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Old Apr 22, 2015, 11:05 PM
Red Cat Joe is offline
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Question
Pixhawk Autolaunch Delays

Hello all,
I'm getting a Skywalker X-8 setup with a Pixhawk.
So far, the X-8 is flying great with the Pixhawk, but now we're trying to get autolaunch working so that a single person can operate aircraft.

I've reviewed data logs from manual launches and found that the delay from the TKOFF_THR_MINACC (15m/s^2) to the aircraft reaching TKOFF_THR_MINSPD (4m/s) takes about 0.33 seconds. Am I correct in thinking that this should be the TKOFF_THR_DELAY value? (As 3.3 in the parameter)

We operate the X-8 up to 3.4kg AUW on 5s 5000mAh packs. Motor is 3548 700kv and a 11x8 Master Airscrew scimitar prop. Launches are with a 5mm bungee stretched 25-35 paces.

I'm nervous to just try it. If it's too short of a delay, it's chop-chop for someone's hand, but if it's too long the plane wont make it off the bungee.

Thanks,
Joe
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Old Apr 23, 2015, 03:45 AM
MarioSpeedwagon is offline
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Joe, I'm sorry I can't answer your question, but would you mind answering a quick one for me?

Does a rolling auto launch require any initial setup? I tried once when I first got my pixhawk setup, but haven't tried since. Motors didn't start on the ground.
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Old Apr 23, 2015, 10:51 AM
Red Cat Joe is offline
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MarioSpeedwagon,
I've never tried a rolling takeoff, but I'd think that you have to set the throttle delay, minimum acceleration, and minimum ground speed to zero.

You've probably seen this, but here's the Ardupilot wiki page on takeoffs. Rolling auto takeoffs are about halfway down the page.
Arduplane Autotakeoff

Joe
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Old Apr 24, 2015, 01:36 PM
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Thank you. I've read it, but haven't messed with it since I first set up the plane. I'll give it a go
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Old Apr 24, 2015, 06:39 PM
Red Cat Joe is offline
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Tried autolaunch today with great success.
Used 12 m/s^2 as the acceleration threshold, 3 as the throttle delay, and 4 m/s as the groundspeed.
Got three launches in; the plane is appropriately far from the thrower's hand by the time the prop spins and the launches are really solid.

The only issue is that it climbs to altitude at a nearly 50 degree deck angle. This is despite the climb pitch being set to 15 in the flight plan, and the max pitch param set to 30 degrees. Does anyone know why this might be? The current thought is that TECS is using the max throttle on takeoff and maintaining airspeed through pitch. Does that sound plausible?

Thanks,
Joe
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