Electronics > Repair

Thinking on modifying my car door locks to brushless

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DavidAlfa:
My car is well known for its cursed door locks, the dreaded Mabuchi FC-280 motors die every 2-5 years.
Although it's a bit random, some doors will fail a lot faster than others after replacing the motor, although they all do the same work.
I blame it to Aliexpress quality but still better to change $4 twice than $150 in a new lock.

I already fixed them several times, but eventually any of the 4 doors will break again.
Then it's a f** mess, as the car tries to open the doors, one or more won't do so it'll close back.
You might fight it but after several tries the system will shutoff the remote for a while.

Of course I just ended using the feecking key, but it's a shame in winter with the wind, rain and all that, you want to get in/out fast! :-DD

So I've been doing some research trying to find a compact brushless solution fitting inside the lock itself, needing minimal modification.


Picturses of the door lock internals and the stupid motor:
 


It moves a reduction gear that later spins a worm gear, so it requires very little torque.

The central locking simply switches the polarity of the motor pins to close or open the lock.
My idea is to pass them through a rectifier, then use one of the unrectified wires to detect the direction and toggle the appropiate control pin.

A motor with built-in controller would be great, but I need it to be able to rotate in reverse.
I've found some, but still too big: The 2412/2418 are 24mm wide...
www.aliexpress.com/item/1005005389098818.html
www.aliexpress.com/item/1005002787368480.html

So far I haven't found smaller ones with integrated controller.

The second option is to get naked motors, using a external controller.
www.aliexpress.com/item/1005005368897031.html
www.aliexpress.com/item/1005005354667188.html

But the controllers I found either where too bulky, used some digital protocol or had no way to reverse the rotation.

I ended researching a simple BLDC driver and making a little pcb using the DRV10974, fitting in 13x7mm.
I know, I know, that cap-on-pin hack it's terrible, sacrifices to get it as small as possible ;)
The power will be about 2-3 amps at most, but only for2 seconds, I think the 1-Amp rectifier will survive that, not having time to heat up.

The adventure continues....

wasedadoc:
They are not exactly the same as your photo but I've had similar problems with the front passenger and two rear door locks in my Skoda. The only one that has never failed is the one that has the fallback option of inserting the key!

I've become quite adept at removing the locks, taking the motor out and cleaning the commutator and brushes,  The really nasty one is the front pasenger lock as removing the door trim and carrier panel looks to be impossible if the door is locked shut because the dashboard prevents access to some of the trim clips and carrier panel screws.

I took the precaution of intercepting the two motor wires in the loom behind the trim panel and adding extensions to bring them though the hole in the trim panel that is there for the electric window switch on the armrest/door-pull.  The interior of the armrest/door-pull is easily accessed and in there I have put connectors so that I can disconnect the motor from the car's electrics and instead apply external voltage. A quick dab of 20 to 30 Volts persuades an incalcitrant motor to spin and unlock

Shonky:
What is the failure mode?

Can you not just find a more reliable brushed motor of the same dimensions?

DavidAlfa:
The contactor contaminates/clogs up and no longer makes good contact.
Sometimes it arces and destroyes the motor, but so far I only saw that once, most simply had a thick layer of dirt.

I think the problem is caused by the short working cycles, the motor startup current is high, the brushes erode faster, but the motor never has a good spin to clean the dust/crap.
It's just 1/2 second, stop, 1/2second, stop...

lugaw:
That's adding more point of failure and complexity to the system.

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