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Old 12-24-2004, 07:02 AM   #1
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Default Cobalt motors.

We play with dragsters as well as touring cars, here in Malta, so we are constantly looking for more potent motors.

A while ago I bought a Trinity Cobalt motor - smaller diameter can and costs an arm and a leg. It takes normal size armatures so these are not a problem.

As we have a drag meeting coming up I thought I'd dig this motor out of the box and play a bit. I put a 6 turn arm in, and put it on my Yokomo MMS motor checker. Now a normal 8 x 1 mod motor as we use on our touring cars, will draw a current of say 6 amps - unloaded of course, at 6 volts and will be doing about 40,000 rpm. This cobalt motor doubles that current draw before I can wind the MMS up to anywhere near 6 volts input voltage. So much so that it triggers the "failsafe" on the motor tester - set at about 14 amps draw. It also gets very hot very quickly.

Thinking the 6 turn armature may be the problem I tried it with a 9 turn, with the same results.

Can anybody tell me if this is normal ? Theoretically that sort of amp draw at realtively low revs should give ballistic performance which suits us fine, and the fact that the motor gets hot doesn't matter so much in this application either, because it is only going to run for bursts of between 3 and 4 seconds.

However it seems odd that the cobalt can should draw such high currents. I tried it on my CS motor dyno and as soon as you power up it triggers the fail safe on that too, even with 2 packs of 3300s in parallel.

Any of you motor wizards got any ideas?

Happy Christmas.
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Old 12-24-2004, 07:06 AM   #2
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I'm not a motor wizard, but you might have it shimmed to tight or something is jammed in the motor. It is possible that a brush is touching the base below the comm. Something like that is proablyhappening.
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Old 12-24-2004, 07:21 AM   #3
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No. I'm afraid not. I did think about that and re-shimmed and measured everything up. I even put a meter to it to check continuity in case there was some leakage somewhere, but it all seems right.

Thanks for your suggestions anyway.

Happy Christmas.
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Old 12-24-2004, 07:25 AM   #4
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What was the timing and comm diameter ?
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Old 12-24-2004, 07:36 AM   #5
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Quote:
Originally posted by Fastfreddy74
What was the timing and comm diameter ?
It's a new com. Skimmed once or twice, so it will be about 7.5mm.

I've played with timing from 0 to 6mm advance. The current draw drops off by about 10% at 0 degrees but is still alarmingly high.

Thanks for your input and happy Christmas.
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Old 12-24-2004, 07:43 AM   #6
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Johnbull,

What brushes are you using? You might want to go to a very low silver brush and lighten the spring tension some if you want the motor to pull less amps. Also, these new motors have some serious magnets with plenty of power to spare, you might just have an animal on your hands. LOL! Just my $0.02

Merry, Happy and safe Holiday....
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Old 12-24-2004, 07:53 AM   #7
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I built the motor up with the same brushes and springs we use on our touring cars.

This is why I am so surprised at the difference in current draw.

What I have noticed is that there is much less of a gap between armature and magnets, which could explain some of the current draw, but that much ?
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Old 12-24-2004, 07:56 AM   #8
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I know at cleveland that alot of guys ran the new high silver brush that lasts more runs (sorta like the cs/reedy brush that was run at the worlds in 12th scale), that cost around $15, which i think were included in the motor but not 100% sure. I would suggest trying to hunt down some of those brushes and trying them possibly...
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Old 12-24-2004, 08:00 AM   #9
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Try to set timing at no more than 3-4mm, trinity purple springs and trinity 4380 brushes.

BTW, what's the amp draw at 3.6V?
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Old 12-24-2004, 08:08 AM   #10
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Quote:
Originally posted by Fastfreddy74
Try to set timing at no more than 3-4mm, trinity purple springs and trinity 4380 brushes.

BTW, what's the amp draw at 3.6V?
At 3.6 volts the current draw is already up around 9 or 10 amps, which is far too much.

Hey Freddie. I see you're just up the road from us in Italy !!!!

We hope to make a round of the Italian championship - in Sicily - in 2005. We missed the round at Tre Castagne last year because we didn't know about it.

Do you have any dates for good electric on road meetings in Sicily in 2005 ? I speak to Salvo Mafodda from Catania ocasionally.
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Old 12-24-2004, 08:21 AM   #11
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Unfortunatly next year all major TC events will be held in northern Italy, but if you contact Salvo ([email protected]) he can inform you about their regional championship....

BTW, this year there will be the off-road WC in Collegno (near Turin) even if you don't race off-road i think it's an event you can't miss!

And in 2006 there will be the TC WC in Turin.....

Bye!

Last edited by Fastfreddy74; 12-24-2004 at 08:47 AM.
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Old 12-24-2004, 08:50 AM   #12
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Quote:
Originally posted by johnbull
[B]At 3.6 volts the current draw is already up around 9 or 10 amps, which is far too much.
It seems correct to me, with Nosram Extreme motors i get similar results.....
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Old 12-24-2004, 09:27 AM   #13
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Quote:
Originally posted by johnbull
At 3.6 volts the current draw is already up around 9 or 10 amps, which is far too much.

Hey Freddie. I see you're just up the road from us in Italy !!!!

We hope to make a round of the Italian championship - in Sicily - in 2005. We missed the round at Tre Castagne last year because we didn't know about it.

Do you have any dates for good electric on road meetings in Sicily in 2005 ? I speak to Salvo Mafodda from Catania ocasionally.
Did you check the slots in the comm after you cut it? Are they clean and did you get rid of the sharp edges with a ball point pen?

Nick
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Old 12-24-2004, 11:15 AM   #14
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we had the same problem in our slot car motors when i used to race those. cobalt magnets are a ton stronger than ceramic magnets, also a lot smaller. we would have to sometimes help the motor start out to break it in. spin the arm by hand when turning the power on. especially on low wind motors. i ran group 7 stuff in the 7 or 8 turn area. once we got it going and broken in every thing else fell in line. softer springs will help with amp draw as someone else pointed out. hope this helps, have a great holiday!!!
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Old 12-24-2004, 11:25 AM   #15
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rudedog is right the gauss of the cobalt magnets is by far greater then the ferrite mag motors people use in there tc cars.. this in turn increases the amp draw because of the friction the magnets put on the arm at low voltages...
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