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Permalink Reply by Marianne Antonio on September 29, 2011 at 8:25pm

Randy, you are using futaba gy401 right? what is your gyro gain?

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Permalink Reply by Marianne Antonio on September 30, 2011 at 2:05am

Hi malcolm, what's your gyro? We are currently having a problem with ours. The gyro works perfectly when connected to the receiver, but it doesn't initialize when connected to the apm. Any ideas? We changed our gyro to gy401 (futaba) with gyro gain of 1672.

 

Basically the gyro reacts at the first movement, then the tail goes back to the original position, and then there will be no more movement after.

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DeveloperPermalink Reply by Randy on September 30, 2011 at 5:27am

maybe you could try switching the servo types to analog?  or change the SV_AVG average to 5 using AP_MissionPlanner.  I'm grasping at straws but perhaps it's again the update rate.

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Permalink Reply by malcolm churn on September 30, 2011 at 6:14am

The 401 gyro works on either side of the middle point so if the you have 1000 - 2000 then 1500 is the centre, the gyro will give no control @1500 as you move either way it will go into heading hold or Normal mode, but i dont know which way is which.

If you say that it is returning to center at 1672 then go below 1500 and try around 1350 and see what it does then, you should be in AVCS mode (heading Hold).

 

found this on another site might explain it better

 

 Servo Throw (PWM) = mode, gain                       :  examples:
-- 100% (2.0 ms PWM) = heading hold, 100% gain
--   90% (1.9 ms PWM) = heading hold, 80% gain
--   80% (1.8 ms PWM) = heading hold, 60% gain     :  if you want 60% gain in heading hold mode, you need 50% + (.6 * 50%) = 80% total throw.
--   70% (1.7 ms PWM) = heading hold, 40% gain
--   60% (1.6 ms PWM) = heading hold, 20% gain
--   50% (1.5 ms PWM) = 0% gain
--   40% (1.4 ms PWM) = rate mode, 20% gain
--   30% (1.3 ms PWM) = rate mode, 40% gain         :  if you want 40% gain in rate mode, you would need 50% - (.4 * 50%) = 30% total throw.
--   20% (1.2 ms PWM) = rate mode, 60% gain
--   10% (1.1 ms PWM) = rate mode, 80% gain
--     0% (1.0 ms PWM) = rate mode, 100% gain

 

Set you gain to 60% which according to the table above is around 1800, the reason you had little or no response is because you were too low with your gain channel. If you still see no heading hold but your gyro is working in rate mode then reverse the channel or go below 1500 to 1200 hope that helps

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Permalink Reply by malcolm churn on September 14, 2011 at 11:58am

@Randy, my ACM does not seem to be logging CTUN, any ideas?

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DeveloperPermalink Reply by Randy on September 15, 2011 at 8:01am

malcolm,

     It looks like in the latest code like you need to arm the motors in order for CTUN to be dumped to the logs.  I haven't looked into exactly why that's the case yet.

     You can "arm the motors" by putting collective pitch to zero and yaw fully right.  You should see the lights on the front of the APM flash very rapidly and you'll temporarily be unable to move the servos...but control will return after about 5 seconds.  I believe this will also initialise the barometer so it's not a completely bad thing.

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Permalink Reply by malcolm churn on September 16, 2011 at 1:30am

Thanks randy, i'll try it tonight when i get home :)

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Permalink Reply by Graham on September 20, 2011 at 2:26am

I was telling you all earlier about the problems I had with drift (the heli would gradually roll or pitch more and more and would require more stick input just to keep it level).  I haven't had a chance to fly it again or try the hardware filter jumpers as previously suggested since I have been on vacation.  I have however looked into the logs in more detail.  It appears that the accelerometers are the cause and I suspect vibration.  See the attached log.  It shows the z axis accel (in blue) go from the correct value of 9.8 to an average of ~5 after takeoff.  I was only flying in a steady hover so I wouldn't expect this value to change much.  The other accelerometer values also shift slightly as well.  Therefore I am pretty sure that the source of my issues are erroneous accelerometer values due to helicopter vibrations that cause the gyro drift correction to incorrectly compensate.  I checked the gyro values and they seem to be reasonable.

 

When I get back I will try enabling the hardware filters for the accelerometers and/or eliminate any sources of vibration.  Just wanted to share this with anyone who might also be having a drift issue in case it might help.  If you have a problem please post you log files or an example plot so we can compare the behaviour we are observing.

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Permalink Reply by Graham on September 20, 2011 at 2:44am

Here is one of my log files.  Note that all of my logs show the same behaviour.  The z-accel changes from 9.8 to 5  and the signal gets very noisy after the motor is spun up.

Attachments:

• 2011-08-31 07-15 1.log, 884 KB

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DeveloperPermalink Reply by Randy on September 20, 2011 at 5:22am

Graham,

     Interestingly I had the same problem last weekend and it was 100% caused by vibration.  I partially broke a main propeller and had to replace it with another which, although very similar, was slightly heavier.  This caused a visible shake especially when spinning up the motor.  I didn't record the logs but I certainly found I had to pull back harder and harder on the pitch as time went by.  landing sorted it out temporarily but as soon as i took off the pull would begin again.  After sorting out the main blades all was well again.

     How are you mounting the APM to the frame?  I use plastic screws with little rubber washers so that the screw never directly contacts the APM (or not much).

    

-Randy

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Permalink Reply by Graham on September 20, 2011 at 2:37pm

Glad to hear I am not alone :)  I am using double sided gyro tape to mount my APM to a CF plate.  Do you think the screws/washers would be better?  Have you done both?

 

By 'sorting out' the main blades, do you mean you balanced them?  Or did you do something else?

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DeveloperPermalink Reply by Randy on September 20, 2011 at 5:39pm

I haven't used gyro tape, I would have thought that that would have worked.  Maybe it's just not thick enough and you should double up?  Originally I was so paranoid of vibration I actually sandwiched the APM between two 1cm think pieces of foam so it was basically "floating" with no hard connections to the frame at all.  That flew a-ok but I eventually found it was unnecessary and went to the above approach.

 

Somewhere I once found this vibration foam that was described as having "the consistency of meat" and on Japanese TV the other day I saw a material so shock absorbant (and sticky) that you could pelt a raw egg at it (from a 45 degree angle) and the egg wouldn't break, it would just stick to the material.

 

I'm going to add "get vibration mounts" to my list of hardware to gather up and make available for people to help them get started more quickly.

 

To resolve my issue, I put the heavy blade back on the shelf and replaced it with one that was much closer to the weight of the remaining blade.

 

 

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