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Tamiya Super Stock motors with opposite personalities?

Tamiya Super Stock motors with opposite personalities?

Old 02-24-2018, 04:39 PM
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Default Tamiya Super Stock motors with opposite personalities?

Having built an FF03 that I had in my garage for over a year and not having any brushless electronics to put in it, I threw in an old Intellispeed 12T esc and a Mabuchi silver can. But rummaging through the old brushed equipment, I found my Super Stock BZ and RZ motors. I thought I'd test them out and maybe throw one in instead.

Now the BZ had a rough life in a TA02 rally car that did a lot of running in the dirt and snow. Its brushes are pretty shot. Not surprisingly, its max rpm under no load was around 22-23k, well below its 26,500 rpm it should have when new.

The RZ motor was barely used in a TT01 before being replaced with a brushless system (and which is now running a four-slot silver can again). Its brushes still look in pretty good shape. Under no load, using the same esc and battery to test, its rpms were ranging between 30-33k... well ABOVE the 27,500 rpm it should have.

Now my first thought was, "great, this is a hot motor!" Unfortunately, that was literally true too. After around ten to fifteen seconds of no-load running, I felt the motor already getting warm. After letting it run a little longer (another thirty seconds or so), it started getting hot in my hand.

Now what could cause a brushed motor to run so far beyond its specs, while grenading itself? I'd like to use it in the FF03, but I don't need a meltdown...
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Old 02-24-2018, 09:45 PM
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What voltage were you running at? Lipos have higher voltage than the 7.2V nominal that old brushed motors were tested at.
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Old 02-25-2018, 01:13 AM
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I was testing with a lipo battery. I checked its voltage and it was rather low, at 7.6 volts. That's about 5.5 percent higher than the 7.2 volts the motor is used to, but adding that percentage to the 27,500rpm is around 29k. That's closer to the max rpms I was getting, but still below.

I do have an old nimh battery around that should be able to hold a charge. Perhaps I will retest the motors with that plugged in.
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Old 02-25-2018, 03:37 AM
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Originally Posted by longuylander View Post
I was testing with a lipo battery. I checked its voltage and it was rather low, at 7.6 volts. That's about 5.5 percent higher than the 7.2 volts the motor is used to, but adding that percentage to the 27,500rpm is around 29k. That's closer to the max rpms I was getting, but still below.

I do have an old nimh battery around that should be able to hold a charge. Perhaps I will retest the motors with that plugged in.
It's possible the magnets have lost some strength. Symptoms usually are higher RPM but lower torque.
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Old 02-25-2018, 01:57 PM
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With that thought of weakened magnets, I tried swapping rotors and end bells in the motors. With the BZ rotor and end bell in the RZ can, the rpms were about equal at 23k. The RZ rotor and end bell in the BZ can was producing a more reasonable 27k rpm.

Strangely, upon switching them back... they stayed at those speeds! the BZ is still running slow with its worn brushes, but the RZ stayed around 27k rpm and didn't heat up nearly as quickly as it did earlier. This was all using a lipo still; I never got around to cycling that nimh battery.

I'm confused by the motor's performance, but at least I feel more comfortable about testing it in a car and not having to worry about it going nuclear. Once it stops this multi-day deluge, maybe I'll be able to test it.

Thanks for the input!
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