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[Paparazzi-devel] Re: Paparazzi UAV Project

From: Hugo Vincent
Subject: [Paparazzi-devel] Re: Paparazzi UAV Project
Date: Fri, 16 Apr 2004 21:34:42 +1200

Hello again Antoine,

I forgot to ask you what your main flight sensors are now, with the CerfBoard configuration? Are you still using the Infrared sensors, or have you moved across to the inertial type, gyros and accelerometers?

On 16/04/2004, at 7:42 PM, address@hidden wrote:

Selon Hugo Vincent <address@hidden>:

Hi Hugo

Hi Antoine,

Thanks for your prompt reply. I will check the CVS again in a week or
two, and look forward to seeing what you have been up to.

Would it be fair to say that you are moving more to the AUTOPILOT
topology - I mean with the Linux board and so on?

Do you think there is still a need for two AVRs when you have a
CerfBoard? What sort of interface are you using to talk to the AVR from
the ARM CPU. (BTW, XScale == (ARM + extensions))

I Like the idea of having two avrs:

- For robustness : the code in the small avr is short, well tested and frozen.
   If you put a bug in the big avr where the code is bigger and more
complicated, you will still get manual control, health supervision and failsafe.

- the parameters of the small MCU are tuned during the first test flight of an airframe and never changed after that. So, no risk of trashing these vital
settings when playing with autopilot gains and flashing the big MCU

- another advantage is that it gives alot of spare "power" in the small avr to implement PCM decoding ( I think we really need that ) and lets you be less
"realtime" in the big avr.

- we want to keep developing the avr-only system because is is simple, cheap, light and has a low power comsumption. It is very well suited for the smallest
aircraft. We intend to fit one in a 300g airframe.

wow, 300g!!
Like i said, i am new to RC, so: what is the advantage of PCM? just better range and signal quality? or something more subtle...

We are using RS232 to talk between the big avr and the cerfboard.

I am going to buy a cheap airframe real soon -- do you recommend the
Twin Star? I am kind of put off by the twin motors.

The twinstar is a good airframe. It flies well and is very "heavy duty". The
"high wing - twin engine" configuration has advantages and drawbacks.

advantages : it leaves space in the fuselage - namely in the nose of the aircraft - it is very handy to put the camera and the video transmitter.
it protects the motors and propeller during belly landings.
it's easy to hand launch

drawbacks : if you want to use high end motor, you'll have to buy two... if you want to use brushless motors you'll need two controllers. Generally
speaking, one big motor has a better efficiency than two small.

Approximately what
is the payload weight capacity of that airframe?

well... it depends. With a 8*2400mAh nicd, it weights about 1300g. We have flow
one up to 1600g.
I would say payload is between 200g and 500g depending on battery weight.

ok, how much of the 1300g is batteries?

Also, what
approximately is the battery life like?

What do you mean life ? for flight duration, with the stock electric motor, we get 17 minutes with a 8x2400mAh nicd packs. We also have a 8x3300 nimh (same
weight as previous pack) which give 25 minutes flight.

We have buit a new fuselage with 2P3S 2000mAh lipo. It shoud give much longer flight time. We are also working on a new wing with brushless motors to further
improve flight time.

For how the battery behave in time. Nicd tend to be robust and last long. NiMh tend to be more fragile (last less than a year, maybe 100 cycles). We have very
little experience with lipo cells.

I did a project at work with Lithium Ion cells on a handheld computer design we were working on -- a charger and power supply unit. At least with the cells we were using, they prefer constant, lower current draw, i.e. not 30A, and not on-and-off, but if they had to, they can supply fairly the high currents. I am not 100% sure about the differences between LiIon and LiPo, but have heard LiPo have a shorter life cycle (# of charges) but have a better energy density. I have heard that after around 1000 charges for LiIon or 500 charges for LiPo, the total capacity is about 1/2 of what it was new. I would guess that high discharge rates would decrease them somewhat.

For comparison, the RCtoys Predator ( apparently runs 1 hr 30 min on LiPo, and 16-20 min with the NiCad. There battery pack is 7.4V, 4200mAh, for US$139. A quick look at which sells (among other things), surplus Nokia LiIon cells of 3.6V and 1200mAh capacity for about US$13. So 6 of them for about US$80 would give 10.8V and 4400mAh!!! Maybe too heavy though.

The charging is a lot more complicated for Lithium, than for Nickel cells. But you can get nice single chip solutions to do it (we used the MAX1649 + an ATtiny micro).

I am definitely keen on getting
started with an electric model.

Would I really need a test pilot? Can I just teach myself to fly it :)

It's you to see, but it may take a little time before you are confortable with
I think an experienced pilote will better handle the emergency situations that might occur during initial test flights. Furthermore, it is very handy to be two. One will keep his eyes on the airplane, the second one on the laptop screen.

If i were you, i would buy two aircraft. A small one like a multiplex pico cub to teach you flying and a second one like a twinstar to test flight your autopilot.
Are there any other airframes that you have been eyeing up, thinking, "that would be perfect for this project"?
I'm sure you will be less stressed when you learn to fly if you don't risk your
precious electronic toys (GPS camera cerfboard).

Anyway, I think it's a good idea to have contacts with a modele aircraft club. People there know well how to build/fly model airplanes and it will save you
time and money.
I agree. I am working on it...

If you are offering, I would really appreciate a blank PCB -- they are
unreasonably expensive to get made over here in NZ.

I will send you one when its done, in a couple of week. It will be a panel with several PCBs (ground_modem, programmer, ir_sensor, ctl_board, power_supply, GPS).

Maybe you'll want to review the routing/design before i send it to fab.

Maybe we could continue this discussion on the mailling list so that other can



Hugo Vincent

On 15/04/2004, at 7:49 PM, address@hidden wrote:

Hi Hugo

Selon Hugo Vincent <address@hidden>:

Hi Antoine,

I am a university student in New Zealand, currently in third year
Electrical/Computer Engineering. I am planning a UAV project as a
project, and part of it would be my thesis. I have been writing a
document describing some of the aspects of it, that I have attached.
Lots of things in it are wrong or incomplete or subject to change, but
you'll get the general idea. I am looking at using an AVR and an ARM
processor, with a similar topology to your paparazzi system (AVR for
real-time stuff- RC reception, servos, etc., and the ARM for
and stabilization). I am new to RC aircraft and don't really know
to look, but I have experience with the electronics and software sides
of things.

That is a very good news. I have some experience with RC aircraft but
less with
electronics :)

If you are new to RC aircraft, you will need a test pilot for your
Maybe you should look for a local RC aircraft club.

Regarding the topology of our project, we use a 3 levels/processors

We have a small avr mega8 mcu which is responsible for radio control
servos actuating and low level monitoring (like battery). With this
MCU alone,
you are able to fly the model in manual mode.

We then have a second MCU, an avr mega128, wich is responsible for
(ADCs, compass etc...), low level control loop, telemetry transmition,
With both MCU's our aircraft if capable of fully autonomous navigation.

We intend to expend the system with a third high level processor which
allow intensive computation and network communication. We have an arm
cerfboards running Linux that is almost ready to test flight. We
intend to
connect it to a 800MHz radio modem (coronis wavecard
and to our real time controller board.

I just found about your project today, and have been reading the
mailing list archives etc. It seems you project might be headed where
my one wants to begin, at least in terms of electronics and
processors... I am more interested in a longer duration (therefore gas
powered) airframe, but an electric drive is so appealing for
convenience reasons...

The airframe is not really important at first. Use something cheap and
to devellop your autopilot. When it's done, you can then mount it on a
sophisticated airframe.
We use the twinstar because it flies well, is cheap, can fit in the
car, doesn't
need a runway etc... Someday, when i have time, i will mount a
autopilot in one of my gas aircraft.

I would be most interested in your views and opinions about my ideas,

I think your project is heading in the good direction.

and maybe the possibility of working together. I look forward to
hearing back.

Working together would be great!
We have spend past weeks writting documentation, reorganizing code and
user interface. I will update savannah in the following days and
announce it on
the mailing list.

I am now designing a new version of the controller board. I intend to
have PCBs
build by eurocircuits. I could send you one of these when they are




Hugo Vincent

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