Altitude hold for UAV DevBoard

UAV DevBoard pilots,

I am putting the most recent releases of MatrixNav and AileronAssist back on line. I briefly reverted to the previous releases while I investigated a system issue that I just ran into.

I just bought an EasyStar, ready to fly, with radio, servos, ESC, and radio already installed. I did some flying with MatrixNav. Most of the time it worked fine, but once in a while there were problems that popped up at random. Once in a while the firmware believed the radio signal is lost, and reverts to return to launch mode. Sometimes the elevator will work in only "bang-bang" control mode, responding to manual control by going either full up or full down. Typically, the problems arise at random, after about 10 minutes of flying.

After some investigation, I discovered a system issue that a few of you have already run into. It turns out that low battery voltage will cause a "brownout" situation for the CPU. It turns out there was a problem with the ESC. Although the CPU did not reset, some of the hardware configuration registers reverted to their default values. This will cause the firmware to think the radio signal is lost, and it will go into return to launch mode. This will happen with any of the releases of MatrixNav or AileronAssist.

When I have some time, I will take a closer look at handling low battery voltage.

In the meantime, be sure to use good batteries and a quality ESC.

Best regards,
Bill Premerlani

Altitude hold is now available as an option in the most recent releases of the control and navigation firmware for the UAV DevBoard, MatrixNav1.7, and AileronAssist1.6. Both are available from the UAV DevBoard home page.

The altitude hold function has been tested by both Sid and myself. According to Sid, it is "precise".

During my tests, AileronAssist was able to hold my Goldberg Endurance in a turn at a 45 degree bank angle, at constant altitude, for 30 minutes.

Next, I am going to implement waypoints.

Best regards,
Bill Premerlani

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Comment by OlivierD. on August 28, 2009 at 7:31pm: Wow ! Bill, that is amazing! I've had to put my UAV projects on the back burner for a bit but that is something to look forward to when I get back to it! Many thanks.

Comment by William Premerlani on August 28, 2009 at 7:52pm: OlivierD,

Thanks for the kind words.

Altitude was something that I thought that I would "just do", but it took much longer than I thought, because it took a while for Sid and myself to realize that the response of the LISY gyros to vibration was limiting the precise pitch control that I was counting on. It wasn't until I started to work with JohnMac on stabilizing his helicopter that I really started to think about vibration, and make some measurements of my own.

Once we appreciated that vibration could be an issue for fixed wing applications as well as for helicopters, we paid more attention to it, came up with some simple solutions, and then altitude hold was easy to implement.

In the process of implementing altitude hold, I added pitch rate damping, based on the rate of change of the earth frame of reference pitch, which is not the same thing as the output of the pitch rate gyro. You need some of the elements of the direction cosine matrix to compute it from the raw gyro signals.

The resulting pitch stabilization in the latest versions of the firmware is very smooth and precise, even in the face of gusty winds.

Best regards,
Bill

Comment by Peter Meister on August 29, 2009 at 12:11am: WAY TO GO BILL!!! Awesome, I downloaded it this evening and I am testing it out tomorrow. Awesome, and now Waypoints are coming, this is incredible... Thanks for all the hardwork on this...

Comment by William Premerlani on August 29, 2009 at 3:37am: Hi Peter,
Thank you.
Sailplane pilots are going to find altitude hold particularly useful. They can set it up to shut the motor off and optimize glide angle in a thermal or slope lift, and to turn the motor back on and climb back up if the plane gets too low.
Best regards,
Bill

Comment by jonny on August 30, 2009 at 1:59pm: Bill
Impressive stuff, does this work with the older green board? Please keep up the good work
Kindest regards
Jonny

Comment by tycinis on August 30, 2009 at 2:17pm: How long you think to implement Waypoint ?

Benjamin

Comment by William Premerlani on August 30, 2009 at 2:28pm: Jonny,

Both MatrixNav and AileronAssist will work with either the red board or the green board. There are two projects in the zip file, a "green" project and a "red" project, which take care of the minor differences between the two boards.

By the way, Jonny, were you the person who asked me about ailerons and rudder a month or two ago? Since then, Ben Levitt has figured out how to use the spare pins on the board to implement 5 PWM inputs and 6 PWM outputs. So, sooner or later someone will probably develop firmware to control rudder, elevator, ailerons, and throttle.

Best regards,
Bill

Comment by William Premerlani on August 30, 2009 at 2:30pm: Hi tycinis,

My goal is to finish waypoints by the end of September. Depending on the flying weather, it may take more or less time than that.

Best regards,
Bill

Comment by jonny on August 31, 2009 at 2:43am: Hi Bill
Thank you for the reply, thats good news as I would like to try the altitude hold.
It was indeed me who enquired about rudder input with the aileron assist and my predicament is even more dire than it was two months ago, I have now completed the airframe that was intended to be used for experimenting with the UAV DevBoard, but so far, all it has been good for is keeping my heart rate above 100 whilst flying it! I havent had much time for tweaking yet but it is very techy in a turn, requiring a substantial amount of concentration.
Work commitments are dictating the ammount of time I can spend on this at the moment, but as soon as things ease up I hope to be integrating the green board to this plane, also I plan to use the red board in a sailplane with rudder/elevator control and RTL.

Once again Bill, Many thanks for the reply and I hope not to be too much of a nuisance when when I start

Kind regards
Jonny

Comment by William Premerlani on August 31, 2009 at 3:44am: Jonny,

Have you tried using aileron assist in stabilize mode to reduce your workload?

Without rudder control, return-to-launch mode would not work, but in stabilize mode, aileron assist could be useful. You would still need to control the rudder entirely yourself, but aileron assist will stabilize pitch and roll enough through inputs to ailerons and elevator to get your heart rate down to a more reasonable level. In particular, if you get into trouble, you can take your hands off the controls and aileron assist will recover for you.

Best regards,
Bill

Altitude hold for UAV DevBoard

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