PF L motor not working

[nerdsforprez]

Sorry I know this may have been asked before, but I could not find an appropriate thread.  

Driving my rock crawler build yesterday and one of the PF L motors just stopped working.  It is not a battery source problem, because the other three, plus the M motor for steering, all worked just fine.  

I had not been driving long, and there was a good amount of stress on the motor, but not to the point of stalling, at least not for any significant period of time or anything.  ANy ideas as to what could be the problem? 

[amorti]

Does it totally not react, or it shudders then is blocked? If blocked, some dirt got into the planetary gears and made them stop.

Make double sure it's not the power source, by plugging in other motors to that output.

After that: Cable or solder joint has a break, thermal fuse gave out, copper windings on the motor burnt.

In about that order of likeliness. I don't see the metal copper windings melting, the power here is too low and the fuse should catch long before that. But, it's still possible.

[Maaboo the Witch]

Just get a replacement off Bricklink.

[syclone]

IMho 99% it's the wire. Try wiggling it with a constant power source and if it starts working ther you have the problem. Also lego wire have awful coating - it crumbles within a few years. Maybe there's a short somewhere. 

If it's a wire and is close to the motor - cut it shorter and resolder. If it's somewhere or close to the plug I'd suggest getting a new plug off Ali or maybe a custom wire if your plug is the openable type (with latches, they changed it in the last years to be a solid piece). 

Mechanical issues are quite hard to come by - the planetary gears are closed off quite well, and the thermistor would've prevented any damage as it is quite weak. I mean, my m-motors were constantly used/tested in dirt/dust with small rocks outdoor environments and 100% of failures has been the wire.

[nerdsforprez]

23 minutes ago, amorti said:

Does it totally not react, or it shudders then is blocked? If blocked, some dirt got into the planetary gears and made them stop.

Make double sure it's not the power source, by plugging in other motors to that output.

After that: Cable or solder joint has a break, thermal fuse gave out, copper windings on the motor burnt.

In about that order of likeliness. I don't see the metal copper windings melting, the power here is too low and the fuse should catch long before that. But, it's still possible.

It shudders, then blocks I suppose.  But, totally driven indoors and only for a few moments before failure so I can't really imagine something getting into planetary gears.  Already checked power source, like I said, and it is not that.  

I don't see any wire issue.  If I can't fix things I may have to dissect the whole motor and see where the issue is.  

6 minutes ago, syclone said:

IMho 99% it's the wire. Try wiggling it with a constant power source and if it starts working ther you have the problem. Also lego wire have awful coating - it crumbles within a few years. Maybe there's a short somewhere. 

If it's a wire and is close to the motor - cut it shorter and resolder. If it's somewhere or close to the plug I'd suggest getting a new plug off Ali or maybe a custom wire if your plug is the openable type (with latches, they changed it in the last years to be a solid piece). 

Mechanical issues are quite hard to come by - the planetary gears are closed off quite well, and the thermistor would've prevented any damage as it is quite weak. I mean, my m-motors were constantly used/tested in dirt/dust with small rocks outdoor environments and 100% of failures has been the wire.

Good recommendation. I will try and get back.....

 

19 minutes ago, Maaboo35 said:

Just get a replacement off Bricklink.

HOnestly don't even know why you would bother making this comment.  Obviously I can replace if needed, I have like a billion of these motors.   The post had a purpose......to try and solve a problem....

[Maaboo the Witch]

10 minutes ago, nerdsforprez said:

HOnestly don't even know why you would bother making this comment.  Obviously I can replace if needed, I have like a billion of these motors.

Oh, do you? How nice for you! And how the bloody hell was I supposed to know that?

Don't be so rude.

12 minutes ago, nerdsforprez said:

The post had a purpose......to try and solve a problem....

You didn't make that clear at all.

[dr_spock]

Does the motor work connected directly to the PF battery box? 

You can test motor cable for continuity with a multimeter.  The motor is wired to the C1/C2 pins on the PF connector.

Non stalling stress can be enough to stop the motor from working, I had that with one of my GBCs.  There is a load protection inside the motor.

 

[amorti]

1 hour ago, nerdsforprez said:

It shudders, then blocks

So, given this, there's two possibilities. Neither of them involves a broken wire.

If you can't turn it easily by hand, then the planetary gears are damaged. If it's the gears, you can take it apart and look for dirt, damage, or misalignment.

If you can turn it easily by hand, then the thermal fuse has given up, and is triggering at very low heat. If it's the fuse, you can take it apart and either bridge it for zero protection, or replace the fuse with a new one.

Either way, it'll never be as strong after you open the clips, as usually you need to scrape them a bit flatter to get it open. So probably time to put it in the bin, however an autopsy would be interesting.

Edited August 9, 2021 by amorti

[nerdsforprez]

54 minutes ago, amorti said:

So, given this, there's two possibilities. Neither of them involves a broken wire.

If you can't turn it easily by hand, then the planetary gears are damaged. If it's the gears, you can take it apart and look for dirt, damage, or misalignment.

If you can turn it easily by hand, then the thermal fuse has given up, and is triggering at very low heat. If it's the fuse, you can take it apart and either bridge it for zero protection, or replace the fuse with a new one.

Either way, it'll never be as strong after you open the clips, as usually you need to scrape them a bit flatter to get it open. So probably time to put it in the bin, however an autopsy would be interesting.

Yup. Not the wires.  Inspected them well.   And I can easily turn by hand.  I will replace....but an autopsy should be fun....

[amorti]

3 minutes ago, nerdsforprez said:

Yup. Not the wires.  Inspected them well.   And I can easily turn by hand.  I will replace....but an autopsy should be fun....

Yep!

I'd be amazed if the motor windings have melted, but it could happen. That should be visible if yes, as it would have discoloured the copper.

Most likely, the thermal fuse has just had enough. The only quick and dirty test I can think of is to CAREFULLY bridge the two sides. Don't short them to the body of the motor! If it then works, you know where the fault was.
https://electronics.stackexchange.com/questions/531136/do-thermal-cutoff-fuses-wear-out-if-used-below-rated-temperature

Edited August 9, 2021 by amorti

[syclone]

1 hour ago, amorti said:

Either way, it'll never be as strong after you open the clips, as usually you need to scrape them a bit flatter to get it open. So probably time to put it in the bin, however an autopsy would be interesting.

We'll  that's very wasteful.  Even an XL motor being held only on one side has no issues running (and breaking gears in the drivetrain ) and looking up dissasembled l-motors, they're no that different. So no need to bin it if it's indeed the thermistor.

To open, don't scrape, push a small flathead screwdriver between the two parts of case where the clips are, pushing the outer shell (LBG) outwards and the clips (DBG) inwards. There'll ofcourse be a little damage to the clips and a slightly bent clip holder, but once reassembling use a pair of pliers to compress the motor from both sides where those holders are and it'll all be fine (not as new, but not a catastrophical failure)

Edited August 9, 2021 by syclone

[amorti]

44 minutes ago, syclone said:

 We'll  that's very wasteful.  Even an XL motor being held only on one side has no issues running (and breaking gears in the drivetrain ) and looking up dissasembled l-motors, they're no that different. So no need to bin it if it's indeed the thermistor.

To open, don't scrape, push a small flathead screwdriver between the two parts of case where the clips are, pushing the outer shell (LBG) outwards and the clips (DBG) inwards. There'll ofcourse be a little damage to the clips and a slightly bent clip holder, but once reassembling use a pair of pliers to compress the motor from both sides where those holders are and it'll all be fine (not as new, but not a catastrophical failure)

This is just by my experience of fixing servos, which I've done way too many times at this point.

You can't get them open without scraping away some of the latching plastic. Usually the latch on at least one side breaks. Once you're at that point, the motor will work again, but you can't use it structurally anymore.

For example in Madocca's PF Buggy the front end relies a lot on the strength of the servo, and if you crash it'll be fine, but after rebuilding the servo, it'll ping that apart. 
 

L motors may open easier - IDK, never tried.

Edited August 9, 2021 by amorti

[nerdsforprez]

Thxs both for your input.  I will try to salvage.... but if I can't no biggie....

Edited August 9, 2021 by nerdsforprez

[Toastie]

1 hour ago, nerdsforprez said:

Thxs both for your input.  I will try to salvage.... but if I can't no biggie....

Before you go there: @dr_spock's post is the way to go before using invasive methods. First a good diagnosis, then on to the blades, knifes, saws, Bunsen burners, etc.

Do you have a meter? Resistance between C1 and C2 is of interest - also when working that cable.

I am sure you have seen this: http://www.technicbricks.com/2012/08/tbs-technuggets-13-inside-pf-l-motor.html

With reference to this article, on the pictures of the opened motor, there is this one piece of additional electronics - it could be a thermistor, but I can't tell, as I can't zoom in nor is it clear where the wires are going. Should you take the surgery approach: Simply electrically shorten it, then let the motor run under some load (if it turns at all) by giving that axles a little work to do (two fingers ... or whatever).

As a rule of thumb: First dies the thermistor, and the motor is fine. 

Best
Thorsten 

Edited August 9, 2021 by Toastie

[dr_spock]

If you do take the motor apart, could you get the part number off the resistor?  I would like to know if it is the same as found in the PF M-motor. 

Tester shows 1.04 ohms for one from a bad PF M-motor.

 

 

[Toastie]

1 hour ago, dr_spock said:

could you get the part number off the resistor?

It is a PTC (thermistor), isn't it? Seems to be in series with the lead as it is for the M-motor (https://www.mikrocontroller.net/topic/267085). Yes, I know it is in German, but they conclude that the M-motor has a PTC in series. As all the other TLG motors have.

Your measurement shows R = 1 Ohm. At 500 mA, this thing needs to dissipate P = IR^2 = 0.5W, which will certainly heating it up "a bit" - which will increase the resistance, reduce the current. As R scales quadratically with P though, there is always a chance that such a device causes trouble, when running off from specs. As R(T) of the PTC goes through the roof at lets say 80°C or so (and then essentially shuts down the motor) there is this "in-between" region ...

This is interesting!

Best
Thorsten

[2GodBDGlory]

Right now, three of my four L-motors have been ripped apart and had wires resoldered. Personally, all of my PF motor breakdowns have been wires (except for Servo contact cleaning), but it sounds like your problem may be a little different (and already answered throroughly!)

EDIT: Apparently I don't know my collection as well as I thought! Only 1/4 L-motors has been repaired!

Edited August 15, 2021 by 2GodBDGlory

[Toastie]

1 minute ago, 2GodBDGlory said:

Personally, all of my PF motor breakdowns have been wires

This is most probably due to continued bending of the wires when running your models, right? Which is - as I am concerned - a design flaw, as motors are supposed to do something - in a "non-static" design like a car.

Also, I believe your experience does not relate to the wires themselves but the "joints", right?

Best,
Thorsten

[2GodBDGlory]

48 minutes ago, Toastie said:

This is most probably due to continued bending of the wires when running your models, right? Which is - as I am concerned - a design flaw, as motors are supposed to do something - in a "non-static" design like a car.

Also, I believe your experience does not relate to the wires themselves but the "joints", right?

Best,
Thorsten

Yes, the wear had been in the joints where the wire exits the plug or motor. It's annoying, but at least I'm good at fixing it by now!

[dr_spock]

Would adding strain relief help with the wires and/or using thicker gauge wires?

 

2 hours ago, Toastie said:

It is a PTC (thermistor), isn't it? Seems to be in series with the lead as it is for the M-motor (https://www.mikrocontroller.net/topic/267085). Yes, I know it is in German, but they conclude that the M-motor has a PTC in series. As all the other TLG motors have.

Your measurement shows R = 1 Ohm. At 500 mA, this thing needs to dissipate P = IR^2 = 0.5W, which will certainly heating it up "a bit" - which will increase the resistance, reduce the current. As R scales quadratically with P though, there is always a chance that such a device causes trouble, when running off from specs. As R(T) of the PTC goes through the roof at lets say 80°C or so (and then essentially shuts down the motor) there is this "in-between" region ...

This is interesting!

Best
Thorsten

That would explain why my wood chipper GBC module running off the 8110 Unimog M-motor PTO would stop working after a few minutes and work again after a few more minutes.  Dang drive line friction and heat. I was not having a ball running it at the Brickfete event. 

 

[Toastie]

21 hours ago, dr_spock said:

I was not having a ball running it at the Brickfete event.

Well then: Out with it! The PCTs are just there for the super-nervous TLG folks. Take it out, put a nifty temperature sensor hooked up to an Arduino clone onto the motor. When that temperature gets close to the melting point of ABS: Stop it. Or: Install a micro fan, blowing air over the motor when the going gets tough. I mean, a motor is a rock solid and very tolerant electromagnetic device, as compared to a nervous PTC. Or an H-bridge IC .

Tough tasks need solid solutions. Certainly not a nervous TLG motor, representative, lawyer, or sales person, or PTC.

Tough tasks need serious engineering, maybe pushing things a bit. 

Best
Thorsten