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Oct 19, 2021, 03:09 PM
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Mini-HowTo

FAST Ground FPV - Gimbal Frame


FAST OFFROAD FPV RC CARS!!

When it comes to FPV the better you can see the faster you can go! Which is maybe why we see so many fast street vehicles and crawlers out there. Camera shake tends to limit speed over rough terrain, larger vehicles have less of an issue with this, but will eventually experience it if driven towards the limits of performance. The solution I've found is to use a gimbal to smooth out most of the motion of the vehicle, also this can be configured to accept RC inputs for pan and tilt. The only limitation is that if the car rolls over the gimbal needs to be reset, however this can be done remotely, it’s not so bad. I'd love to write a step by step on how to duplicate my setup but that’s a bit much at the moment. Instead this is here to let you know that IT WORKS. The gimbal essentially mimics what your neck would do if you were sat in the vehicle, stabilize your head and eyes.

End up with something like this:


IT WORKS REALLY WELL! So do it, here are some general working principles to help ensure your success. Maybe I'm missing something but I can't see a better way to drive fast off-road FPV, even slow crawling over rocks is way more enjoyable as the view is not rolling around all over the place.

A search on aliexpress for 'storm32 3 axis gimbal' will pull up multiple sellers letting these units go for under $100CAD. The specific Storm32 board version I have experience with is 1.3x, it works and it’s the only one I've used so that’s what I have to recommend. Look at the pictures of the board and it will say the version number near the centre on the less busy side. The gimbals sold with motors and a frame are ideal to start with, however the frame will need to be replaced. Also it’s a good idea to replace the motor wires with something a little more stout as these failed pretty early on. Common servo extensions will do the trick, mine are fairy thick, a little too thick probably, keep a lot of extra line so it can bend easily.

Generally when designing the gimbal it needs to be balanced, rigid, light, and compact. Those are listed in order of importance. If the gimbal is not reasonably well balanced it will not be smooth, if the frame is bending it won’t be that smooth, if it’s heavy it'll destroy itself and not be smooth, etc. Ideally the camera would also be dead centre in the middle of all the rotating axis, however this is a lower priority. If possible keeping the camera mostly centered over the yaw axis is good. One last note, limit the travel of the gimbal mechanically. The last thing you want is the gimbal to turn 9023 degrees and tear all the wires out as it all goes cartwheeling downhill. I've done the cartwheeling bit, its FINE lol.

The gimbal runs best on 3s power however, a really lightweight camera setup can get away with 2s. Either way there is some effort needed to tune the PID parameters of the gimbal. I suck at it and managed to get it to work decently on 2s and 3s. Lots of resources online that can speak to this better than I can, like the Storm32 wiki.

Things to get:
  • Storm32 3 Axis gimbal, board version 1.3x, with motors and frame
  • Aluminum bar stock, a few feet of each of
    • 1"x1/8"
    • 3/4"x1/8"
    • 1/2"x1/16"
  • Mild steel bar stock, 1/2"x1/8" thick. This is for counter weights to balance the camera, other stuff could work too.
  • 2 servo extensions, about 12" is plenty. (Only the pitch and roll motors need new leads, the yaw motor wires stay static and haven’t given any trouble)
  • Aluminum sheet 4"x10"x1/16" this is to build the mounting deck. Design depends on the chassis it’s fitted to.
  • M2x6mm screws . I lucked into finding these at a local electronics shop. They have enough length to make it through the 1/8" aluminum and secure the gimbal motors.

Besides generic workshop tools I used a vice, drill press for putting holes in 1/8" sections, and propane torch (for the mild steel, do not use on aluminum or it will lose all its rigidity).

Start with something like this:
Last edited by JIPPERR; Oct 23, 2021 at 08:49 AM.
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Oct 29, 2021, 01:53 AM
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PID Tuning Process


So I recently removed the HD camera from the gimbal mount. I was making a lot of compromises to have it on there and the extension cable was playing havoc with the colours it was recording and I wasn't recording as much footage off it as I thought I would. So I rebalanced the gimbal and stuck it back on 2s power. Probably most fpv cameras could get away running on 2s, mine is already two cameras to start with as its a stereoscopic system (I love it, will have a separate blog on this at another time). I don't think too light would be a problem, the solution would be fairly easy if it was anyhow. So probably about 40g payload on the gimbal at the moment, and 2s power is just fine. I'm kind of harping on this a bit as the instructions indicate 3-4s power for the gimbal, but less voltage won't hurt anything here. The benefit is that the whole rest of the vehicle is running 2s so i can ditch another whole battery that was dedicated to running the gimbal and fpv gear. Less weight is more better!

PID TUNING Recipe here, PS none of the below will make sense unless you have some familiarity with the Storm32 GUI settings and the software open in front of you. Most of this from http://www.olliw.eu/storm32bgc-wiki/Tuning_Recipe with some exceptions as noted.

Setup the gimbal for tuning:
  • Turn off voltage compensation
  • battery voltage near storage level
  • Turn second imu to full **This differs from web page. I tried tuning with this set to off but big problems once i turned it on.**
  • configure to: hold hold hold
  • Disable all motors
  • set PID to 0,0,0 for all axis
  • Enable all motors
Adjust Vmax, try to move them by hand, the motors will resist motion. Try to find a minimum reasonable value, motors should not get warm. It proably doesn't need to be as strong as you think it should be. If the motors resist a little poke from one finger your probably fine. To high a voltage can make the gimbal difficult to tune. To low a voltage and you may experience the camera getting knocked out of position during rough driving, it will usually be able to correct itself. Check that the motors are strong enough to move wires!

PID Tuning
  • Tune in order pitch-->roll-->yaw
  • Tune in order D-->P-->I
  • Tune pitch (roll, yaw) axis
  • set PID values to 0,0,0
  • Increase D until it oscillates, reduce until stable and no buzz or noise, reduce one or two steps more.
  • Move gimbal around, reduce D further if noise or oscillation
  • Increase I to minimum non-zero value
  • Increase P to largest value without buzz or oscillation, then reduce it a little more
  • Increase I to largest value without buzz or oscillation, then reduce it a little more
Repeat for next axis, if buzz or shaking step back to previous setting and detune until its stable again

Once all three axis are done the BEEPS for the gimbal start up should sound really solid. Check how the gimbal functions in pan, pan, pan by putting the vehicle at extreme angles, it should be sortof able to deal with 90 degrees pitching up-down, and 60 degrees rolling left-right. If the gimbal start to glitch, vibrate or oscilate much before this you might want to revisit the PID settings. Disable the motors and enable individual ones to find where issues are coming from. At this stage it may be easier to use the simplified tuning settings or reduce Vmax to fine tune.

A bit more experimental but at this stage I also turned off the gyro LPF and set the IMU2FeedForwardLPF to 4ms, this made a noticeable difference to how it reacted at extreme angles. Experiment with yaw LPF as well.

Recheck with a fully charged battery!!

Tturn back on voltage correction, and set to pan pan pan, you are done!

This should result in a solid tune, able to stand up to very steep angles for at least short periods of time. 90degrees vertical should be do-able with some slow wobble in the gimbal.


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