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Old Feb 06, 2016, 11:36 AM
kb9nate is offline
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Caution using Gearbest/Chinese Gimball - Damages Receiver

Something I found out the hard way that I want to alert people too, is that the cheap gimbal a lot of people buy from gearbest/banggood and several other places can damage your receiver.

I bought the new L9R receiver and got it all set up in my model and just about ready to button it back up and go for a flight when I noticed that the RSSI on the OSD had dropped from 100% down to about 75%, I measured the voltage on the RSSI pin and it was only at about 2.5 volts.

Thinking that it was just a defective receiver I ordered another one, and while I was waiting for it to arrive took some voltage measurements on my other equipment, I found that the gimbal has 5 volts present on the signal wires for pitch and roll. None of the other electronics (FC/ESCs) have 5 volts on the signal pins.

It's a two part problem, a) the person that wrote the firmware for the cheap Chinese gimbal was an idiot and turned on the internal pull up resistors in the microcontroller which is what causes the 5v to be present on the signal pin. b) FrSky didn't design their receiver with any kind of protection on the signal pins, the microcontroller in the receiver can only handle up to 3.3v on the signal pins without being damaged.

Since I suspected the gimbal being the problem, when I got my replacement receiver I wired up everything but the gimbal, powered it up and checked the RSSI which was at 100% then momentarily connected one of the signal wires to the gimbal...same result, RSSI dropped to about 80% and now I have a 8ch receiver instead of 9ch. Luckily the rest of the chip seems to still be working this time, the last receiver got totally destroyed from it.

I did come up with a fix for the gimbal that works though, simply solder a pull down resistor from each signal pin of the gimbal to ground. A 10k resistor works good.

Buyer beware, it may not cause problems with every receiver, but it clearly destroys the L9R.
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