Odd brushless problem!

[DaveG28]

Had a weird problem with my electrics last weekend, and want to guage opinion on what might be the problem:

In two races last sunday within a couple of laps of the start, coming off one of the jumps my motor died. After a few seconds it started back up going very slowly, and worryingly from this point the throttle was stuck on at a low speed no matter what I did with the stick (including trying to brake ).

Both times when it was switched off and back on it then went fine again, through to the end of the race too without the problem coming back.

I am guessing it can't be thermalling because its happening near the start of runs, and because I wouldn't expect it to fix itself and then run a firther 3 or 4 min without problems.

Someone suggested sensor wire (didn't have spares with me) so am planning to swap sensor wires before running this next weekend, but it seems odd to me again that the problem didn't then replicate more often?

Anyone got any ideas on likely causes???

Kit I'm running is:

LRP TC Sphere 2007
LRP 4.5 can with 13mm sintered rotor inside
Spektrum micro receiver
running in 4wd class (an Aero)

Cheers all,

Dave

[sparrow.2]

Off the top of my head I'd have thought it might be a motor sensor problem. Either the sensor wire on the motor or the sensor in the motor itself. Other explanatiosn might be the capacitor being bust on the speedo or even dirt in the speedo or receiver...

Good luck

[SlowOne]

What was the steering servo doing at that time? Did it work normally?

[DaveG28]

Steering worked fine!

Is it possible I've damaged the sensor from the inside when changing rotors?

[DCM]

it sounds like the esc is losing site of the rotor position, so it waits till it finds this, this is a problem normally found in a sensoreless system, so the first thing I would check is the sensor lead. If that is all ok, you may want to pull the motor apart and check it and give it a good clean through....

[MattW]

When LRP speedo loses the sensor position, it just cuts the motor, and lights flash in the appropiate sequence. It will also usually emit a high pitch "squeel".

I'd be suspicions of the Spectrum reciever..........because i always am when i hear of a spectrum system playing up!!

[DCM]

if the steering had stopped to, I would of said Spektrum too, but it sounds like the LRP is just lost....

[RURC]

I have been seeing this a lot at the tracks in the states. Switch it off and on and it goes away for a while. I have been seeing it on the lrp and speed passion systems only. I have not seen a Novak or Tekin doing it. DCM says that it is loosing rotor position but I dont see that holding water. Because if it looses position it should pick it back up on the next pulse from the motor. With sensorless this is not a problem. I have sensorless controllers from almost every maker and when they loose position they only do it for a moment, just like the sensored one should do. Since I am seeing it from different manufacturers I really just think that, like your computer it is just loosing its mind and needs to be reset. I dont mean that you should accept this kind of performance but it could be caused by many things including a voltage problem. What batteries are you using? Really check your connections, all of them. Get the Spekturm telemetry unit and monitor your battery. I use an Eagle Tree system but the Spektrum should work well also and is a lot cheaper.

[RURC]

Sorry forgot to subscribe

[DCM]

the pulse doesn't get generated without a known rotor position, when that happens, you can get rollback or just pause, it is because of the sudden loss of motion, the esc can't work out which coil to energise.

[racingdwarf]

Just a thought, but are you running a spectrum capacitor?(spelling). I had loads of probs with a micro Rx untill I ran one........now sorted.

[RURC]

Originally Posted by DCM

the pulse doesn't get generated without a known rotor position, when that happens, you can get rollback or just pause, it is because of the sudden loss of motion, the esc can't work out which coil to energise.

You are correct in that the energizing of the correct leg dose not happen without knowing the rotor position. The premise of your statement is very close but this is not completely correct with sensored brushless systems. And even in sensorless it is not 100% true. I will explain...

Sensorless systems send a signal that "tests" the rotor location. This takes pico seconds. Then they fire the appropriate leg (L1, L2, or L3) to generate the desired rotational direction. This result is "tested" again to insure that the correct direction has hit. This is correct than 90% of the time. Except for Tekin (sensorless ESC's) and Castle Creations, they enjoy a correct rate of more than 98% because of the algorithms they employ.

In a sensored system this dose not happen (this gentleman and the ones I have seen this problem in are sensored) In sensored systems there is a hall effect (magnetic) sensor array that gives precise position to the ESC at ALL TIMES, even at rest. There is no "test". The ESC is receiving rotor position information and using that information to control the motor rotation and speed.

As far as loss of motion causing a loss that is really irrelevant. Since this "test" for sensorless and the hall effect array happen each and every time this would not account for it going the correct way but just at a slow speed. I have seen so many problems with the Spektrum that I would not rule it out but I think it is in the ESC itself or the connections or power supply.

The truth is that you will have to just eliminate one thing at a time.

[SlowOne]

Agree with RURC, you've got a dodgy connection somewhere. Could be a dry solder joint that is being moved with the jolt of the landing, or a poor joint somewhere else.

If the steering is working 100% during the motor problem, it's not likely to be the Spektrum. I'd also do one thing at a time and keep trying. Check all connections - clean, dry and replug - then re-solder the motor wires - try again - then change the sensor wire... you get the picture. If nothing changes, change the receiver and then the speedo.

As it's an LRP, if you can do without it for a fortnight, send it to Horizon with your description above, and ask for a check - you never know... HTH

[DaveG28]

Cheers guys,

Have changed the sensor wire, and if that doesn't fix it will change the motor, then the esc.

[RURC]

Originally Posted by DaveG28

Cheers guys,

Have changed the sensor wire, and if that doesn't fix it will change the motor, then the esc.

I really think that if it was in the motor it would be a permanent problem not on and off. If it was in the motor that would be either an issue with the sensor grid, either a broken off sensor or a not turning array. Either one would be all the time. The only other thing I can see in the motor is a very gaulded bearing. Was the motor very hot? If so this is a possability. But this generally would be all the time

[DaveG28]

The motor was very hot, but then ,ine always run really hot, I am told I am extremely brutal throttle wise!! I've even managed to dump during a run at a regional with 4200 cells and a 5.5 motor!

[RURC]

Originally Posted by DaveG28

The motor was very hot, but then ,ine always run really hot, I am told I am extremely brutal throttle wise!! I've even managed to dump during a run at a regional with 4200 cells and a 5.5 motor!

Are you exceeding 200 F (93 C)? If so you may have a heat related issue in the motor. I really dont know on the LRP motor but 200 is considered the max on all but very top line motors, of which the LRP is not one. None of the run of the mill motors are. Not Novak, Speed Passion, Tekin, or Hacker. For that matter only Plettenberg, Neu, and Lehiner make ones that will take more than that and they are upwards to $400 USD just for the motor and are not sensored.

In the future I suggest you monitor your motor temps and try to keep it as low as possible. Heat is the enemy of power. It causes everything to work harder, even your battery and esc. 160 to 175 is fine. One thing you can do to combat this is change your bearings to ceramic. This will cut your temps. I do this to almost all our team cars.

[DCM]

good point, there is a thermal detector in the motor sensor, but that wouldn't stop it after a jump though, chances are is a problem in the sensor loop.

[niggs98]

might find that due to getting everything hot a few times you have created a dry joint in either the motor or speedo and under heavy impact it is creating an intermitent fault

[DaveG28]

Have thought about whether it could be a dry joint, had a brushed motor with one where it did the cutting out after jumps then coming back alive, but not sure that answers why it then runs out of control?

Also, this is happening very early in the races, although I don't know how quick they hit peak temp?

Still, could well be heat damage I guess, even if not that hot at the time it fails!