Lehner 3080 / 8 Brushless Motor ? fault

[mohanjude]

I have been running this motor on a FG monster truck coupled to a schulze 40.160 controller on 10s 6000ma Lipos. However on low rpm the motor stops turning on Load - it stalls. Once the motor stops turning increasing throttle does not help it get moving. It is as if the rotor is locked or stalled. The only way to get the motor moving again is to bring the controller back to neutral and throttle it. If I throttle it hard or load the motor after it has picked up speed it will keep moving past. The motor will accelerate freely to its top rpm but does not like been loaded on low rpm. Once the motor has picked up speed the load does not appear to affect it.

Basically the motor cannot spin from dead on a load but will turn the load once it has picked up speed. In practice it means holding the truck off the ground letting the wheels spin and then dropping the truck. The other way is to push the truck and then accelerate away. Once the truck is moving it will pick up speed quickly and get upto 40mph rapidly.

I coupled this motor with a BK controller 36150 and was running it fine but after 5minutes the controller caught fire when I tried to move from standstill.


Any thoughts? I know the schulze is not faulty as it runs a Plettenber Bolido no problems.

Mohan

[_paralyzed_]

I know to run the bolido with the schulze you need high timing. If the lehner is a 2 pole it should have lower timing, but I don't think that would cause what you describe. A smaller pinion is a good place to start

[mohanjude]

I took the motor out of the car and placed it on the bench. I then connected it to a pulse generator (servo tester). At the neutral it is 0.150 - when I turn it up to say 0.154 the motor starts spinning slowly - you can actually stop the shaft turning by holding between your fingers (at this stage the motor probably has about 100 rpm). when you take the hand off the shaft stays stopped. If I turn the pulse upto say 0.160 the motor spins up faster and the shaft cannot be stopped by hand or stalled.

A large brushless motor should have a lot of torque even at low rpm ?

[_paralyzed_]

smaller pinion or more voltage

[suicideneil]

I dont think lack of torque is the issue here, you seem to be describing the issue that affects high pole count motors in that they have trouble getting moving from a standstill (thinking outrunners mainly but this isnt that far off for all intents and purposes). Higher start power would help, and high timing if those are options on the schulze. If you stall the motor when it isnt turning terribly fast, the esc will 'loose' the rotor posistion and have trouble getting it spinning again, but as you noted once its spinning past a certain velocity you wont be able to stall it terribly easily.

Have a play with a few settings, maybe lower the gearing a tad, but if all else fails there isnt anything wrong with giving the truck a boot to get it moving- is there is adjustable deadband on the radio, maybe try lowering that too.

[_paralyzed_]

would changing the winding configuration help? i.e. delta vs. wye?

[mohanjude]

All the above suggestions are very helpful. This is a Lehner so I think it is 2 Poles?

I intially tried the Delta configuration by attaching 2 leads each to adjacent connectors (yields 984 odd KV). Then I changed it to Y by attaching only 3 leads from the speedo and connecting the remaining 3 connectors as a star (yields 580 odd KV)

Remember the motor is now on the bench. I am holding the shaft with my hand. I think what Neil said is true - it loses position. What puzzles me is that this motor weighs a ton, is as big as a beer can and yet at low rpm I can stall it with my bare fingers. The dead band thing could be a issue. What concerned me is that I switched to my Schulze 40.160 from a BK elektronics 36.150 (rated 150 amps and rated 42V). I switched because the truck was running fine on this controller until it decided to catch fire while I was trying to move from standstill. I wasn't pushing the controller or doing high speed runs. In fact I had less than 2 mins on this controller. This was a very expensive 2 minutes as the controller cost me several hundred Euros. I am wondering if the controller caught fire because the rotor was 'locked' in position and was drawing AMPS +++ .

The Schulze controller is an automatic configuring controller - ie you dont even have the chance of setting the maximum and low position of throttle like standard controller. It simply locks onto neutral. In the BK controller at least you can chose max throttle and full brake positions by taking off the jumper. On the schulze the only options you can change are on a jumper and the only worthwhile options that remain to be changed are timing high /low and gearing high/low. I dont want to touch the 'frequency' DIP switch.

The motor runs freely on the bench. Here is my stupid hypothesis. If say one of the windings in the phases is faulty will it cause the motor to stall at that position or perhaps not feedback to the controller?

I am thinking if say for example once the motor has momentum can say 2 of 3 the phases compensate due to the inertia of the rotor? A bit like a misfiring cylinder in a car engine will cause the engine to turn over but lack power / torque?

I have never managed to stop a shaft of a brushless motor with my fingers and I am really miffed that I can do this with the biggest 10KW brushless motor that I have owned.

I can pair the motor back with another BK controller that I have but I dont really want to toast it in case there is a problem with the motor. Is there a simple way of checking say resistance etc

Mohan

[What's_nitro?]

It's the controller that's the problem. Motors are (for the most part) passive devices. Something like this where the motor stops at low speed and wont start sounds like, as others have suggested, a commutation problem, or, start power is too low. I would bank on the latter since you can stop it by hand at low speed. It could be a radio issue, IDK maybe the endpoints the controller was programmed to became corrupted so it's missing a few steps on the low end (in the ESC, not your Tx). I'm assuming the motor has no binding at all at any point, and there are no shorts in it's windings.

[mohanjude]

thanks for the reply - I will give the motor a try with the other BK controller (36.150). I know the schulze is not faulty as it runs other multi pole motors without any issues. I think the Lehner motor and this Schulze controller have some compatibilty issues. I can only assume that the previous BK controller caught fire and destroyed itself due to bad luck rather than a motor problem.

That ESC was rated for 150 amps and 42 volts. Running it on Enerland 25C 10S packs 6000ma should not have been a limiting factor as clearly the lipos can supply 150amps. However something went wrong and controller caught fire in 2 mins after trying to pull away. I am just worried that my remaining BK controller will catch fire if I cannot isolate the reason for the controllers spontaneous combustion. Luckily I managed to save the lipos, receivers - the aluminium roll cage / frame didn't do that well.

[_paralyzed_]

IMO motors either work or they don't, of course there are exceptions, but for the most part I believe this to be true. I know this is a super big super expensive setup, if this was happening to me I would start with the basics as I stated before, a smaller pinion or more voltage. If neither helps at all I would think it's a motor problem.

[What's_nitro?]

It could be the Shulze is about to go Mt. St. Helens on you and this is a warning... Lets hope not.

[_paralyzed_]

Originally Posted by What's_nitro?

It could be the Shulze is about to go Mt. St. Helens on you and this is a warning... Lets hope not.

I haven't heard of any 40.160's having problems. It was the 18.97's that torched, and he mentioned it works fine with the bolido........

[mohanjude]

Originally Posted by _paralyzed_

I haven't heard of any 40.160's having problems. It was the 18.97's that torched, and he mentioned it works fine with the bolido........

You are right - 40.160 works fine with the Bolido. Just dragging my hels on whether to connect the remaining BK controller to this motor to see if it makes a pretty firework. I was going to take my video camera but didnt get a chance to film the debut run - it would have made one heck of a video or maybe not...

[lincpimp]

Motor may have demagged... There is a method of testing the phases against the can to check for shorts, and there must be some sort of resistance spec. If two of the phases are shorted it would act as a brake on the motor, and would also cause some massive current draw thru the esc. I would investigate the motor further. Did you buy it new, or used? Any physical damage?

[transtalon]

I had a similar problem with my old setup for my 5" extended Lst2. I wanted to make the Lst2 to go fast on the topend I geared it to high and the same
thing happen but with a lot cheaper components, KB45, Hydra 240 and watercooling setup. I put a +6 pinion on it with a 6S 8k lipo. I think you need to gear it down on your setup. How much does the FG weigh with everything on it? I learned that quick reaction saves other components from going.