Hi everyone,

With my friend we built a solar powered glider (4m wingspan). Yesterday we made a 7 hours flight with 7800mah battery pack, the total load was 17500mah with solar cells.

It was great BUT, during the day the controler was fighting with thermals to regulate the altitude, what a waste of energy !

I tried to set the maximum sink to zero in TECS params but it didn't work. I'm sure there is a solution to let the plane taking altitude with thermals. The max climb max is set to 0,5m/s and it works great to limit the power and it is enought to lock the alti.

Maybe someone know how to let the plane free to climb but managing an altitude floor.

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Wow, amazing, would you share some of the specs of your plane ?

We will share everything,a youtube channel will show every build steps and tuning. It's powered by 12 li-ion cells (18650) and 48 solar cells C60 sunpower maxeon. APMmicro 2.7, ublox neo8m gps with compass, MPXV7002 analog airspeed sensor and genasun charge controller.

The aircraft was design by Frank Aguerre with predimRc especialy for our needs. We made the wings structure with carbon rodes and 3D printed parts made with my prusa i3.

Paul Meier said:

Wow, amazing, would you share some of the specs of your plane ?

Congrats !

APM is not really optimized for gliders, especially in the auto modes. I'm using it mostly in FBWA mode ( more details here : http://www.itluxembourg.lu/site/soaring-with-apm-and-ultimate-lrs/ )

Regarding your question about thermals in auto mode, I've noticed that the min/max pitch limits has priority over the TECS.

So here's the idea : set the LIM_PITCH_MIN to the pitch value corresponding to when your glider is just gliding at ideal speed. Let's say it's at pitch = -2°.

Now your plane is in auto mode, circling at 100 m, powered by the motor. Let's say that the pitch = 0° in this situation.

Then the plane enters a thermal : the plane takes 2 meters every second, and the APM want to correct the altitude by cutting the motor and pitching down. But it's not authorized to pitch down by more than -2° (the LIM_PITCH_MIN parameter), so it just cuts the motor, and makes a perfect glide at -2°, while continuing to gain altitude from the thermal. You'll observe that whatever settings you've got in the TECS parameters, APM will first stricly obey to the LIM_PITCH_MIN.

The thermal disappears : the plane continue its glide at -2° with motor off until 100m, loosing very slowly its altitude, and at 100m the APM throttles up again.

Maybe you'll want to change the LIM_PITCH_MIN just before landing but it's not mandatory. May I also suggest that you try to land in FBWA, trim it so that it glides correctly with sticks centered and then it becomes a perfect mode for landing almost hands off.

Thank you very much, we will work on it.

Lovely !

Cant wait for the details! :)

bravo les gars !

Wonderful, well done. How many kwh did your panels produce? How many were supplied by the battery and how many were consumed in total?

The wings are populated by 48 solar cells (sunpower C60 maxeon). They are supposed to provide more than 3w each in good conditions. So, in theory it should provide something around 150w. But the solar charger efficiency, attitude off the plane, broken cells....

For this particular flight in september with clouds:

total load:17870mah (3DR power module data)

total solar cells charge:6715 mah (frsky sensor data)

battery capacity charged after flight: 7337mah

This datas doesn't match. We need to calibrate amps meter of the power module and we think that the frsky current sensor don't work well because the value was not stable during flight.

Andreas Gazis said:

Wonderful, well done. How many kwh did your panels produce? How many were supplied by the battery and how many were consumed in total?

My skywalker and bixler consume about 4 amps @ 3S so, let's say roughly 50W to hold altitude.

How much does your motor draw?

The cells should produce enough to keep it up when the sun is high. What about battery voltage? Was it generally close to full when the sun was high? Did you start noticing the voltage starting to drop at a particular time in the day or was it being slowly being drained throughout?

paul riseborough said:

The TECS algorithm has a control parameter labelled TECS_SPDWEIGHT which controls the ratio of speed and height error affecting the demanded pitch angle. If TECS_SPDWEIGHT is set to 2.0 then the demanded pitch angle is determined by 100% by airspeed errors and 0% by height errors (height errors will be controlled via throttle) which is what you want in a thermal. If set to 0.0 then the percentages are reversed and pitch will 100% be controlled by height error (not what you want). the default is 1.0 which provides a balance between the two.

When set to 2.0 this will allow the plane to climb above the demanded height on min throttle when climbing in a thermal or descend at full throttle if in a large downdraft with the speed controlled to the set speed in both cases. Effectively the plane flies at a constant airspeed controlled by elevator and the throttle is used to control total energy. The downside is reduced precision in height control over-all and the possibility that TECS_TIME_CONST will need to be increased to get smooth height control. The TECS_PTCH_DAMP and TECS_THR_DAMP parameters can also be adjusted to compensate, but this is very trial and error unless you know how the algorithm works.

Paul (original TECS developer)

Exactly, this is also what we set (and extended) in the "passively thermal compliant" version of TECS (and also the active thermal tracking variant of it) that we use on our Pixhawk- and solar-powered glider. It is really not that tough to adapt TECS in that way, although you need to potentially take care of integrator wind up (due to the altitude error that is not being corrected). See http://diydrones.com/profiles/blogs/ackling-the-european-refugee-cr... and the papers at http://www.atlantiksolar.ethz.ch/wp-content/downloads/publications/... .

@Jean-Jacques: Great great work btw., love to see more of this!

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