Emergency Drone Motor Disconnect

[buta]

Most of COTS ESCs have only 2 wires from batteries so cutting ESC's MCU power requires to modify the ESCs.  OP's ESC is 60V 160A, it should have a voltage regulator to supply the MCU (60V to 3.3 V, 5 V or ..., linear or SMPS).  You can try to add a control signal to the voltage regulator circuit (if possible) to disconnect / disable the MCU supply.

If OP designs the fuse / crowbar, what is the rating of the fuse OP will select to ensure the fuse will not blow under any normal operations except halting forward flight?

I like the following EV protection devices.

You could consider a 'logic fuse'/'externally-triggered fuse'. We use them for Lithium pack secondary protection, a small heater energised via a third terminal blows the fuse in an emergency.

https://atcsemitec.co.uk/reliable-secondary-protection-for-battery-packs-in-high-current-applications/

That's really neat, I was wondering if that kind of thing existed.

....

[Berni]

Having difficulty finding anything on the cheap that will do the job in a single MOSFET or thyristor.

High current MOSFETs might claim 300A but then are lead-limited to 160A. Thyristors are looking at hundreds of dollars. Maybe I'm just not getting the parametric search right?

A few MOSFETs in parallel with a shared gate seems straight forward to me. Might introduce issues with load balancing between them? Not sure if there's other unforeseen issues with that.

For a short while it is fine to exceed that since it would take a while for the pin to melt. Go ahead and try to calculate what is the width of PCB traces required to carry such currents. You will get ridiculous numbers that don't even make sense. In reality you can just add lots of solder on them to give them thermal mass (Yes i know it does almost nothing for trace resistance, that is not the point here) and it will hold for the 10s or 100s of miliseconds it needs to survive it for.

Tyristors are not that expensive. Here is one that can do 700A peak for under 3 bucks:
https://www.digikey.si/en/products/detail/ween-semiconductors/BT155W-1200TQ/6680528

As for current sharing you can use the miliohm resistor that limits the current as separate resistors at each MOSFET to make each one of them see the same current. Each resistor can be smaller then

[james_s]

Most of COTS ESCs have only 2 wires from batteries so cutting ESC's MCU power requires to modify the ESCs.  OP's ESC is 60V 160A, it should have a voltage regulator to supply the MCU (60V to 3.3 V, 5 V or ..., linear or SMPS).  You can try to add a control signal to the voltage regulator circuit (if possible) to disconnect / disable the MCU supply.

Obviously it would require modifying the ESC, is that not an option?

[Jon_S]

That's really neat, I was wondering if that kind of thing existed.

The Littelfuse ones seem to take "<1 min" to operate, however.

The datasheet terminology is terrible, that 'cut time' at <1min is for a 2xIrated overload, not a cut via the heater.

The heater cut time depends on the heater power you can provide and the fuse size. They have graphs in each datasheet. It depends on the fuse size too, but they all seem to be under a second at reasonable heater powers. The little ones we use measured at about 100ms, from memory, with the heater being driven full chat.

Thinking about this application more, I would personally go for a pyrotechnic disconnect on the DC bus to the ESCs. It is the option that would cause the least hassle during an FMECA.   

[Siwastaja]

I'm not sure about cutting the ESC's microcontroller power - is that possible given the model linked in?

1) Find the 3.3V regulator on ESC board
2) Short the output with a MOSFET
3) ???
4) Profit

[buta]

Most of COTS ESCs have only 2 wires from batteries so cutting ESC's MCU power requires to modify the ESCs.  OP's ESC is 60V 160A, it should have a voltage regulator to supply the MCU (60V to 3.3 V, 5 V or ..., linear or SMPS).  You can try to add a control signal to the voltage regulator circuit (if possible) to disconnect / disable the MCU supply.

Obviously it would require modifying the ESC, is that not an option?

Technically it is a viable option for hobbyists.
But will it be a viable option for a commercial product, both both technical and commercial requirements should be considered, e.g.
will it void the ECS warranty
will it require re-testing for safety, EMC, ...
will it pass the reliability assessment
will it be cost effective
will the supplier develop a new model with OP's required safety feature if OP buys few K's per year
...

[james_s]

If it's a commercial product then have a batch of custom ESCs made. Many ESCs bring the 5V out on the input connector to power the radio receiver in a conventional model airplane, on that type you can short this to ground.

[buta]

If it's a commercial product then have a batch of custom ESCs made. Many ESCs bring the 5V out on the input connector to power the radio receiver in a conventional model airplane, on that type you can short this to ground.

It is Battery Elimination Circuit BEC which is common in RC planes' ESC.

I tested some high power ESCs from US, China and oz for heavy lift uavs, per my limited observations none of them has internal BEC.  I have not updated my ESC knowledge for a year, if you find high power ESCs with internal BEC, could you share with us.