tinkering, but I'm not into inventing an autopilot from first principles either.  If using the Uno is not really an option, then I will accept that.

I see some guys are building stabilization boards using Wii components and Arduino boards (though not the Uno it seems).  I always stand amazed at what human ingenuity comes up with!

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Permalink Reply by Andre S on August 2, 2012 at 10:42pm

Just to clarify what Vernon already pointed out: you essentially asked whether there is a pin-compatible IMU shield and a compatible code for the Uno and the APM. I wish there was but there is not. So if you are a beginner (like most of us, including me) and your goal is to build an autopilot using components from the DIY world then the quickest and most painless way would be to get something almost ready, like the APM. However, if you want to learn from scratch take your Uno, play around with it for a year or two (I'm serious), then read yourself into the theory and build your own board/AP. Also as Vernon pointed out, it depend a lot whether you think of planes or any sort of (multi)copter.

However, note that there are also other autopilots available, some of which are "hackable" like the APM. Google a bit and check links on the site. It's just that most people here are using this one platform and sometimes it seems that the site is a support forum for this one :-)

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