04.02.2016, 18:43 by Gal

I have finished my gimbal project for Garmin Virb Elite action camera and I’ll try to explain how it works and what parts I used.

This is how it looks.

Motors are BLDC with very low KV. All three are alike and have hollow shaft. This enabled me to get wires through the motor shaft and make an improvised slip ring. This solution is capable of few turns in either direction before wires twist too much. All frame parts were machined from aluminum on 3-axis CNC mill. Fortunately I got the design right the first try and I did not have to machine any parts again. I made slots in the design to get little adjustments for gimbal’s center of gravity possible. I was able to get it almost perfect which was more than enough for motors to compensate. Machining took me about a day in the workshop.

I reverse engineered original mount that came with the camera and designed my own camera plate as I call it to always keep tha camera in the same position on gimbal. Those three teeth at edge of the part were my solution. I also cut out some material to preserve unnecessary weight of the part. Camera is tied to the plate with a small velcro.

I bought genuine USB cable from Garmin and tore it apart to figure out the pinout. If you like to know more about it, I wrote more here. Camera is outputting live analog video feed through USB. I can also connect external microphone. Port left to the USB on the picture is HDMI. Unfortunately it works in playback mode (no live streaming).

After some time of using my gimbal I added pitch control. IT consist of two 8x8mm SMD buttons in the CNC machined aluminum housing. I also engraved two arrows to make it easier to use for someone who isn’t familiar with such device. To keep the number of wires through motor shaft as low as possible I made a simple resistor divider in parallel with buttons to get all three states of control through only one wire (3.3V=camera tilts up, 3.3V/2=nothing, 0V=camera tilts down).

I decided to go with DB9 connector for charging the 3S LiPo battery inside. I only required 4 pins for charging and DB9 has 9. I used the rest 5 pins for 2 RC channels (so I can connect a RC receiver and control the gimbal with it as shown in this video), analog video output (so I can connect external monitor or wireless video transmitter), microphone input and a control button for changing programmable modes of the gimbal operation.

I also made a video transmitter module with a RC receiver. I smiply plug this module in the charging port of my gimbal. It consists of 5.8GHz video transmitter made with boscam module and Frsky 4 channel receiver. You can see its antenna next to the SMA connector of cloverleaf anetnna for video.

I used 3 axis SimpleBGC gimbal controller. It met all expectations and connections was very straightforward. I removed all connectors and soldered wires directly to the PCB to eliminate connector failure possibility and to save some space. Controller uses two sensors (one under the camera and one on the frame) to better determine in what position motors are and greatly increase working angles. Although the controller was expensive I have no regrets buying it because it simply works. Note that I had bad experiance with fakes from ebay before buying genuine one.

SmpleBCG gimbal controller

Here are my current PID settings. It took me some time to get them right. Auto PID helps to get it near perfection but it still needs some human correction. I have follow mode enabled on yaw axis with a deadband of 15°.

First run of the gimbal after getting settings nearly right.

Test outside with gimbal mounted on 3m long pole.

Video demonstrating pitch control.

Pinout of the USB cable on Garmin Virb Elite.

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Download CAD files from Grabcad here

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Part list:

Motors: Rctimer GBM2804 Hollow Shaft

Controller: 32 bit basecam

Battery: I made a 3S pack from 3 4500mAh LiPo cells

DB9 connector, 2 pole switch

10, 6 and 4 mm aluminum sheet for frame

11mm POM plastic for electronics housing

4mm oak wood

few bolts and screws

Video transmitter module