So, it appears that if you flash your pre-2014 HobbyKing Multistar 30A ESCs with the SimonK kda.hex firmware they tend to overheat and catch fire…

Scroll to the bottom of the page if you want to skip the anecdote and go straight to the new hex file…

Only a matter of time…

Turnigy SK450 Deadcat QuadcopterI had flashed four Multistar 30A ESCs with the SimonK firmware when I first started building the SK450 Deadcat Quad. When I first started flying it I had a repeating problem that after a short period of flight the quad would suddenly drop out of the air.

At the time I put this down to ESCs overheating and used smaller props. Everything seemed fine although I never flew the quad for more than a few minutes at a time for fear of the problem returning.

Fast forward then to now and I had put the same ESCs (different motors) on my new spider FPV quad. On its first proper flight it dropped out of the sky after around 8 minutes airborne. I put that one down to battery as I wasn’t using a monitor at the time.

Back in the workshop I wanted to change the internals a bit and as part of this process I connected the power without having the ESCs connected to a receiver. They sat and beeped for a while until suddenly with a fizz a jet of flame sprang from the top of my quad!

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I didn’t really know what had happened but put it down to either a short circuit or my own stupidity. I replaced the burned out ESC with another flashed Multistar 30A and headed off down the field.

Once again, this time after only 5 mins flight and 2000mah out of the pack, the quad dropped like a stone when one motor suddenly quit…

I decided that I had over-propped the 1100kv motors and started pulling the frame apart once more as I intended to replace the motors. I decided on a whim to check the figures through my wattmeter and hooked up a motor to yet another flashed ESC. I was surprised to discover that, despite only pulling 6A through the ESC at 50% throttle, the heatsink was too hot to touch and I feared another fire…

So what’s going on?

I’m not an electronics whiz so I don’t completely understand the deal with these ESCs. I went and did some research on the internet and it is all to do with the FETs and p-FETs and n-FETs and currents not turning off in time during the increased cycle rate of the SimonK firmware.

This is only affecting the BEC version of the Multistar 30A ESC, the OPTO version is fine. Also, it is only affecting the first version of the type that look like the pictures below (mine say “100” on that grey square bit BTW).

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It appears that the reason I never had a fire on the SK450 is because the ESCs were out on the arms and under the prop-wash. Once I moved them to the FPV quad they were inside the frame and with less cooling it was only a matter of time before kaboom!

Can it be fixed?

I’m still testing but it appears it can! I found a thread on Github discussing the problem (view it here). A lovely programmer calling himself “KHudson” has posted a new hex file that when flashed to the ESC does indeed seem to fix the issue and after a few minutes at a steady 50% throttle the test ESC was only a little warm.

Download the new multistar.hex file here

If you have already flashed your ESCs to get this problem then you know how to flash this new firmware.

Good luck and let me know how you go…

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