Dissimilar voltage required to spin similar motors

[SkaldidDog]

I have two HH45T crawler motors. The brushes are only 30% worn on both motors and the comms look comparable (color and texture). The timings are identical according to the marks on the cans. Caps all appear to be in good shape/are still in place. I cleaned both motors and oiled all bearings. I then placed the good motor on a variable DC supply with V and A readouts. The good motor starts to turn at 0.25V and spins relatively smoothly with some minor stutters. At 12V it draws 6-7A. The bad motor starts to turn at 0.65A and spins roughly (jumpy starting and stopping) until I dial up the voltage to 0.85V then it spins freely. It draws 7-7.5A at 12V.

What could be the source of the differences in drivability (V required to spin smoothly) between the motors?

Thanks in advance for taking your time to respond.

[EddieO]

Well, without being able to trouble shoot them myself....I would first say, replace the brushes.......30% gone is 1/3 of the brush almost, thats too much. Not only is the brush pretty short by then, the comm is probably not looking too fabulous is 1/3 of the brush wore on it without being cut. Also consider that a brush that short, is losing a lot of spring tension, which will effect your drag brake/holding power.

Do make sure the little heatsink screws are not loose, as if they are....the brush eyelet is not making full contact....but as you crank the voltage it jumps and does...

So, I would suggest getting the comm cut and installing new brushes.....break them in at 3 volts for at least 5 min or until fully seated (even wear across the entire brush face).......then see how they work.

If the problem still is there, then you have an issue with the arm more than likely.

Later EddieO

[EeePee]

Originally Posted by SkaldidDog

The timings are identical according to the marks on the cans.

Is the timing set the same (both counterclockwise for example), but you spin one the other direction?

[rock hard]

Originally Posted by SkaldidDog

I have two HH45T crawler motors. The brushes are only 30% worn on both motors and the comms look comparable (color and texture). The timings are identical according to the marks on the cans. Caps all appear to be in good shape/are still in place. I cleaned both motors and oiled all bearings. I then placed the good motor on a variable DC supply with V and A readouts. The good motor starts to turn at 0.25V and spins relatively smoothly with some minor stutters. At 12V it draws 6-7A. The bad motor starts to turn at 0.65A and spins roughly (jumpy starting and stopping) until I dial up the voltage to 0.85V then it spins freely. It draws 7-7.5A at 12V.

What could be the source of the differences in drivability (V required to spin smoothly) between the motors?

Thanks in advance for taking your time to respond.

this may be your problem.

[SkaldidDog]

Originally Posted by EddieO

Well, without being able to trouble shoot them myself....I would first say, replace the brushes.......30% gone is 1/3 of the brush almost, thats too much. Not only is the brush pretty short by then, the comm is probably not looking too fabulous is 1/3 of the brush wore on it without being cut. Also consider that a brush that short, is losing a lot of spring tension, which will effect your drag brake/holding power.

Do make sure the little heatsink screws are not loose, as if they are....the brush eyelet is not making full contact....but as you crank the voltage it jumps and does...

So, I would suggest getting the comm cut and installing new brushes.....break them in at 3 volts for at least 5 min or until fully seated (even wear across the entire brush face).......then see how they work.

If the problem still is there, then you have an issue with the arm more than likely.

Later EddieO

Thanks Eddie. I'll check the screws and try new brushes. I agree they need to be turned.

[SkaldidDog]

Originally Posted by EeePee

Is the timing set the same (both counterclockwise for example), but you spin one the other direction?

They are timed forward in opposite directions since they are spinning as such.

[motorman]

Make sure the commutator slots are clean, if two of the bars are shorted it will be jerky at low v and never get up to full speed.

[SkaldidDog]

Originally Posted by motorman

Make sure the commutator slots are clean, if two of the bars are shorted it will be jerky at low v and never get up to full speed.

Ah. I've not check that yet. Will do.

Cheers.

[SkaldidDog]

Comm spaces were clean but the comms are deeply grooved. Brushes are still nice and tight. New motors on the way.

[JohnRobHolmes]

How long have you been running them? If the comm is deeply grooved, sounds like they have been run a long time! Standup or laydown brushes?

[whoodie]

Yeah definitely cut the comm and replace the brushes on both motors. Also make sure that you're breaking in the brushes in the correct direction that the motor will run, i.e. one motor spins in the opposite direction on an MOA. Getting two motors exactly identical is hard, but not impossible. Keep hammering away at it and eliminate any variables. You'll figure it out. If you can't send them my way, I'll dyno them

[SkaldidDog]

Originally Posted by JohnRobHolmes

How long have you been running them? If the comm is deeply grooved, sounds like they have been run a long time! Standup or laydown brushes?

Since Dec09. Standups (standard?). New motors (HH45s) require only 0.25V to spin and draw about 1.15A at zero and I adjusted timing forward to 1.27A. I made sure to advance the timing (not retard it) by making sure the motors sped up slightly as I changed cap position. I ignored the markings and let the 10% A draw over zero determine the cap position. They sure are smooth. Love the milled brushes. Really nice motors JRH.

[SkaldidDog]

Originally Posted by whoodie

Yeah definitely cut the comm and replace the brushes on both motors. Also make sure that you're breaking in the brushes in the correct direction that the motor will run, i.e. one motor spins in the opposite direction on an MOA. Getting two motors exactly identical is hard, but not impossible. Keep hammering away at it and eliminate any variables. You'll figure it out. If you can't send them my way, I'll dyno them

Thanks for the offer Whoodie. Let me see if I can revive them before I bother you with them. Other than Hudy, who makes a good comm lathe in your opinion. I've done a bit of research but every company touts theirs as best.

Cheers,

[EddieO]

Most comm lathes work fine....the biggest issue is making sure the blocks are square so you are not cutting the comm into a cone.

Xipp/Integy lathes are not bad, but you gotta make sure they squared up...a lot of them out there are screwed up beyond repair.

Good lathes from other companies

Reedy (good luck finding one)
Trinity
Cobra
Fantom (best lathe made)
HARD Racing
Hudy

RCtech or hobbytalk are good places to find used lathes cheap....racers are basically just giving them away.

Later EddieO

[SkaldidDog]

Thanks EddieO. Very helpful.