Tuning Recipe - Revision history

OlliW: /* Balancing the Gimbal */

2015-09-14T14:46:47Z

Balancing the Gimbal

← Older revision		Revision as of 16:46, 14 September 2015
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	The video shows a well balanced gimbal. Here it is possible to move the camera to any orientation and let it free, without it turning back to a preferred orientation.		The video shows a well balanced gimbal. Here it is possible to move the camera to any orientation and let it free, without it turning back to a preferred orientation.

	~~Some further~~ tips:		Please also consider these tips:
	* It is {{WARNING\|'''important'''}} to electrically disconnect the motors from the board, since then they can rotate more freely than just being disabled in the GUI.		* It is {{WARNING\|'''important'''}} to electrically disconnect the motors from the board, since then they can rotate more freely than just being disabled in the GUI.
	* A much more severe test to check balance is to heavily shake the gimbal, up and down, left and right, forward and backward. When balanced, the camera will stay in the position it was before the shaking started. Do this for different camera positions.		* A much more severe test to check balance is to heavily shake the gimbal, up and down, left and right, forward and backward. When balanced, the camera will stay in the position it was before the shaking started. Do this for different camera positions.

OlliW: /* Balancing the Gimbal */

2015-09-14T14:46:21Z

Balancing the Gimbal

← Older revision		Revision as of 16:46, 14 September 2015
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	Some further tips:		Some further tips:
	* It is ~~better~~ to electrically disconnect the motors from the board, since then they can ~~move~~ more freely than just being disabled in the GUI.		* It is {{WARNING\|'''important'''}} to electrically disconnect the motors from the board, since then they can rotate more freely than just being disabled in the GUI.
	* A more severe test to check balance is to heavily shake the gimbal, up and down, left and right, forward and backward. When balanced, the camera will stay in the position it was before the shaking started. Do this for different camera positions.		* A much more severe test to check balance is to heavily shake the gimbal, up and down, left and right, forward and backward. When balanced, the camera will stay in the position it was before the shaking started. Do this for different camera positions.
	* A 3-axis gimbal requires more precise balancing than a 2-axis gimbal. Especially the yaw axis needs attention.		* A 3-axis gimbal requires more precise balancing than a 2-axis gimbal. Especially the yaw axis needs attention.
	* In general, the smaller the camera the more important is the balance.		* In general, the smaller the camera the more important is the balance.

OlliW: /* Balancing the Gimbal */

2015-09-14T14:43:31Z

Balancing the Gimbal

← Older revision		Revision as of 16:43, 14 September 2015
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	Before any tuning, the gimbal needs to be balanced. Balancing means to bring the center of gravity (COG) of the mounted camera into the center of all three gimbal motor axes (depending on the gimbal construction it is also part of the balancing to ensure that all three gimbal motor axes cross in one point). A quick test, which may be sufficient for larger cameras, is to move the camera by hand while all gimbal motors are turned off: The camera should remain in its position whenever you let it go, as demonstrated in the video below.		Before any tuning, the gimbal needs to be balanced. Balancing means to bring the center of gravity (COG) of the mounted camera into the center of all three gimbal motor axes (depending on the gimbal construction it is also part of the balancing to ensure that all three gimbal motor axes cross in one point). A quick test, which may be sufficient for larger cameras, is to move the camera by hand while all gimbal motors are turned off: The camera should remain in its position whenever you let it go, as demonstrated in the video below.

	A perfectly balanced gimbal has many advantages. Otherwise:		A perfectly balanced gimbal has many advantages. Otherwise you will get artefacts:
	* When the gimbal as a whole is accelerated, the camera would rotate out of position due to residual forces - see the image below.		* When the gimbal as a whole is accelerated, the camera would rotate out of position due to residual forces - see the image below.
	* The motors need to apply more power to keep the camera in position.		* The motors need to apply more power to keep the camera in position.
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	* Vibrations in the gimbal are more easily induced.		* Vibrations in the gimbal are more easily induced.

	Balancing not only brings advantages, a ~~certain~~ degree of balancing is in fact mandatory for the gimbal and controller to function at all. It's as simple as that: The better the balancing the better the gimbal performance. This holds true especially for a 3-axis gimbal.		Balancing not only brings advantages, a minimu degree of balancing is in fact mandatory for the gimbal and controller to function at all. It's as simple as that: The better the balancing the better the gimbal performance. This holds true especially for a 3-axis gimbal.

	You will always have to compromise, because e.g. the gimbal does not allow for infinitely precise adjustments, or because of friction in the motors, and so on. Hence take considerable effort in balancing the gimbal as good as possible, but at some point one of course has to let go.		You will always have to compromise, because e.g. the gimbal does not allow for infinitely precise adjustments, or because of friction in the motors, and so on. Hence take considerable effort in balancing the gimbal as good as possible, but at some point one of course has to let go.

OlliW: /* Balancing the Gimbal */

2015-01-30T03:58:46Z

Balancing the Gimbal

← Older revision		Revision as of 05:58, 30 January 2015
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	You will always have to compromise, because e.g. the gimbal does not allow for infinitely precise adjustments, or because of friction in the motors, and so on. Hence take considerable effort in balancing the gimbal as good as possible, but at some point one of course has to let go.		You will always have to compromise, because e.g. the gimbal does not allow for infinitely precise adjustments, or because of friction in the motors, and so on. Hence take considerable effort in balancing the gimbal as good as possible, but at some point one of course has to let go.

	The picture below shows a badly balanced situation. The center of gravity is quite below the pitch motor axis. At first this might actually look like a good idea, since the camera gets "self-stabilized" by gravity. However, consider now the gimbal being accelerated to the right. Because the center of gravity is below the pitch axis, where would be a force on the camera and it would tilt downwards. The PID controller would have to fight against that, which makes it much harder or even impossible for it to stabilize the camera.		The picture below shows a very badly balanced situation. The center of gravity is quite below the pitch motor axis. At first this might actually look like a good idea, since the camera gets "self-stabilized" by gravity. However, consider now the gimbal being accelerated to the right. Because the center of gravity is below the pitch axis, where would be a force on the camera and it would tilt downwards. The PID controller would have to fight against that, which makes it much harder or even impossible for it to stabilize the camera.

	The video shows a well balanced gimbal. Here it is possible to move the camera to any orientation and let it free, without it turning back to a preferred orientation.		The video shows a well balanced gimbal. Here it is possible to move the camera to any orientation and let it free, without it turning back to a preferred orientation.

OlliW: /* Balancing the Gimbal */

2015-01-30T03:58:14Z

Balancing the Gimbal

← Older revision		Revision as of 05:58, 30 January 2015
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	Some further tips:		Some further tips:
	* It is better to ~~physically~~ disconnect the motors from the board, since then they can move more freely than just being disabled in the GUI.		* It is better to electrically disconnect the motors from the board, since then they can move more freely than just being disabled in the GUI.
	* A more severe test to check balance is to heavily shake the gimbal, up and down, left and right, forward and backward. When balanced, the camera will stay in the position it was before the shaking started. Do this for different camera positions.		* A more severe test to check balance is to heavily shake the gimbal, up and down, left and right, forward and backward. When balanced, the camera will stay in the position it was before the shaking started. Do this for different camera positions.
	* A 3-axis gimbal requires more precise balancing than a 2-axis gimbal. Especially the yaw axis needs attention.		* A 3-axis gimbal requires more precise balancing than a 2-axis gimbal. Especially the yaw axis needs attention.

OlliW at 20:36, 10 January 2015

2015-01-10T20:36:51Z

← Older revision		Revision as of 22:36, 10 January 2015
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	The picture below shows a badly balanced situation. The center of gravity is quite below the pitch motor axis. At first this might actually look like a good idea, since the camera gets "self-stabilized" by gravity. However, consider now the gimbal being accelerated to the right. Because the center of gravity is below the pitch axis, where would be a force on the camera and it would tilt downwards. The PID controller would have to fight against that, which makes it much harder or even impossible for it to stabilize the camera.		The picture below shows a badly balanced situation. The center of gravity is quite below the pitch motor axis. At first this might actually look like a good idea, since the camera gets "self-stabilized" by gravity. However, consider now the gimbal being accelerated to the right. Because the center of gravity is below the pitch axis, where would be a force on the camera and it would tilt downwards. The PID controller would have to fight against that, which makes it much harder or even impossible for it to stabilize the camera.

	The video shows a well balanced gimbal. Here it is possible to move the camera to any orientation and let it free, without it turning back to a ~~prefered~~ orientation.		The video shows a well balanced gimbal. Here it is possible to move the camera to any orientation and let it free, without it turning back to a preferred orientation.

	Some further tips:		Some further tips:
	* It is better to physically disconnect the motors from the board, since then they can move more freely than just ~~beeing~~ disabled in the GUI.		* It is better to physically disconnect the motors from the board, since then they can move more freely than just being disabled in the GUI.
	* A more severe test to check balance is to heavily shake the gimbal, up and down, left and right, forward and backward. When balanced, the camera will stay in the position it was before the shaking started. Do this for different camera positions.		* A more severe test to check balance is to heavily shake the gimbal, up and down, left and right, forward and backward. When balanced, the camera will stay in the position it was before the shaking started. Do this for different camera positions.
	* A 3-axis gimbal requires more precise balancing than a 2-axis gimbal. Especially the yaw axis needs attention.		* A 3-axis gimbal requires more precise balancing than a 2-axis gimbal. Especially the yaw axis needs attention.
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	An example tuning is illustrate in the video. Listen to it (switch on audio). Initially D = 0.17, and the gimbal is shaking like mad, with low frequency and high amplitudes. Then the value is reduced to D = 0.10, and the camera position becomes stable, but a high-frequency noise can clearly be heard. With D = 0.05 the frequency gets even higher. We want the frequency to be that high that no noise is audible. At D = 0.04 the noise is suddenly gone.		An example tuning is illustrate in the video. Listen to it (switch on audio). Initially D = 0.17, and the gimbal is shaking like mad, with low frequency and high amplitudes. Then the value is reduced to D = 0.10, and the camera position becomes stable, but a high-frequency noise can clearly be heard. With D = 0.05 the frequency gets even higher. We want the frequency to be that high that no noise is audible. At D = 0.04 the noise is suddenly gone.

	Before the video was taken, the following actually ~~happend~~. First D = 0.04 was picked, and everything was fine. With increasing it to 0.05, everything was still fine. At D = 0.06 heavy vibrations were visible, hence the previous D = 0.05 value was set, but now vibrations were still present! In this situation one could manually move the motor into a different position and the vibrations would go away. What happened? At D = 0.06 the resonance frequency of the control loop was hit, but with a slight decrease to 0.05 the frequency remained very similar and the control loop was not able to get out of it by itself. So, to be on the safe side D = 0.04 was ~~choosen~~, as for this value the shaking stopped by itself. The message is that it's quite natural to observe a hysteresis, that is that when coming from large D values one needs to go to smaller D values to stop a vibration than the other way around. Choose the smaller D value, at which the vibrations stop.		Before the video was taken, the following actually happened. First D = 0.04 was picked, and everything was fine. With increasing it to 0.05, everything was still fine. At D = 0.06 heavy vibrations were visible, hence the previous D = 0.05 value was set, but now vibrations were still present! In this situation one could manually move the motor into a different position and the vibrations would go away. What happened? At D = 0.06 the resonance frequency of the control loop was hit, but with a slight decrease to 0.05 the frequency remained very similar and the control loop was not able to get out of it by itself. So, to be on the safe side D = 0.04 was chosen, as for this value the shaking stopped by itself. The message is that it's quite natural to observe a hysteresis, that is that when coming from large D values one needs to go to smaller D values to stop a vibration than the other way around. Choose the smaller D value, at which the vibrations stop.

	{{COMMENT\|In the GUI you can move the slider also using the cursor keys. Click on the slider handle with the mouse, and hit the left/right key to change the value by its minimal step width. Very useful, especially for adjusting D.}}		{{COMMENT\|In the GUI you can move the slider also using the cursor keys. Click on the slider handle with the mouse, and hit the left/right key to change the value by its minimal step width. Very useful, especially for adjusting D.}}

OlliW: /* The Starting Point */

2015-01-10T14:08:52Z

The Starting Point

← Older revision		Revision as of 16:08, 10 January 2015
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	* All three axes should be in hold mode, i.e., in the {{GUI\|Pan}} tab the parameters {{PARAMNAME\|Pitch Pan}}, {{PARAMNAME\|Roll Pan}} and {{PARAMNAME\|Yaw Pan}} should be set to zero or alternatively the {{PARAMNAME\|Pan Mode Default Setting}} set to {{PARAMVALUE\|hold hold hold}}.		* All three axes should be in hold mode, i.e., in the {{GUI\|Pan}} tab the parameters {{PARAMNAME\|Pitch Pan}}, {{PARAMNAME\|Roll Pan}} and {{PARAMNAME\|Yaw Pan}} should be set to zero or alternatively the {{PARAMNAME\|Pan Mode Default Setting}} set to {{PARAMVALUE\|hold hold hold}}.
	* {{PARAMNAME\|Voltage Correction}} should be set to 0%.		* {{PARAMNAME\|Voltage Correction}} should be set to 0%.
			* A 2nd IMU should be deactivated, i.e., in the {{GUI\|Setup}} tab the parameter {{PARAMNAME\|Imu2 Configuration}} should be set to {{PARAMVALUE\|off}}.
	* The battery should neither be fully charged nor nearly discharged, i.e., have a voltage of about 3.7 V per cell.		* The battery should neither be fully charged nor nearly discharged, i.e., have a voltage of about 3.7 V per cell.

OlliW at 10:41, 10 January 2015

2015-01-10T10:41:52Z

← Older revision		Revision as of 12:41, 10 January 2015
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	See [http://en.wikipedia.org/wiki/PID_controller Wikipedia] for further details on PID control.		See [http://en.wikipedia.org/wiki/PID_controller Wikipedia] for further details on PID control.

	Below a relatively simple and straight forward tuning technique is suggested, which often works surprisingly well, and has a ~~solid~~ theoretical foundation. However, it may also fail. In fact, it is important to realize that some gimbals might not be tunable at all, because e.g. too weak or too strong motors are used, and other reasons. As a rule of thumb: When you don't get a good tuning within 10 min (per axis) then chances are that something is wrong with the gimbal design. There ain't no such thing as a hard to tune gimbal. There are just well and badly designed gimbals.		Below a relatively simple and straight forward tuning technique is suggested, which often works surprisingly well, and has a theoretical foundation. However, it may also fail. In fact, it is important to realize that some gimbals might not be tunable at all, because e.g. too weak or too strong motors are used, and other reasons. As a rule of thumb: When you don't get a good tuning within 10 min (per axis) then chances are that something is wrong with the gimbal design. There ain't no such thing as a hard to tune gimbal. There are just well and badly designed gimbals.

	== Balancing the Gimbal ==		== Balancing the Gimbal ==

OlliW: /* The I Parameter */

2015-01-10T10:41:24Z

The I Parameter

← Older revision		Revision as of 12:41, 10 January 2015
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	=== The I Parameter ===		=== The I Parameter ===

	Now ~~we want to set~~ {{~~GUI~~\|I}} to the ~~maximum~~ value ~~possible~~ without introducing ~~any~~ side effects. If you look carefully at the last few seconds of the previous video, when {{GUI\|I}} was at 5 still, the camera could not be kept level when the gimbal itself was moved. The {{GUI\|I}}ntegral term (integral over the time) is responsible for this part of the movement.		Now the {{PARAMNAME\|I}}ntegral term can be adjusted. The goal is, similar to the other parameters, to find the largest possible value without introducing negative side effects.

	In the video ~~below~~ the {{~~GUI~~\|I}} value is ~~increased~~ to 480 ~~initially and~~ in comparison ~~you can see~~ the ~~same movement with~~ I = 5~~. Perfect~~ movement now, fast speed, the camera remains horizontal, it truly is horizontal, everything fine. ~~But maybe we~~ can increase it even further. At 700 the same situation, everything looks nice. ~~But at~~ I = 1200 ~~you can see that~~ the camera ~~no longer is~~ horizontally aligned, ~~the "time" aspect of the control loop starts to overcompensate. If~~ you look carefully at the yellow cable of the IMU connector, it is vibrating - sorry, not very visible in the video. So 1200 is a too high ~~value~~ for sure. There were slight vibrations in some positions of the camera at 700 ~~even~~, so {{~~GUI~~\|I}} ~~got~~ set to 620 at the end.		In fact, the {{PARAMNAME\|I}} term plays a much more important role for the stabilization accuracy than the {{PARAMNAME\|D}} and {{PARAMNAME\|P}} parameters. In practical terms this means, that it is more important to set a large {{PARAMNAME\|I}} value, or vice versa, that one doesn't loose too much if {{PARAMNAME\|D}} and {{PARAMNAME\|P}} are not at their highest possible values. So, it is actually not a bad idea to lower {{PARAMNAME\|D}} and {{PARAMNAME\|P}}, as this increases e.g. the reliability of the PID controller behavior.

			When you look carefully again at the last few seconds of the previous video, where {{PARAMNAME\|I}} was 5, you'll see that the camera could not be kept level when the gimbal was moved. The {{PARAMNAME\|I}} term is responsible for this part of the movement.

			In the video, the {{PARAMNAME\|I}} value is initially set to 480. I in comparison to the behavior for I = 5, a perfect movement is now obtained: fast speed, the camera remains horizontal, it truly is horizontal, everything is fine. Maybe one can increase {{PARAMNAME\|I}} even further. At I = 700 the same situation, everything looks nice. At I = 1200, however, the camera isn't horizontally aligned, and - if you look carefully at the yellow cable of the IMU connector - you see that it is vibrating (sorry, not very visible in the video). So, I = 1200 is too high for sure. There were slight vibrations in some positions of the camera even at I = 700, so {{PARAMNAME\|I}} was set to 620 at the end.

	{{#ev:youtube\|kGFhd7Q4vgw}}		{{#ev:youtube\|kGFhd7Q4vgw}}

OlliW at 10:20, 10 January 2015

2015-01-10T10:20:53Z

← Older revision		Revision as of 12:20, 10 January 2015
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	The video shows the procedure. After five seconds, {{PARAMNAME\|P}} and {{PARAMNAME\|I}} are set to non-zero values and the gimbal moves into a level position. Then the {{PARAMNAME\|P}} value is increased. Once P = 15 is reached, some weird shakes start to appear when the motor is released from a tilted position, which get worse and worse, and with P = 23 the camera shakes for a while even. Only once the {{PARAMNAME\|P}} value is set back to 13 a smooth movement from all positions is achieved again.		The video shows the procedure. After five seconds, {{PARAMNAME\|P}} and {{PARAMNAME\|I}} are set to non-zero values and the gimbal moves into a level position. Then the {{PARAMNAME\|P}} value is increased. Once P = 15 is reached, some weird shakes start to appear when the motor is released from a tilted position, which get worse and worse, and with P = 23 the camera shakes for a while even. Only once the {{PARAMNAME\|P}} value is set back to 13 a smooth movement from all positions is achieved again.

	{{#ev:youtube\|O_FC6S_Lpgs}		{{#ev:youtube\|O_FC6S_Lpgs}}

	=== The I Parameter ===		=== The I Parameter ===

← Older revision		Revision as of 12:41, 10 January 2015
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	=== The I Parameter ===		=== The I Parameter ===

	Now ~~we want to set~~ {{~~GUI~~\|I}} to the ~~maximum~~ value ~~possible~~ without introducing ~~any~~ side effects. If you look carefully at the last few seconds of the previous video, when {{GUI\|I}} was at 5 still, the camera could not be kept level when the gimbal itself was moved. The {{GUI\|I}}ntegral term (integral over the time) is responsible for this part of the movement.		Now the {{PARAMNAME\|I}}ntegral term can be adjusted. The goal is, similar to the other parameters, to find the largest possible value without introducing negative side effects.

	In the video ~~below~~ the {{~~GUI~~\|I}} value is ~~increased~~ to 480 ~~initially and~~ in comparison ~~you can see~~ the ~~same movement with~~ I = 5~~. Perfect~~ movement now, fast speed, the camera remains horizontal, it truly is horizontal, everything fine. ~~But maybe we~~ can increase it even further. At 700 the same situation, everything looks nice. ~~But at~~ I = 1200 ~~you can see that~~ the camera ~~no longer is~~ horizontally aligned, ~~the "time" aspect of the control loop starts to overcompensate. If~~ you look carefully at the yellow cable of the IMU connector, it is vibrating - sorry, not very visible in the video. So 1200 is a too high ~~value~~ for sure. There were slight vibrations in some positions of the camera at 700 ~~even~~, so {{~~GUI~~\|I}} ~~got~~ set to 620 at the end.		In fact, the {{PARAMNAME\|I}} term plays a much more important role for the stabilization accuracy than the {{PARAMNAME\|D}} and {{PARAMNAME\|P}} parameters. In practical terms this means, that it is more important to set a large {{PARAMNAME\|I}} value, or vice versa, that one doesn't loose too much if {{PARAMNAME\|D}} and {{PARAMNAME\|P}} are not at their highest possible values. So, it is actually not a bad idea to lower {{PARAMNAME\|D}} and {{PARAMNAME\|P}}, as this increases e.g. the reliability of the PID controller behavior.

			When you look carefully again at the last few seconds of the previous video, where {{PARAMNAME\|I}} was 5, you'll see that the camera could not be kept level when the gimbal was moved. The {{PARAMNAME\|I}} term is responsible for this part of the movement.

			In the video, the {{PARAMNAME\|I}} value is initially set to 480. I in comparison to the behavior for I = 5, a perfect movement is now obtained: fast speed, the camera remains horizontal, it truly is horizontal, everything is fine. Maybe one can increase {{PARAMNAME\|I}} even further. At I = 700 the same situation, everything looks nice. At I = 1200, however, the camera isn't horizontally aligned, and - if you look carefully at the yellow cable of the IMU connector - you see that it is vibrating (sorry, not very visible in the video). So, I = 1200 is too high for sure. There were slight vibrations in some positions of the camera even at I = 700, so {{PARAMNAME\|I}} was set to 620 at the end.

	{{#ev:youtube\|kGFhd7Q4vgw}}		{{#ev:youtube\|kGFhd7Q4vgw}}