John_Mac

Progress Report on UAV DevBoard application to CCPM Helicopters


As promised, this post describes where we are in the development of the UAV DevBoard for stabilization of a CCPM Helicopter. It is still a work in progress and should not be regarded as an out-of-the-box ready-to-go system at this point.

First I want to acknowledge all the help Bill Premerlani gave in this development. Without his UAV DevBoard, his innovative DCM control formalism, and keen programming skills, this development would not have been possible.

I will take you through our development process and point out some of the pitfalls and key issues we encountered. Our hope is that others will pick up on the development and bring it to a quicker conclusion.

The progress report can be found here.

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Chris AndersonPermalink Reply by Chris Anderson on August 12, 2009 at 8:55pm
For those who don't want to download and read the pdf, the short form is that they've got it up and running on the bench, but it's unstable under power.

"This leads us to believe it is, in fact, the vibrations from the Heli producing adverse effects on either the gyros or the accelerometers. Bill has code to isolate the two and will allow us to further isolate the source of the problem."
John_MacPermalink Reply by John_Mac on August 13, 2009 at 8:19am
Initial tests on trying to isolate gyro effects from accelerometers indicate it is the gyro, but my hope is that others can test some of these results and perhaps come up with mitigating solutions. It's actually a lot of fun and I think eventually we will come up with a stable system. Still in the early phases of development.
John_MacPermalink Reply by John_Mac on August 14, 2009 at 11:45am
A couple things I am trying...

I observed some vibrations on the Heli at low RPM as I spin it up. Did some balancing of the flybar, rear rotor blades and general tightening up and made some improvements...all in the spirit of getting the vibrations down before trying to do damping.

Next I am making up some more flexible cables that run from the Rx to the Board. The Sparkfun cables are rather stiff and can transfer vibrations easily (I'm sure they are fine for normal applications). Finally, I have some foam padding to wrap the Board for further isolation. SID has given me some pointers from his experience with vibration damping which are going to be very useful.

I will also be testing with a Green Board (better gyros) that Bill is loaning me. These gyros are supposed to be less sensitive to the vibration spectrum seen with Helis. But I still want to try and make the Red Board working since it is half the price.

I will post results when I get back to this.

John
William PremerlaniPermalink Reply by William Premerlani on August 13, 2009 at 2:29pm
Hi Chris,

John and I are disappointed in the performance of the LISY gyros for helicopter applications, to say the least. Especially since Ben Levitt recently figured out how to achieve a total of 5 PWM inputs and 6 PWM outputs with the UAV DevBoard, opening up the possibility of applying the board to helis.

Certainly, I was warned in this forum that the LISY gyros are vulnerable to vibration. I was hoping that we could figure out a way to isolate the board from vibration so that helicopter pilots could use the UAV DevBoard. It is turning out to be more difficult than I thought. For example, some vibration travels along the wires!!

John is going to try a "greenboard" next. This is the $300 version of the UAV DevBoard that is no longer in production. It has Analog Devices gyros, which are supposed to be more resistant to vibration.

If the greenboard works out, I am going to ask SparkFun to revive the greenboard design, using the Analog Devices gyros that are currently available. If SparkFun agrees, then there would be two versions of the the UAV DevBoard available from SparkFun, the $150 redboard that is presently being sold, as well as a more expensive, vibration resistant clone of the greenboard.

Best regards,
Bill
Marcel SnabiliéPermalink Reply by Marcel Snabilié on September 13, 2009 at 9:14am
Hello John and Chris,

I am trying to understand and order the info I get from this site to build a UAV helicopter system in my Predator gasser.
This helicopter is now used for aerial filming with a gyro stabilized hothead.

The gas engine is giving it lot's of vibration to eliminate. This has been proven to be difficult for the image quality.

For John: Maybe overdone for you having experiance with a model helicopter, but ment well.
I do have little experience with UAV, but lot's of experiance with helicopters.
As long as there are landing crosses under the T-rex, the amplitude of the vibration on elevator and aileron is way to big to let the gyro's work. Also what i see on the picture, is that the paddles are not aligned exactly right.
First let an experianced pilot tune out the heli. This means blade balancing, no tracking at all, rather use Cf blades in this case and make sure the ESC is not on thefast throttle response.

For Chris,
I am willing to help you guys in any way i can to let you get rid of vibrations.
Just ask.

Marcel
John_MacPermalink Reply by John_Mac on September 13, 2009 at 10:09am
Hi Marcel

Thank you for the comments.

We think we have figured out the vibration problem with the Green Board, but some tests remain. The "training whees" are on during testing since there have been several instances of unexpected behavior that have benefited from the added stabililty...they really aren't the problem.

I have been flying for some time, and assure you the heli is tuned fine. The testing has gone thru several blades (and other bits and pieces) and I have been careful to balance them as well as many other components. There are no observable vibrations in flight, but the intrinsic values remain. The Red Board was VERY sensitive to these, but the Green Board gyros are much more robust. Have been in several successful stabilized hovers and forward flight with it.

We have had several storms thru here lately and have slowed my testing....hope to get more data early next week. As soon as Bill and I think we have our arms around the issues, we will release the new firmware. Happy to discuss more.

All thoughts and suggestions are appreciated.

Best,
John
Andy DemartiniPermalink Reply by Andy Demartini on August 14, 2009 at 11:04am
John,
Can you tell us which ICD2 you are using? I have an "Olimex" ICD2 (USB) from Sparkfun that will download code to my PicPilot, but it will not work as an In-Circuit Debugger. I have checked everything I can, but the vendor did not say anything about a known problem. Any chance that you are talking about the same ICD2? Thanks.
John_MacPermalink Reply by John_Mac on August 14, 2009 at 11:35am
Andy

Yes I have the Olimex ICD2. Bill says that it works for most people, but the v8.10/v7.50 problem I noted in my paper has been observed before and Olimex apparently has recognized it and come up with a fix.. I hope to be able to test the new Olimex ICD2 when it is available...and will post results.

Best
John
Andy DemartiniPermalink Reply by Andy Demartini on August 14, 2009 at 11:45am
The model here is "Olimex PIC-ICD2-POCKET".
John_MacPermalink Reply by John_Mac on August 14, 2009 at 11:47am
Andy DemartiniPermalink Reply by Andy Demartini on August 14, 2009 at 11:54am
You are using the "full-size" version, mine is the "USB".

http://www.sparkfun.com/commerce/product_info.php?products_id=8558

Do you have the info on Olimex's fix? Their web site says they will be on vacation for August. Your note is the first real hint about what might be (not) happening here.

Thanks,

Andy
John_MacPermalink Reply by John_Mac on August 14, 2009 at 12:09pm
Andy

Bill may weigh in on this...he seems to have first hand info...but it had something to do with adding some resistors to the board. Not sure it applies to your board. Sorry, just don't have that info.

Good luck
John

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