short circuiting motor phases via automotive relay and RF remote for safety

MY got stolen

While I wait for it to be returned I've got to build the second child of mine.
I need as many security features and blo0ddy possible. How can I safely short circuit phase wires in unpowered state, so bloody Fxxxx can not wheel,cycle it and I 'll have ground anchor and bloody heavy cut resistant chain next time.

Wouldn't you just get a controller with regen braking and use your relay to emulate a pulled brake lever? That's about the most an electrical system can do to resist movement. A $20 beeping disc brake lock would do more though, anyway:

So not really worth the cost of the relay. Unless you are trying to permanently destroy the bike at the press of a button. For that you'd need a cellular data module or dead man's switch on a timer before having it short the battery between the battery connection to the BMS, so no protections activate, I guess.

There are threads about doing exactly this (perhaps minus the RF remote); i don't know if anyone ever implemented it, but the technical details are there, if you look around.


There's also discussion of the potential problems, such as that relays can chatter from vibration, and if this happens during a ride sufficiently to allow a short while in motion, it will blow up your controller and add significant plug-braking drag to the wheel, which could cause you loss of control. Or if the remote system somehow activated while riding; it would be even worse with all three phases shorted.

It will also blow up the controller if the shorting system is still activated and the thief manages to turn the system on and try to run the motor. They won't be able to ride away, but neither will you. (and if the controller failure is a complete shoot-thru it will short the battery itself out, which if your protections against that are inadequate could cause a battery fire and destroy the whole thing, as well as whatever is near it).



You can design it so that the controller is disconnected when the relay activates, but this means the relay has to carry the entire full-load worst-case phase currents, too, and that's a fairly big relay compared to what you need to just short the phases enough to make the wheel very hard to turn from a stop.


Instead, if you really want to lock the motor by phase shorting, I'd recommend using a motor-to-controller phase connection that requires a removable bridge connector, and the two halves of the on-bike are connectors that cannot plug into each other, and can't be connected via simple wire bridges stuck into the pins, should a thief know enough to be able to do that. That way you can remove that connector when you walk away from the bike, which leaves it unable to be driven by the controller. Then you can have a shorting plug to connect to just the motor side in it's place, that is wired to connect all three phases together.



They can still pick the bike up and walk away with it, or toss it in the back of a truck, van, SUV, etc., they do that with full-size motorcycles.

If they really want to steal it, they will, no matter what you do, other than having a human you trust guarding it, or never leaving it.


If you make it less desirable-looking, it may make them go to the next one over, but if it's the best target wherever it is, they'll go after it. There are a number of threads about anti-theft measures as well, of all types, from locks to uglification to stealth.

lnanek said:

Wouldn't you just get a controller with regen braking and use your relay to emulate a pulled brake lever? That's about the most an electrical system can do to resist movement.

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Depends on the type of braking the controller does.

If it's one that has FOC and actively fights the wheel rotation, using power from the battery to do this, rather than regen braking, it would be the most possible antirotation force.

If it's typical regen, then it will do very little to brake the wheel from a stop, and only make it really hard to ride as it spins faster and faster.

Many regen-type controllers also dont' brake down to zero (or above a certain speed), so they wouldn't even do anything when the bike is stopped.

The disadvantage of this is that all the thief has to do is disconnect the brake wire that's being shorted, and the bike is already on and ready to ride.

Same for the many controllers that include an antitheft wheel-lock function that does the same type of job--once the antitheft wire is disconnected, off they go with your bike.

How about locking the wheels? You could install a couple of hydraulic brake line locks and lock both wheels. Might be hard to hide on the front, but it looks like there are places along the rear line to conceal one.

I thought about shorting the phases, but it seemed problematic, and I couldn't think of anything foolproof. In the end, there’s not much you can do if the bike is light enough to lift into the back of a truck.

You could use a large double pole relay to short the phase wires, but there should also be some kind of lockout to prevent the controller from turning on when the relay is closed. The relay will also need to be powered with a dc-dc or find one with a coil voltage that matches your pack. Another option would be a hidden switch that shorts the phases.

fechter said:

Another option would be a hidden switch that shorts the phases.

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I thought about that option, with a double pole switch, so it interrupts the controller on/off as well. You could probably get fancy and add a remote.
How much force does the locked up the wheel need to withstand, before the thief gives up? Maybe just a little more than is required to skid the tire when they are pushing it? I never tested it, but I was thinking the conductors used to short the phases can be relatively light duty (when my controller blew and shorted the phases, I couldn't push my bike, and quickly disconnected the phase wires, and started pedaling. I reached down and tried to turn the wheel, but I'm guessing a little 22ga wire might have been enough to withstand that).

Will shorting the phase wires do anything with the controller disconnected? It sounds like, when they are all shorted together and have power flowing into them, all the magnets are on and lock the wheel in place, instead the magnets being on sequentially in turn to make it move. If you disconnect the controller, there won't be any battery power on the phase lines to turn all the electromagnets on at the same time any more. So it's more like you have to both disconnect the controller and connect the battery directly. Sounds like a big battery drain unless you also trigger it from an accelerometer detecting movement.

Just try it.

The amount of turning resistance depends on the motor, gearing, etc. I tried it with my Sur-ron just using some jumper wires and while you can still move the motor, it would be very hard to get far with it. I've seen controllers that actively resist the motor turning and effectively lock the wheel, but they need to be constantly powered on to do this.

fechter said:

Just try it.

The amount of turning resistance depends on the motor, gearing, etc. I tried it with my Sur-ron just using some jumper wires and while you can still move the motor, it would be very hard to get far with it. I've seen controllers that actively resist the motor turning and effectively lock the wheel, but they need to be constantly powered on to do this.

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On my Leaf hub, I could turn it very slowly by hand, but the tire would skid if I pushed the bike. Of course if the thief were one of us, then we’d just disconnect the motor harness or cut it.
I have to do tire maintenance this week so I’ll try shorting the phases with some 20 gauge wire and see if there’s any issues locking the wheel with a small conductor like that. Maybe it could even be fused.

If you push it hard, I wouldn't be surprised if you can burn a 20ga wire.

lnanek said:

Will shorting the phase wires do anything with the controller disconnected?

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Yes. It's why it is very hard to turn a wheel when a controller blows up it's FETs, shorting the phases together; same when the motor cable gets damaged at the axle exit doing this.

You wouldn't want to short them with the controller connected, as if you power up the controller it will then blow it up.

lnanek said:

It sounds like, when they are all shorted together and have power flowing into them, all the magnets are on and lock the wheel in place, instead the magnets being on sequentially in turn to make it move.

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If the phases (or any wires) are shorted together you can't have power flowing into them, there's no circuit for that to happen wih the short present; it reroutes all the current before it ever gets to them.

Power would instead flow directly from the out of whatever supplies the power and back into the in, blowing up whatever supplied the power (the controller, in thsi case).

lnanek said:

If you disconnect the controller, there won't be any battery power on the phase lines to turn all the electromagnets on at the same time any more. So it's more like you have to both disconnect the controller and connect the battery directly. Sounds like a big battery drain unless you also trigger it from an accelerometer detecting movement.

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The systems that have antitheft functions to actively fight wheel rotation simply don't do anythign until you try to turn the wheel, then they detect this with the hall sensors, or the normal sensorless routines via phase wires, and then begin applying current as needed to fight the rotation.

None of them turn all the phases on at the same time.

My security is a 'Sold Secure Diamond' U-lock and a cable to reach the front wheels to slow them down, but I'd like opinions on an idea.

I've identified a switch into the controller on my trike which sets the motor to reverse. I am working out a switch and location - my idea is I can reach the switch with one hand, and the throttle with the other, and also that the switch is not obvious (such as under the seat), and also not momentary.

I have the thought that leaving reverse engaged buys me some time as anyone attempting to ride it away (without awareness of the switch) would be in reverse at about 6km/hour. Fine, it's a funny thought.

But are there any real concerns about this set up?

offGridDownUnder said:

But are there any real concerns about this set up?

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As long as the switch cannot engage during a ride, accidentally switching into reverse while ridng forward. (a line from one of the HHGTTG books comes to mind) :/

Or the controller is designed so that you must come to a complete stop before it will change modes (some are, some aren't).

I use AirTags. They’re great little gadgets. It’s just a pity that so many people are paranoid and disable the Find My feature.