He Flaps like a Bird: Destructive Resonation in Robot's Arms

KHR-1, KHR-2HV, KHR-3HV, ICS servos, RCB controllers and other Kondo products
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He Flaps like a Bird: Destructive Resonation in Robot's Arms

Post by se7en » Mon Aug 01, 2005 12:49 pm

Post by se7en
Mon Aug 01, 2005 12:49 pm

My robot has developed a symptom where his arms terribly resonate/vibrate when they move even the slightest bit. Also the symptom can be induced by flicking his hand with my finger when the robot is standing in home position. The resonation can be quite strong and makes the robot very unstable. I initially blamed this on his gyros but I removed them from the system and he still vibrates. It seems to be caused by the servo's own internal feedback, like the arm is bouncing around within the backlash in the system. I wonder if anybody knows what servo parameters I can modify to possibly control this? My first fix was to tighten the free-hones so they had a small amount of drag thus dampening the system. this worked well, but not enough, he still flaps. These strong resonant vibrations will damage the robot if allowed to persist. Has anybody else had to deal with this problem?
My robot has developed a symptom where his arms terribly resonate/vibrate when they move even the slightest bit. Also the symptom can be induced by flicking his hand with my finger when the robot is standing in home position. The resonation can be quite strong and makes the robot very unstable. I initially blamed this on his gyros but I removed them from the system and he still vibrates. It seems to be caused by the servo's own internal feedback, like the arm is bouncing around within the backlash in the system. I wonder if anybody knows what servo parameters I can modify to possibly control this? My first fix was to tighten the free-hones so they had a small amount of drag thus dampening the system. this worked well, but not enough, he still flaps. These strong resonant vibrations will damage the robot if allowed to persist. Has anybody else had to deal with this problem?
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Post by Guest » Mon Aug 01, 2005 7:09 pm

Post by Guest
Mon Aug 01, 2005 7:09 pm

A small vibration is normal. However strong vibration happens when the battery is about to be dead. When battery if full and the robot is standing in his home position for example there is still a fine vibration but nothing specially noticeable, you cannot see arms or legs moving as you describe, although you can hear the sound and can feel the vibration if you touch the robot.

If the vibration you feel is stronger than that I would avise you to replace your battery or try to charge it with another charger.
A small vibration is normal. However strong vibration happens when the battery is about to be dead. When battery if full and the robot is standing in his home position for example there is still a fine vibration but nothing specially noticeable, you cannot see arms or legs moving as you describe, although you can hear the sound and can feel the vibration if you touch the robot.

If the vibration you feel is stronger than that I would avise you to replace your battery or try to charge it with another charger.
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Post by se7en » Mon Aug 01, 2005 8:17 pm

Post by se7en
Mon Aug 01, 2005 8:17 pm

No, it is not as you describe. battery is fully charged. The slight background vibration you mention is normal, I agree. This is resonance, the hands shake like wings of a humming bird. the robots stability is affected by the strong forces. I just got him walking and this started around the 10th time I tested the walk. Problem gets worse with a stronger charge. :?
No, it is not as you describe. battery is fully charged. The slight background vibration you mention is normal, I agree. This is resonance, the hands shake like wings of a humming bird. the robots stability is affected by the strong forces. I just got him walking and this started around the 10th time I tested the walk. Problem gets worse with a stronger charge. :?
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Post by inaki » Mon Aug 01, 2005 8:39 pm

Post by inaki
Mon Aug 01, 2005 8:39 pm

Strange behaviour. My KHR1 stays absolutly static all the time, except when battery is getting very low.

You see the same behaviour on both hands so this likely is not a failure on wire connections.

I would try the following: disconnect all other servos while keeping the arms connected; is it still resonating ?
Strange behaviour. My KHR1 stays absolutly static all the time, except when battery is getting very low.

You see the same behaviour on both hands so this likely is not a failure on wire connections.

I would try the following: disconnect all other servos while keeping the arms connected; is it still resonating ?
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Video of Arms Flapping - must see!

Post by se7en » Mon Aug 01, 2005 11:58 pm

Post by se7en
Mon Aug 01, 2005 11:58 pm

I made a great little video of the arm resonance:

http://robosavvy.com/Builders/se7en/KHR1ArmShake.avi

As you can see it is quite severe. Inaki, I took your advice and disconnected all servos but the arms. He still Flaps :?
I remaved all but servos 2 and 8 ( the shoulder servos that raise the arms to the side) and he still shakes. These 2 servos are the problem. my kit is fairly recent and has KRS-786-ICS servos, maybe they have a problem? A tech from ko-propo suggested a setting I should modify in the servo software that might help. (as a side note, he confirmed that they sell a cheap digital servo that uses the same case and gears as the kondo servos, different pc board though.)

My video shows me starting the resonance with a flick of the finger. The resonance does begin on its own as soon as the robot starts moving. He battles through it and its severity is affected. Still, it causes him to fall even with gyros. before the flapping started, the walk was near perfect.
I made a great little video of the arm resonance:

http://robosavvy.com/Builders/se7en/KHR1ArmShake.avi

As you can see it is quite severe. Inaki, I took your advice and disconnected all servos but the arms. He still Flaps :?
I remaved all but servos 2 and 8 ( the shoulder servos that raise the arms to the side) and he still shakes. These 2 servos are the problem. my kit is fairly recent and has KRS-786-ICS servos, maybe they have a problem? A tech from ko-propo suggested a setting I should modify in the servo software that might help. (as a side note, he confirmed that they sell a cheap digital servo that uses the same case and gears as the kondo servos, different pc board though.)

My video shows me starting the resonance with a flick of the finger. The resonance does begin on its own as soon as the robot starts moving. He battles through it and its severity is affected. Still, it causes him to fall even with gyros. before the flapping started, the walk was near perfect.
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Post by inaki » Tue Aug 02, 2005 1:42 am

Post by inaki
Tue Aug 02, 2005 1:42 am

Oh my! The effect is worse that I expected. Nothing to do with the 'low battery' effect.

I use the 784 servo model in all places but the head, where I have a 786.
The 786 has some features that 784 does not have so I wonder whether the RCB is causing some problem here.

I suppose you have not tweaked these motors with the ICS interface ?

By the way, what is that circuit on the chest of your KHR1 ? Just curious.
Oh my! The effect is worse that I expected. Nothing to do with the 'low battery' effect.

I use the 784 servo model in all places but the head, where I have a 786.
The 786 has some features that 784 does not have so I wonder whether the RCB is causing some problem here.

I suppose you have not tweaked these motors with the ICS interface ?

By the way, what is that circuit on the chest of your KHR1 ? Just curious.
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Post by Meltdown » Tue Aug 02, 2005 12:15 pm

Post by Meltdown
Tue Aug 02, 2005 12:15 pm

I have had the "flapping" as well, seems to come and go.
Maybe changing the dead-band of the affected servos to a wider setting will help, haven't tried myself yet.
I have had these symptoms with rc car racing a lot.
It was always a potmeter problem. It seems like the potmeter of the servo can't find it's center anymore.
Cleaning the potmeter sometimes helped but i always wound up exchanging it in the end.
The carbon strip in the potmeter could also be damaged resulting in sending out erratic resistance values.
Or the tiny contacts which go over this carbon strip could be slightly bend resulting in the same effect. Remember that the main chaft is connected directly to the potmeter. There's no bearings to stiffen up the sideway forces subjected to it. It can easely bend.
Then again it could be something completely different.

Try to exchange the servo for another one and see if the shoulder still flaps.
If it does it's not servo related.
I have had the "flapping" as well, seems to come and go.
Maybe changing the dead-band of the affected servos to a wider setting will help, haven't tried myself yet.
I have had these symptoms with rc car racing a lot.
It was always a potmeter problem. It seems like the potmeter of the servo can't find it's center anymore.
Cleaning the potmeter sometimes helped but i always wound up exchanging it in the end.
The carbon strip in the potmeter could also be damaged resulting in sending out erratic resistance values.
Or the tiny contacts which go over this carbon strip could be slightly bend resulting in the same effect. Remember that the main chaft is connected directly to the potmeter. There's no bearings to stiffen up the sideway forces subjected to it. It can easely bend.
Then again it could be something completely different.

Try to exchange the servo for another one and see if the shoulder still flaps.
If it does it's not servo related.
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Problem Solved

Post by se7en » Tue Aug 02, 2005 1:35 pm

Post by se7en
Tue Aug 02, 2005 1:35 pm

The deadband is what the tech had me adjust first; it had no effect. then I played with the punch which did nothing as well. Then I noticed a choice between two types of dampening. I chose the type with a slight overshoot and this completely eliminated the vibration! I did this to all of the arm servos and now it runs nice and smooth. I think I will change this setting on all of the remaining servos.

Inaki, the circuit on the robots chest is just his gyro. I didn't want to squeeze it in the back cover. if you look under his right arm you see the other gyro.
The deadband is what the tech had me adjust first; it had no effect. then I played with the punch which did nothing as well. Then I noticed a choice between two types of dampening. I chose the type with a slight overshoot and this completely eliminated the vibration! I did this to all of the arm servos and now it runs nice and smooth. I think I will change this setting on all of the remaining servos.

Inaki, the circuit on the robots chest is just his gyro. I didn't want to squeeze it in the back cover. if you look under his right arm you see the other gyro.
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Post by robosavvy » Wed Aug 10, 2005 12:43 pm

Post by robosavvy
Wed Aug 10, 2005 12:43 pm

Finally got an answer from Japan for what could potentially cause the paranormal flapping phenomena:

- voltage to supplied the robot could be too high
- Using the PC cable interface, you may have set the Gain with a value that's too high.
Finally got an answer from Japan for what could potentially cause the paranormal flapping phenomena:

- voltage to supplied the robot could be too high
- Using the PC cable interface, you may have set the Gain with a value that's too high.
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Heavy shaking servos

Post by noDNA » Thu Mar 23, 2006 3:21 pm

Post by noDNA
Thu Mar 23, 2006 3:21 pm

Hi all,
yes se7en, you are right. I had the same very heavy shaking of arm servos.
Makes you getting afraid that the servos will break because of this resonance movement.

The only way I know to ged rid of it is to use the ICS Servo Manager and the ICS PC serial cable with two ends, (both same pins), one end supplies power ( I use a lab power supply, 6V, black is ground, red is 6V, instead of RCB-1 power) and the other end goes ito the servo that should be reprogrammed.

After selecting the COM port you can read the settings from the servo and store them for future use in a file.

Then select the DAMPING curve with the overshoot (1) instead of the preset slope (2).

That should solve it immediately. Did so with mine. By the way, happened to me only with the new KRS786 (red) servos, not with the old 784(blue) servos.

Disadvantage is you need the ICS Servo programmer kit. No way to solder your own cable. Has some chep electronics in there but too complicated for a user to assemble it himself. Need to be experienced. I have images of the internal PCB if someone is interested.
regards
noDNA
Hi all,
yes se7en, you are right. I had the same very heavy shaking of arm servos.
Makes you getting afraid that the servos will break because of this resonance movement.

The only way I know to ged rid of it is to use the ICS Servo Manager and the ICS PC serial cable with two ends, (both same pins), one end supplies power ( I use a lab power supply, 6V, black is ground, red is 6V, instead of RCB-1 power) and the other end goes ito the servo that should be reprogrammed.

After selecting the COM port you can read the settings from the servo and store them for future use in a file.

Then select the DAMPING curve with the overshoot (1) instead of the preset slope (2).

That should solve it immediately. Did so with mine. By the way, happened to me only with the new KRS786 (red) servos, not with the old 784(blue) servos.

Disadvantage is you need the ICS Servo programmer kit. No way to solder your own cable. Has some chep electronics in there but too complicated for a user to assemble it himself. Need to be experienced. I have images of the internal PCB if someone is interested.
regards
noDNA
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Post by se7en » Fri Mar 24, 2006 2:56 am

Post by se7en
Fri Mar 24, 2006 2:56 am

Yes Nodna, you figured it out. That is the solution I posted a long time ago. I think these servos are just bad. My robot has been suffering from unsteady movements ever since, and slowly getting worse.
Yes Nodna, you figured it out. That is the solution I posted a long time ago. I think these servos are just bad. My robot has been suffering from unsteady movements ever since, and slowly getting worse.
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Post by Toukisarchu » Fri Apr 07, 2006 8:00 am

Post by Toukisarchu
Fri Apr 07, 2006 8:00 am

I cant offer any help but OMG those are some bad shakes. I didnt even know servos could move like that. GL with figuring it out
I cant offer any help but OMG those are some bad shakes. I didnt even know servos could move like that. GL with figuring it out
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Post by Meltdown » Tue Apr 25, 2006 4:12 am

Post by Meltdown
Tue Apr 25, 2006 4:12 am

The flapping is back with a vengeance.
Always the same servos (both shoulders sideways)
Changing the dampening setting doesn't work for me either.
Tried every servo manager combination.
Don't know how to solve it. ':cry:'
The flapping is back with a vengeance.
Always the same servos (both shoulders sideways)
Changing the dampening setting doesn't work for me either.
Tried every servo manager combination.
Don't know how to solve it. ':cry:'
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Post by noDNA » Wed Apr 26, 2006 8:27 am

Post by noDNA
Wed Apr 26, 2006 8:27 am

Perhaps we can get down to the real problem of the Flapping.

Meltdown, if you exchange the servo cables of the shoulder and hand
does the flapping occur still in the shoulder or is it in the hand?

The question is: is it really a servo problem or a servo controller problem? In my case, I assumed it was a servo problem because using the Servo Manage I was able do damp it away. But now I am not too sure anymore because it seems to occur with different KHR-1s of different users and it is (always?) in first and/or second arm servo (shoulder rotate and up/down)

kind regards
noDNA
Perhaps we can get down to the real problem of the Flapping.

Meltdown, if you exchange the servo cables of the shoulder and hand
does the flapping occur still in the shoulder or is it in the hand?

The question is: is it really a servo problem or a servo controller problem? In my case, I assumed it was a servo problem because using the Servo Manage I was able do damp it away. But now I am not too sure anymore because it seems to occur with different KHR-1s of different users and it is (always?) in first and/or second arm servo (shoulder rotate and up/down)

kind regards
noDNA
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Post by Ray » Wed Apr 26, 2006 12:56 pm

Post by Ray
Wed Apr 26, 2006 12:56 pm

:( Oh! it is frustrating that Some KRS-784 have these problem,
Is there no method if I do not have a servo program?

Do Robonova-I has the same problem?

:roll:
:( Oh! it is frustrating that Some KRS-784 have these problem,
Is there no method if I do not have a servo program?

Do Robonova-I has the same problem?

:roll:
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