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Sep 10, 2014, 01:28 AM
LeViteZer smooths the movement
GARUG's Avatar
Mini-HowTo

Referencing gimbal Yaw to airframe


This Mini-HowTo is about how to use follow mode with 3 axis gimbals on airborne applications, so that the average heading of the gimbal is fixed to forward related to airframe.

Using Gimbal Follow Yaw is good for filtering out any sudden Yaw movements, but the general problem is that gyros drift and if the gimbal is disturbed by airflow etc. it can loose orientation. The solution is to add an absolute reference for the gimbal that tells all the time for the gimbal controller where the airframe is heading.

This is very useful on installations where the Gimbal Yaw movement is limited, like in this installation, where the 3 axis gimbal is between front propellers. (see the shadow at 0:40)


Calm Down edited2 (1 min 46 sec)


The solution is really easy and probably works with any gimbal controller that supports analog joystick. I am using BaseCam 32bit board.

First a 2to 10 kohm linear potentiometer needs to be connected so that it detects the gimbal yaw movement related to airframe. i.e. one end of the potentiometer connected to airframe (damper plate), other end to the gimbal Yaw axis.

The potentiometer should be installed so that it is at its middle of the travel when the gimbal is pointing directly front. There should be possibility to adjust the potentiometer so that the direction can be later on fine-tuned.

The potentiometer is electrically connected to the controller as analog Yaw joystick would be connected. Refer to the instructions of your board.

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Edit March, 20 2016: BaseCam latest FW 2.55b8 (beta) and upward now support follow encoder with PWM and I2C interface. http://forum.basecamelectronics.com/...r-alone#Item_3
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The next step is adjusting the board parameters for the Yaw joystick control. Set it to work on Speed mode. The movement direction needs to be set so that the gimbal tries always to centre itself. Adjust the potentiometer mechanically so that the gimbal points directly ahead.

When the gimbal is centring it self, the speed, dead band, expo, LPF etc. are used to tune the Yaw follow. It is also possible to use the controllers Follow mode in combination, but I have found it better to use without the actual Follow mode activated.

The LeViteZer gimbal I am developing is a prototype and I can not post pictures of it yet, but please post pictures of your installations and settings that you are using to support others.

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LeViteZer smooths the movement, www.levitezer.com
Last edited by GARUG; Mar 20, 2016 at 02:36 AM.
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Sep 10, 2014, 09:57 AM
Registered User
HummingbirdRPV's Avatar
Sounds like a feasible idea, I'll have to give it a try.
Sep 10, 2014, 11:01 AM
Gary
glmccready's Avatar
Thanks for the more detailed explanation.
Sep 12, 2014, 05:34 AM
Registered User
Do you have a photo of your setup?
Sep 12, 2014, 05:40 AM
LeViteZer smooths the movement
GARUG's Avatar
yes, but as I mentioned "The LeViteZer gimbal I am developing is a prototype and I can not post pictures of it yet"

The principle is really simple though, just connect the potentiometer as described above.

Quote:
Originally Posted by fjj1
Do you have a photo of your setup?
Sep 13, 2014, 02:47 PM
LeViteZer smooths the movement
GARUG's Avatar
To clarify. For this to work the potentiometer axis needs to rotate when gimbal yaw axis rotates. Hopefully the attached picture clarifies this.
Sep 13, 2014, 06:41 PM
Gary
glmccready's Avatar
Well then the kind I bought won't work. The one I got is just to adjust the pot on the Alexmos. You actually connect the pot to the motor, and case to the frame.
Sep 14, 2014, 02:29 AM
LeViteZer smooths the movement
GARUG's Avatar
The principle of operation is that when the gimbal yaw turns from the directly ahead position, it turns the Yaw potentiometer that causes the gimbal to center again. The Yaw potentiometer sends a proportional speed signal depending how much the gimbal yaw is deviated.

Yaw RC ‘deadband around center’ is set so that the Yaw may move some degrees without any corrections. This smooth’s out any small deviations. RC Expo curve and speed are used so that Yaw follows smooth.

So yes, it is absolutely necessary that the potentiometer is mechanically connected so that it turns when gimbal yaw rotates.
Sep 14, 2014, 04:35 AM
LeViteZer smooths the movement
GARUG's Avatar
Here is couple of pictures how the yaw potentiometer is set up on GUI.

Ps. as I mentioned here https://www.rcgroups.com/forums/show...postcount=1137

"There is nothing new on this solution, just that I have not seen it to be used with brushless gimbals."
Sep 14, 2014, 04:56 AM
LeViteZer smooths the movement
GARUG's Avatar
Connecting the potentiometer can be a bit tricky, but for it to work, it does not need to be anything fancy, I installed it with the Blutack for the first trials on the prototype :-)

Hollow saft helps the installation The axis of the potentiometer is attached to the other end of the motor and the potentiometer shell with Blutack to the other end. Blutack makes it easy to adjust.

For next version for sure the installation will be improved.
Sep 14, 2014, 10:20 AM
Registered User
Hi,

I've just swapped out the 8 bit board from my DYS 3 axis Gopro gimbal and discovered this unfortunate yaw issue, see here:
Alexmos basecam 32 bit controller poor yaw (and roll) stability (5 min 47 sec)


Excuse the quality but I rendered it at 720p just to show the issue and it was nearly dark..

I have realised that I made a mistake by mounting the frame IMU on the non-dampened frame so it was separated by the rubber mounts from the camera IMU so I've moved that so hopefully that might help some generally but I don't expect it will help the yaw problem.

I'm sorry if this has been mentioned elsewhere but why does the 8 bit board keep the yaw axis central whereas the 32 bit board won't? What's different?

Is this likely to be resolved with a firmware update as if not, I shall be sending the 32 bit board back as it's unusable..

Thanks,

Peter.
Sep 14, 2014, 10:36 AM
LeViteZer smooths the movement
GARUG's Avatar
I am using Follow Yaw with normal 2 IMU 32 bit setup on handheld and it works just great.

The reason I use potentiometer on arial platform is that I want to remove any problems getting the heading right when the system is started, remove drifting problems, because the gimbal must stay between +-30 degrees yaw (between propellers).

I have not really used normal Follow yaw on aerial gimbals (8 bit or 32 bit) but I am surprised if 32 bit performs worse. On handheld it performs very well.

Maybe you could try to get the 32 bit working first with 1 IMU.
Sep 14, 2014, 11:21 AM
Gary
glmccready's Avatar
GARUG: Thanks!
I have a 5k Ohm poti with a knob, but need to figure out how to mount it, since I have a slip ring with wires going through it, on my Yaw. I'm thinking on the side with a belt. I did hook up the Poti but couldn't get it to center. I'll try again with your settings.
Sep 14, 2014, 01:19 PM
LeViteZer smooths the movement
GARUG's Avatar
The potentiometer is really only suitable for installations that have limited yaw movement (as the potentiometer range is limited), so you do not really need slip ring on yaw.

Quote:
Originally Posted by glmccready
GARUG: Thanks!
I have a 5k Ohm poti with a knob, but need to figure out how to mount it, since I have a slip ring with wires going through it, on my Yaw. I'm thinking on the side with a belt. I did hook up the Poti but couldn't get it to center. I'll try again with your settings.
Last edited by GARUG; Sep 14, 2014 at 01:32 PM.
Sep 14, 2014, 01:24 PM
Registered User
Quote:
Originally Posted by GARUG
I am using Follow Yaw with normal 2 IMU 32 bit setup on handheld and it works just great.

The reason I use potentiometer on arial platform is that I want to remove any problems getting the heading right when the system is started, remove drifting problems, because the gimbal must stay between +-30 degrees yaw (between propellers).

I have not really used normal Follow yaw on aerial gimbals (8 bit or 32 bit) but I am surprised if 32 bit performs worse. On handheld it performs very well.

Maybe you could try to get the 32 bit working first with 1 IMU.
Thanks Garug.

The 32 bit board works fine for a while then drifts whereas the 8 bit board kept central to the frame all of the time unless I fly the Spy hard when it would occasionally slip round to the next magnet. Will try the one IMU approach although I've shortened all the cables to save a little weight and for tidiness so that may prove a little problematic.

Am just going out for a few flights, will see how the new frame IMU position affects things..


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