Gimbals/Electronics from FPV Remote Control

edited April 2013 in KAP Gear Sources
I didn't see any mention of it here yet, and I'm sure many of you are already aware, but there are a number of sources of gimbals and electronics coming onto the market that would be easily adapted to KAP from the FPV/AP (First Person Video/Aerial Photography) crowd. Many of them are focused on the GoPro size cameras, but there are also DSLR sizes.

For are some examples: (Gimbals)

Go Pro Size:
http://www.rctimer.com/index.php?gOo=goods_details.dwt&goodsid=872&productname=


DSLR:

http://www.rctimer.com/index.php?gOo=goods_details.dwt&goodsid=885&productname=

Electronics:

Control boards such as these 3 axis accelerometers and 3-axis gyros, and firmware that already supports self leveling.

http://www.hobbyking.com/hobbyking/store/__24723__Hobbyking_KK2_0_Multi_rotor_LCD_Flight_Control_Board.html

There are many other varieties of these boards.

Of course, you could also just use 2 or 3 of Scott's excellent GS-1's....


Matt

Comments

  • this is definitely my next project, it looks like all our problems will be solved.

    this is also a nice site with lots of components: http://www.tarot-rc.com

    the only downside is the weight of a brushless gimbal rig. but this is the way to go.

    My project will be called 'GimRig' and I'll write about the progress on http://www.lightcatcher.nl

    cheers
    emiel
  • @emiel, I checked your webpage, nice. When I made my auto/RC KAP rig I used a Pololu servo multiplexer.

    http://www.pololu.com/catalog/product/721

    Mike
  • One issue with these is that the control system designers probably assume that the inertia of the thing they are mounted on is fairly high, on par or more than the camera. On a typical kite system, there's not much there. Put another way, there's not much to push against to spin the camera. I ran into this for my high altitude balloon project and ended up making the puffer system. Not a practical suggestion!
    Anyway, I think mounting a DSLR on a Picavet might be a bad idea for this reason. I think stability (in the control system sense) might be difficult to attain. It may have severe overshoot or ringing or maybe even oscillate. This will depend on how fast the control loop is. It may have to be delibrately slowed down too much to be much use.
    I think emiel's suggestion of getting rid of the Picavet is a good one. I think using the taught kite line to torque against might be important, either directly (better) or with a pendulum.

  • That puffer system is cool! It's not too far off from the attitude rockets used on spacecraft. Another possibility is something Scott Armiatge used a while ago on his single string suspension KAP rigs: a moving reaction mass (in his case a reaction mass with paddle wheels so you can use the air as mass as well). Speed it up, and you induce a rotation in one direction. Slow it down or reverse it, you induce rotation in the other direction. This is fairly close to how spacecraft like HST point.

    I'm glad this topic is getting some attention. I think there's a ton of progress to be made along these lines. But I don't think it's as straightforward as taking an off-the-shelf gimbal and hanging it from a KAP suspension. Every time I've tried to do that, something winds up being funky. Take a look at any of the threads discussing Servo City hardware for examples. If it's not a weight issue, it's a balance issue. If not balance, it's battery drain. If not that, cost. It goes in circles.

    But I LOVE looking at a design and pulling ideas from it. I've been trying to find a good direct-drive axis motor and controller for a while. This is AWESOME! $50 for the controller/IMU, and $18 per axis for the direct-drive motors. With careful construction, the gimbal itself can be built from Brooxes hardware and be just as light and balanced as any other KAP rig. I've been using Hitec HS-645MG servos on my DSLR rig. The cost of a rig built with two of those versus the direct-drive approach is almost identical.

    Hang this from a damped pendulum that has a good long arm on the kite line, pivots with no side-play (double-row ball bearings or cross-roller bearings), and is built from materials that don't allow for much flex or twist, and you may very well have a KAP rig that spells the end to the wobblies.

    Tom
  • Sorry for the double-post, but I've been doing some thinking and reading since replying this morning.

    Brushless direct-drive gimbals are a hot-bed of development right now. The ones on the market at the moment are 2-axis controllers, but a 3-axis controller is under development and should be released soon. Prototypes have already been built.

    The motors must be wound specifically for this application. Right now there are only a handful of motors that are being offered as off-the-shelf parts, but enthusiasts are winding all kinds of different setups for different sized cameras. It reminds me of when brushless DC motors first hit the RC market. People were gutting BLDC motors out of CDROM drives and re-winding them to drive propellers instead. I don't think it'll be long before the physics is better understood, and motors are specifically designed for use as gimbal motors.

    There are some tricks with using these things that actually lend themselves better to KAP than to the original design purpose: RC helicopters and multirotors. One of the biggest bugaboos with prop-driven RC aircraft is vibration. No matter how much the motors and props are balanced, the vibration will still be there. Vibration is the enemy of the IMU used on these things. To combat it, anti-vibration mounts for the gimbal are used, and the IMU is often mounted on foam tape. The problem is that even the lag induced by mounting the IMU on foam tape is enough to throw the system off. But KAP doesn't suffer from the high frequency vibrations that cause these issues on RC aircraft. If anything, a KAP suspension should be easier to mount a brushless gimbal to, and should perform better.

    I think a careful combination of suspension and gimbal design will result in a wobble-free KAP rig. I'm going to continue the experiments I've been doing with damped pendulums. But I'm waiting for the 3-axis brushless gimbal controller before I take the plunge into a brushless camera gimbal. I think it'll work in the end, though.

    Tom
  • @emiel - your site appears to be down right now, but I'll be watching progress!

    @bededict/Tom - I think you're right, although I'm not sure that active adjustment is required on all 3 dimensions, given that the yaw dimension can be fairly easily controlled by the kite line, which is fairly consistently aimed in one direction.

    The setup that I would imagine working best would be a combination of the self-adjusting rig (that I haven't worked on a for a year or so), with a gimbal under the self adjusting part. In this way, your yaw is fixed according to the compass orientation of the line (with option to control with a servo), the fore/aft swinging of the pendulum is negated by the self-adjustment, leaving the gimbal to deal the small amount of remaining pitch adjustment that would occur with altitude change, and with roll adjustment which has plenty of torque against it's own weight on the lever of the pendulum to the line.

    self-adjusting-first-person-camera-rig-gs-1

  • @benedict - Careful about using momentum of something spinning for stabilizing. There's a problem there. If you combat a steady force with a force that depends on accelerating something, then the speed has to increase forever, which it can't. For example, if you give a gentle push on one side of the pan axis, the spinner would have to go faster and faster to resist it. Once it reaches it's top speed there's no more force exerted and it yields. If fans are involved it's different.

    @wargh
    I think we can push your idea further. If you assume a taught string, the yaw is fixed. But if you rotate your frame of reference to the kite line as one axis, then the other two axes are rotation around the string, and back-and-forth swing. The back and forth swing doesn't change much if the kite angle doesn't change. This could be passive, maybe a very over-damped joint. But then rather than driving the pan axis, maybe align the active axis with the kite line.
    I guess the difference is subtle. To put it another way, if you prevent the back and forth motion (toward and away from the kite), and the kite line prevents yaw, then the remaining motion is in pan and tilt and roll, depending how the camera is pointing (always two of those). But you can correct them all with one shaft aligned with the kite line.
    I guess it needs a drawing. Or a working prototype!

  • @hobbiestoomany -I have experimented with holding the pendulum in place fore/aft that in the past, but the results weren't great. The line is taught, but there is a lot of leverage through the pendulum. So as the kite line angle rises, you will put a kink in the kite line, and the angle of the pendulum will end up varying as tension changes. This can be counteracted by extending the distance between the anchor points, but the effect is still there. You can also pre-set an angle that you expect the kite line to be at, but this will also vary to a certain extent.

    That's why I ended up with the self adjusting rig. The load on the kite line is at one point, the pendulum is free to move fore/aft (, the feeler and pitch adjustment is all balanced, so this puts very little kink in the kite line (and associated oscillations).

    Matt
  • @wargh - I lost track of the cliff-running first person rig, but now I see it was you.
    http://arch.ced.berkeley.edu/kap/discuss/index.php?p=/discussion/3730/self-adjusting-first-person-camera-rig-gs-1-roll-stabilization/p1
    Do you have a picture of the rig? That is some very clean video. It made an impression on me last year, obviously.
    I agree that having it balanced is the key. To extend your ideas to all directions, and not just down the line, I think it might be helpful to think about the axes as they relate to the kite string, rather than the horizon.
    It probably doesn't matter for a 3 axis actively-compensated rig, but for two or 1, it may be helpful.

  • @hobbiestoomany -

    Here are some pics (the link was hidden in that thread somwhere) http://www.flickr.com/photos/32935499@N00/sets/72157628970140177/

    My use case was to get a stable video of sailboat from which I was flying the kite and rig. In that case I wanted the axis yaw always pointing towards the anchor point, which is easy given that the line does that for you. Likewise with pitch (minus a bit of sag), but that's what the self adjustment does. Roll is harder, but the GS-1 dealt with that pretty well. As such, the horizon wasn't ever a reference point for me. But if you're trying to stabilize a camera that is pointing in any arbitrary position, as you might want for normal kap photography, the horizon does matter, in which case you need to adjust somehow for the different angles of the kite line for pitch control. That's where accelerometers and gyros come into the picture, but the they only need to make minor adjustments vs the corrected macro adjustments of the pitch swing, and locked yaw.



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