First Flight - SteadiDrone QU4D Brushless Gimbal from SteadiDrone on Vimeo.

As you all know brushless gimbals are the future, and we've just tested our first small BG for our SteadiDrone QU4D, here are some quick clips, much more to come soon. You can check out our facebook pages for more news, photos, videos etc

https://www.facebook.com/SteadiDrone

https://www.facebook.com/groups/283605021770387/

Regarding ArduCopter and brushless gimbals, would it be possible to impliment a AlexMos type code so that the code/APM can control brushless gimbal motors ??? mmmmmm would be a dream if we could

 

 

SteadiDrone QU4D Brushless gimbal prototype testing from SteadiDrone on Vimeo.

Views: 4208

Tags: brushless, copter, diy, drone, drones, gimbal, gopro, qu4d, quad, steadidrone


Developer
Comment by Rob_Lefebvre on April 10, 2013 at 7:12am

Yeah, I thought it was supposed to be about to do that 9 minutes after taking it out of the box? ;)

Comment by Duran - SteadiDrone on April 10, 2013 at 7:19am

;) lol. Right now, after doing everying Collin said it does GPS hold, it actually will stay in the same town, more or less.

Comment by Duran - SteadiDrone on April 10, 2013 at 7:19am

make that the same zip code.

Comment by thomas Butler on April 10, 2013 at 8:02am

The AlexMos gimbal controller is in effect a three phase stepper motor control.  The "rewinding" increases the resistance of the windings so they can become electro magnets and don't fry.  The stepper controller chip sequences on/off to the windings to cause CW or CCW rotation.  The same end result can be accomplished with a standard stepper motor (which is two phase) and a stepper control chip.  The chip takes CW/CCW pulses and ramps up and down the RPM of the motor.  The down side is a standard stepper motor is wired in series with a resistor to dump current; ie. waste power. A uP can control the driver transisitors directly, but it must do the phase sequencing and ramping in real-time.  A stepper control chip and the AlexMos control do the sequencing; offloading that real-time task from the flight controller.  Stepper motors with sufficient torque and horsepower would be a bit heavier than a rewound BLDC motor.  The tradeoff is that the AlexMos contoller using a rewound BLDC motor is much more power efficient and less weight.

It's a good idea AlexMos code in no longer open source.  That means all and any bugs are his responsibility, but like everything else, it's not hard to write the sequencing code and burn it into one's own uP, but it's a whole lot easier to spend $80 and buy a working AlexMos device!  Why reinvent the wheel?  I'll but one after the first few versions shake out the bugs or issues.

http://web.inter.nl.net/users/Ussel-IntDev/fischertechnik_public/mi...

http://www.ti.com/lit/an/slva416/slva416.pdf

http://www.stepperworld.com/Tutorials/pgMicrostepping.htm

http://www.st.com/web/catalog/sense_power/FM142/CL851/SC1794/SS1498...

 

 


Developer
Comment by Randy on April 10, 2013 at 8:15am

thomas,

    nice info.  i've been following this thread in the hopes of a post like that. txs!

Comment by Joshua Ott on April 10, 2013 at 9:41am

What about manual override control of tilt axis? Does the AlexMos controller have a provision for this?


Developer
Comment by Rob_Lefebvre on April 10, 2013 at 10:12am

Joshua, what do you mean exactly?

The controller takes a standard PWM servo input.  You set it up so that, for example, 1100 PWM means "point straight down" and 1900 PWM means "point straight ahead".  And then it does the rest from there.  Whatever the body-frame of the copter does, it compensates, so that it is pointing at the desired earth-frame angle. 

Currently, the mount code of the APM attempts to do the body-frame correction, because it is supposedly outputting to a dumb servo.  

So in fact, all that we need to do to the APM to get it to drive an AlexMos board, is to remove the earth-frame correction.  When you set a ROI, it should calculate the declination or azimuth, and just send that out as a servo signal, with NO body-frame stabilization.  Simple as that.  So we actually only need to simplify the Mount code to drive an AlexMos board.

There is a difference between stepper motors, and BLDC motors, that is very important.  Stepper motors tend to be single phase or two phase.  This means that typically, they move in discrete steps.  Commonly just under 1° per step.  This is far too coarse for a camera gimbal.  There's stuff you can do like micro-stepping, but I'm not entirely sure what that means.

BDLC motors are 3-phase.  What Zenmuse (and thus AlexMos) are doing is using a 3-phase bridge, PWM control, to produce an infinitely variable magnetic angle inside the motor!  There are no discrete steps.  This is the key to the success of these.  They produce a stationary magnetic field in the motor, and the rotor aligns itself to this.  This is why the movement is so smooth.  

But, the downside is that I believe this system has much lower torque than a stepper motor (or a servo).  That is why balance of the gimbal is absolutely critical.  They don't really have much torque to move the camera.  The camera is actually stationary, the copter rotates around it, and the BLDC motor is really only overcoming the friction in the bearings.

Comment by Joshua Ott on April 10, 2013 at 5:31pm

Thanks Robert,

I was under the impression that it only kept the camera level and had no possibility for the APM to pass through manual inputs from the user or a "point camera on target function". Sounds like that's not a problem!

Comment by Duran - SteadiDrone on April 11, 2013 at 12:19pm

Joshua, the controller supports full tilt and roll control as well as the channels to get info or control from flight controller too!

Comment by LanMark on April 11, 2013 at 12:30pm

does it support a 230g point and shoot camera like a Canon ELPH? :) 

(I figure if I keep asking someone would stop making GoPro specific stuff and open the doors to many more customers that personally don't like GoPro, especially in the image distortion department)

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