Thinking on modifying my car door locks to brushless

[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!

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.

[CatalinaWOW]

These door locks are a problem on most older vehicles.  The ones I own and work on have a different configuration, but the same basic idea.  The failure mode on them hasn't been in the motor, but in the gear train, with dirt and dried lubricant increasing the friction beyond the motors capability.  Clean and lube of the gear train solves the problem for a few more years.

As an aside, one of these had a clever variation on the commutator design.  Instead of the usual strips of copper parallel to the shaft the commutator was moved to a disk shaped pc board on the end of the windings.  Gave a lot more surface area, so maybe less susceptible to contamination.

[DavidAlfa]

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

Why? It's the only failure in this locks. Every one I fixed looked brand new inside, full of fresh grease, no wear, perfect gears, nothing else than the motor.
By removing the mechanical contacts, should finally last forever.

[james_s]

My 33 and and 38 year old Volvos have very similar door lock motors, I've had a wire come loose in one once but I've never had one of the motors fail, ever. Have you taken one apart to determine why yours are failing? The duty cycle is extremely low, even if the motor is only rated to last a few hours it should outlast the car in almost all cases.

[DavidAlfa]

I already said, the rotor contacts end with a layer of dirt.
No damage, it's like hard, dark paint.
There's no grease entering the motor, so it must be the carbon brushes, adding the fact the motor only rotates maybe 50 turns every time.

[james_s]

Maybe try to find a Volvo 200/700/900 lock motor assembly and adapt it to fit? As I said I've never had one fail and there have been quite a few of those cars in my family including a 240 my mother bought brand new in 1986 and still has.

[amyk]

Check the electrical system voltage. It might be shortening the life of the motors by being too high.

If you're really inclined to mod it, I'd try to use a solenoid instead of a motor.

[Whales]

I think that either changing to brushless or replacing with a different model of brushed motor would both be good things to try.  Go for whatever is easier to get your hands on.

Trying to understand these small brushed motors

Getting datasheets for Mabuchi motors is hard.  Sometimes you can find random ones on the web, but they're often for a slightly different model number compared with what you can buy or have (and I don't think consecutive numbers/letters mean models are similar).  Perhaps they change so many params for each customer that each customer gets a unique model number?

Try page 53 onwards of this doc (it's the biggest I've found):

http://home.mlab.cz/Downloads/PDF/datasheets/Mabuchi_Motors_Complete.pdf

Note the atrocious efficiency: many of these don't even hit n=0.5 at any point of their perf curves!

I suspect that window door locks will use the absolute cheapest models possible, they have lots of gearing so they don't need to do much.  There is a massive difference in performance (speed, torque, impedence, bearings) available in this one form factor.  I've had some motors from an old fixed-wing toy craft that were amazin, some cheap Mabuchi's from Aliexpress that were pathetic and some mediocre greymarket ones from another site.

[DavidAlfa]

I'm also open to try a different motor, however it's almost impossible to know which one to get, all are sold as "high quality, long life, made with gold" and all that.
With brushless, I know 100% it's going to last unless the electronics blow apart.

[Psi]

There's a few options.

Those motors are a standard size, so getting a good quality version is probably the first thing to try.

Another thing is to add like 6 diodes in series with the motor to drop the voltage 4.5V or so.
I wouldn't put it past aliexpress to overstate the motor's voltage. And given this is a car the battery is at like 14V with the engine running, so you're already putting 2V more into the motors if the engine is going when they lock/unlock.
And that assuming they could handle 12V to start with.

Another option I would be tempted with is those Tamiya mini motors intended for those tiny race cars.   See attached pic.  Sadly they are 3V not 12V so you'd need some electronics to step the voltage down while keeping the fwd/rev control.  Main reason i think they might be a good option is they are build with higher quality than your standard aliexpress motor and intended to be run hard albeit for a short time.

[DavidAlfa]

What is that standard size called?
The 130 has same shape but it's 20mm.
So far I only found those 24x18mm from Mabuchi.

[Whales]

I also call them "130" motors, but there are also lots of other model numbers with the exact same size (or the same cross-section but a different length).  I'd love to know if there is a better name.

I wouldn't put it past aliexpress to overstate the motor's voltage. And given this is a car the battery is at like 14V with the engine running, so you're already putting 2V more into the motors if the engine is going when they lock/unlock.

Good point.  I know that some small brushed DC motors sound less happy and arc more at higher voltages (but I'm not sure if this is a universal rule).  Perhaps undervolting them slightly might be good.  They would be designed to work even with a somewhat flat battery, so there is probably a good tolerance range for operation.

[Psi]

Those motors are sold in a few different voltage ranges
Like 3V 6V 9V 12V etc.  and I would not put it past cheap manufacturers of them to decide to stop making the 12V version and sell the 9V one as 12V instead.
Or maybe design a new 10.5V one that they believe and handle both 9V and 12V applications just to cut down on the number of sku's they need. etc...

[sokoloff]

I've changed about 6 of these actuators on my wife's 2005 CR-V (5 doors) in the last 11 years. I thought it was just a Honda fault, so I'm slightly relieved to hear other manufacturers having issues as well.

Even with the prospect of changing each lock actuator every 5 or so years, I'd never spend the time trying to improve the part. The NRE time just won't ever come close to paying back.

[DavidAlfa]

Well, lots of people are having this issue, havign to pay $150 every time.
This car production ended in 2006, but there's still some people around with it.
I guess it could be a small niche business, selling improved locks that won't fail  .

[sokoloff]

Ah. Mine are $15 and 15 minutes to change.

[wasedadoc]

Ah. Mine are $15 and 15 minutes to change.

The item at that link does not include the motor and other bits.

[coppice]

I've changed about 6 of these actuators on my wife's 2005 CR-V (5 doors) in the last 11 years. I thought it was just a Honda fault, so I'm slightly relieved to hear other manufacturers having issues as well.

Relieved is a strange term to use. You are content that if you get a different car next time, things will be just as bad?

[coppice]

My 33 and and 38 year old Volvos have very similar door lock motors, I've had a wire come loose in one once but I've never had one of the motors fail, ever. Have you taken one apart to determine why yours are failing? The duty cycle is extremely low, even if the motor is only rated to last a few hours it should outlast the car in almost all cases.

Interesting. I'm pretty sure the Volvo 740 I bought 38 years ago, when they first launched, used solenoids for the door locks. It made a very solid clunk when the locks fired, and I had to service one of them. The little PCB that timed the pulse had an issue. I can't remember what IC they had on that board, but I remember it was a 0C-70C rated commercial part. That seemed very unsatisfactory for a car made in Gothenburg.

[sokoloff]

Ah. Mine are $15 and 15 minutes to change.

The item at that link does not include the motor and other bits.

I assure you that it does. I installed one of that exact listing a few months ago.

[DavidAlfa]

This motor looks pretty good to me... Any thoughts?

https://www.aliexpress.com/item/1005002326133663.html