Dear Friends,
after one week of work to first sample of electronics , we are ready with workspace enviroment for developer that want join our team.
Electronic Specification:
In VR Gimbal We decide to use this kind of electronic parts :
- as micro we use STM32F1 64 pin.
- 1 MPU6000 + HMC5883 for Z axis Direct Drive CAM using i2c bus.
- 1 MPU6000 on spi bus. for Roll and Pitch cam.
- EEPROM for storage the parameter of gimbal.
- 3 ST Driver for manage 3 Brushless Motors with 9 Hardware PWM Output.
- 1 input for Ublox GPS.
- 4 PPM Radio Input or 1 PPMSUM radio input until 8 channel or more.
- 1 Telemetry port for mavlink control.
As developer enviroment we use VR Ide Universal (based on eclipse) compatible with VRBRAIN and MP32 board now also with VR GIMBAL.
The developer lib and hal at the begin will be compatible with our APM_LIB ported to STM32F1 library the same used on MP32F1 board.
That support all the APM library available and arduino language sintax .
In our code we decide to port on VR Gimbal :
- AP_COMMON
- AP_VAR
- AP_InertialSensor
- AP_IMU
- AP_Camera
- AP_Mount
- Mavlink
and other utility yet available on our standard F1 package ...
We would develop also a utility for manage the board on pc and on android smartphone.
If you are interest to join our work in developing stage will be a special price for you of 75 euro for 3 axis control board + 15 euro for IMU (at the moment is available only 20 board) .
Your name will be in the list of developer of this project. The code will be opensource as other in this great community ... the support in development and donation are welcome .
For more info about the project contact me at info@virtualrobotix.com
In our roadmap the first stable version of code will be available in 1 month.
In the next week will be available the enviroment , with hal and library , then starting to implement the code functionality for manage the first opensource 32 bit 3 axis direct drive.
I hope that you like our project and join us in development.
In VR Lab mecatronix group are working hard and is yet available a good gimbal for GOPRO
And also is coming Gimbal for pro and semi pro camera.
I hope that you like our work :)
for more info and join us : http://www.virtualrobotix.com/group/vr-gimbal-user-group?xg_source=activity
Best
Roberto Navoni
Comments
After thinking about the problem, the Z axis IMU is what you want. The relative roll/pitch of the 2 IMU's determines how much yaw is contributing to roll/pitch. It would take fusing the 2 IMU's to determine all the feedback of the motors.
ERRATUM: your gimbal is PITCH last, so inverse roll and pitch in my comments
Yes, I think so... It will be possible with 2 potentiometers on 2 first axis Yaw and Pitch (but it's additionnal friction, and not easy to adapt). Other existing solutions are expensive (this is what Zenmuse does at a very competitive price).
No problem on the last Roll axis : a simple PID could be enough.
SPI on a long wire could become another headake, no ?
Hi Stephane ,
you can use a special motor with potentiometer with inverse kinematic approach and use only 2 imu ?
If need 3 imu i can use 2 spi module and 1 i2c , it's not a problem the hardware support this configuration.
It's only a bit more expensive :)
Best
Roberto
I'm sorry Roberto, but with 1 IMU on camera, and 1 IMU (or AHRS) on main board, it's impossible.
Actual 2 axis gimbal uses PID to control attitude, because you know that a "pitch action" will act on the "pitch axis only".
But on a 3 axis system, if you don't know absolute angular position of each of the 2 first axis, it's just impossible to do with a PID blind control loop, because a PID can't resolve a matrix problem...
Hi Stephane,
i' understand your point of view but i think that for entry level solution 1 imu is ok . If you need z axis you can have second imu with magnetometer ... now i check if is possible to add another imu ... i can use SPI bus and on it i can have a lot on imu :) need to put only 1 chipselect for each one.
About the micro controller at the moment my entry level Control Board use STM32F1 at 72 mhz without internal dsp but i have a lot of experience on stm32F4 that is the micro used on VRBRAIN our Copter and Plane flight control so is not a problem use that micro instead of F1 in an PRO version .
I use F1 instead of F4 because i don't found a stm32f4 64 pin micro controller i need to check for F3 ... but is not powerfull as F4.
Best
Roberto
It's too bad Roberto, as Jack said, I'm afraid it won't work, even with 1 IMU for each axis, because you'll ever get some misalignment between the 3 attitudes estimation. Even with a very accurate initialization position + the best Kalman + fine calibrated Gyro and Accel, there could be 2-5° error for each axis. That kind of result with 2 downstream levels would be dramatic on final video result.
Of course you can imagine a very clever system with 3 AHRS (magneto will be necessary), that can learn by itself :
- absolute angular position of each motor at initialization (not too difficult if the all gimbal stays still in that step).
- the angular error accumulated on each motor in operation (it's nearly impossible to get a good prediction model without direct measurements)
I don't know if it is so easy... What about gimbal lock situation too for that extra maths ?
Even with that complex maths, I believe you'll get a lot of combined little bias sources difficult to deal with. It stills possible in theory: but to compete with Zenmuse, this extra maths will have to be computed at very, very high frequency on a very powerfull chip like the STM32F4 for example (but would it be enough ?)...
3xKalman (1 fo each AHRS)
+ 1xLevenberg Marquardt on 4(quaternion)x2(misalignement levels)= 8dof (that's a lot of compute)
+ 1 optional simple Kalman level to smooth levenberg marq output that would be noisy
@t 500Hz for example, if you don't want to accumulate some visible errors.
That's a lot of fun in maths... Ask Bill perhaps ??
Good luck ;)
Hi Roberto,
I would be happy to have a look at the control algorithms and data conditioning stuff.
Nice work!
@Jack,
HI Jack , you have a lot of experience in 32bit development , your suggestions are welcome . About the potentiometer we have on VR Gimbal DDC 6 analog input for put more sensor on motors if it is need in future development. Why you think that we need 3 imu one for each axis ? Is not enought 2 one on camera and other on 3°th axis for yaw control and gps stabilization ?
Best
Roberto
Hi Kraut,
i hope no ,too :) I think that our board could be the next step in this kind of application , it will be opensource , based on APM library so there is a big opportunity for our developer to implement a lot of new feature ; Alexmos isn't opensource. it's a good rtf product :)
I have a lot of possible application for this kind of board in my mind, not only for gimbal on drone :)
So if someone like to join in development is welcome :)
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