Sintered rotor unstable at low speeds? Normal?
 

I've got an X11 5.5 sintered motor here and a 2007 Sphere.

I've had this problem where the car seems to stop every so often for no apparent reason.

I've just got the motor out of the car but all connected and at low RPM the motor speed is unstable. I'm doing this by setting the drive ratio to say 5% on the transmitter.

You can clearly hear it juddering and speeding up and down. Sometimes it even momentarily stops - like for a fraction of a second. Is this normal?

I don't have this issue with a bonded rotor - the one that originally came with the X11 motor. I've tested tonight and compared the two and the bonded one is fine.

ESC settings are set to, ADPC number 3, 0 initial brake and 0 auto brake. The ADPC makes light difference when set lower, but the motor still exhibits this strange behaviour.

Any ideas? Thanks.

If its fine with one motor, but changing to another you have a problem, I would suggest its sensor problem with the new motor.

Maybe you can prove it by swoping the bonded rotor into the can of the sintered motor?

I only have one can, this originally had a bonded 5.5 in it. This spins fine and I have proven this today.

I bought a sintered rotor to go in the same can - this spins up / down / stutters / judders at a range of speeds except flat out, where it spins at a constant RPM (based on the sound alone).

When i put a sintered rotor in my Nosram (6.5) i noticed it cogged a bit at really low power when out the car. Definetly more than the bonded did, But over about 10% it was spinning smooth. So yeah at 5% throttle i reckon the studdering is normal as its a low power and the software is just having trouble keeping up with the rotor is and thinks it should be maybe!

How hot was it when it came off russ? i reckon you had it undergeared and something was thermalling, maybe motor, you only had a 16tooth on didnt you?

I went up about 3 teeth when i put the Sintered rotor in as i could hear it over-revving and it got hot quick. The Durga is geared about 1:9.5 final ratio.

Well I did have a 16T (someone gave me advice of 1 tooth less than bonded) - now it has a 19T. It wasn't that hot coming off though.

I have tested the motor (with sintered rotor) inside and outside of the car. Obviously seems worse when in the car. Shocking the way the wheels stop and start at low RPM's.

So you reckon it's normal. Could be.

It is a big biffing magnet on the sintered rotor and takes some effort to turn compared to the bonded rotor. Maybe it is as it should be.

I'm running it at Bury next week (fingers crossed that there are others there!) so we'll see then I guess.

if the motor has been run a bit, I would look at dismantling as much and give the endbell a thorough flush through, as if there is dirt on the Hal sensor, it can give aratic readings on low end, otherwise it is the ESC not reading rotor position correctly.

Would normal motor spray be okay for flushing out?

yes, that is what I have used.

Don't forget to re-oil the bearings.

Is it the 14mm (green in colour, comes in the latest X-tec motors) sinterd rotor by any chance?

My 14mm's do what you describe in all my motors, you should find the 12.5 and 13mm rotors are fine ;)

I'm not sure if its a speedo software problem or something to do with the 14mm rotor being origonally intended to be used in the 4.5. Mine have never 'just stopped' though, but you do seem to get cogging at very low RPM.

I would have to agree with Rich on this,

the big 14mm rotors are not designed to give smooth power deliver, they are about raw torque.

I prefer the smaller (12.5mm) rotors in both 2WD and 4WD off-road, its almost like the sintered equiv of the bonded rotor, but the reliablility of sintered.

i get that effect on my 14mm sintered rotor as well, i just thought i had a dirty sensor wire :o.

Anyone tried the 12.3mm (or is it 12.2mm) out of the stock spec motors?

G

I think its 12.3mm, but they were out of stock when I asked for one for the EPR national, didn't bother asking again, I do like the 12.5mm very much!

Thanks for this info Rich.

Just checked the LRP website and it is definitely the 14mm one. SKU: LRP50610.

http://www.lrp.cc/en/products/electr...140mm/details/

Well...that solves that one then! :) Now I need a different can. Can you buy these individually?

Either that or a shorter rotor.

what car do you want to run it in and how fast do you want it to go?

if its for racing in 4WD - 5.5 with a 12.5mm would be great
if its for racing in 2WD - 6.5 with a 12.5mm would be great (maybe 7.5 depending on how fast you want to go)
if its for bashing, in 2WD or 4WD, go for a 3.0 with a 12.5mm to get more rpm than you even thought imagineable :thumbsup: - thats what im going to be using at southport then :drool:

Well I just have my 5.5 can with a bonded rotor which is plenty fast enough for everywhere. I just use it for 4WD. I still use brushed for 2WD. Works fine - especially with a LIPO.

I just wanted the sintered rotor so my brakes would be better - I do use and want these.

Thanks for the advice...I'll be getting a 12.5mm one at some point. SKU: 50611.

A wise decision :)

I run the 13mm rotor in my 4wd, although I cant tell too much difference between the 12.5 and 13mm tbh :lol:

sounds good Fiddy.

I have run the 13mm in a 5.5 in my 4WD, but liked the more rpm from the 12.5mm better.