Motor Question

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TRX-1-3
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Motor Question

Post by TRX-1-3 » Wed Apr 19, 2017 2:05 am

Would anyone have any ideas on the brushed "equivalent" to a 10.5 brushless?
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RC10th
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Re: Motor Question

Post by RC10th » Wed Apr 19, 2017 6:08 am

As a guess with static timing....

3.5 = 6t (possibly faster then ever available in brushed)
4.5 = 8t (borderline faster then anything brushed)
5.5 = 10t
6.5 = 12t
8.5 = 14t
10.5 = 17t
13.5 = 19t
17.5 = 21t
21.5 = 27t
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Re: Motor Question

Post by Lonestar » Wed Apr 19, 2017 8:37 am

RC10th wrote:
Wed Apr 19, 2017 6:08 am
As a guess with static timing....

3.5 = 6t (possibly faster then ever available in brushed)
4.5 = 8t (borderline faster then anything brushed)
5.5 = 10t
6.5 = 12t
8.5 = 14t
10.5 = 17t
13.5 = 19t
17.5 = 21t
21.5 = 27t
yup looks about right to me :)

remember than timing can change that tremendously... a properly boosted 13.5 is about faster than a brilliant 12x2 from bitd!
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TRX-1-3
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Re: Motor Question

Post by TRX-1-3 » Thu Apr 20, 2017 4:25 am

Thanks for the breakdown on the motor translation.

Now I rrrrrrrreally want to commission a 17×2 reverse rotation 540 from Holmes Hobbies.
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Lonestar
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Re: Motor Question

Post by Lonestar » Thu Apr 20, 2017 7:53 am

TRX-1-3 wrote:
Thu Apr 20, 2017 4:25 am
Now I rrrrrrrreally want to commission a 17×2 reverse rotation 540 from Holmes Hobbies.
didn't know them and just checked them out. What is so special about their products to warrant such high prices?!? And why go brushed in a modern car when more performance and less maintenance for similar money is available from a BL solution - what am I missing?

Thanks!
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RC10th
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Re: Motor Question

Post by RC10th » Thu Apr 20, 2017 3:15 pm

In the old days reverse rotation just meant turning the endbell 180* , only the fixed timing motors had to be reverse rotation.
Lonestar wrote:
Thu Apr 20, 2017 7:53 am
TRX-1-3 wrote:
Thu Apr 20, 2017 4:25 am
Now I rrrrrrrreally want to commission a 17×2 reverse rotation 540 from Holmes Hobbies.
And why go brushed in a modern car when more performance and less maintenance for similar money is available from a BL solution
Agreed, there are much better BL options out there for similar money. Brushless is far more efficient and requires basically no maintenance. After about 3 - 5 runs your brushed motor starts to fade off untill you give it some love.

The only time I can see a brushed motor being a benefit would be for a crawler if you didn't want to splash out for a sensored set up.
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Re: Motor Question

Post by slotcarrod » Thu Apr 20, 2017 4:34 pm

RC10th wrote:
Wed Apr 19, 2017 6:08 am
As a guess with static timing....

3.5 = 6t (possibly faster then ever available in brushed)
4.5 = 8t (borderline faster then anything brushed)
5.5 = 10t
6.5 = 12t
8.5 = 14t
10.5 = 17t
13.5 = 19t
17.5 = 21t
21.5 = 27t
I think these numbers are very inflated. With zero esc timing and 20-30 motor timing on a 10.5 it would be closer to a 12turn brushed IMO!
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Lonestar
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Re: Motor Question

Post by Lonestar » Thu Apr 20, 2017 7:18 pm

slotcarrod wrote:
Thu Apr 20, 2017 4:34 pm
RC10th wrote:
Wed Apr 19, 2017 6:08 am
As a guess with static timing....

3.5 = 6t (possibly faster then ever available in brushed)
4.5 = 8t (borderline faster then anything brushed)
5.5 = 10t
6.5 = 12t
8.5 = 14t
10.5 = 17t
13.5 = 19t
17.5 = 21t
21.5 = 27t
I think these numbers are very inflated. With zero esc timing and 20-30 motor timing on a 10.5 it would be closer to a 12turn brushed IMO!
I think the "equivalence" chart above is about right at zero esc timing, zero motor timing...

i've ran 12x2 and 10.5T blinky and 10.5T boosted on the same DTM EP track within a couple of years... 10.5T boosted is already faster than most people can handle and feels close to 10-turn-ish or so... 10.5T blinky is fast but because you gear it (and time the endbell) to the moon to squeeze the tiniest bit of power left, but it's sluggish out of the corners (gearing ratio). 13.5T boosted feels like 12-turn-ish.

It's really really hard to make "equivalence" charts as we've had such battery improvements in the meantime, too...

The above feels about right to me :)
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Re: Motor Question

Post by Coelacanth » Thu Apr 20, 2017 11:04 pm

I think the only way you can compare brushless vs. brushed motors is to go by RPM. Number of turns doesn't directly correlate with how fast a motor spins, but kV ratings do. A 3000 kV motor will spin at around 22,200 RPM at 7.4V. You'd need a motor dyno to test actual RPM of a brushed motor, but you can find charts with pretty accurate estimates for vintage brushed motors...like the Kyosho one. The fastest Le Mans motors back in the day--the 240SB and the SPA 240WS--barely broke 30,000 RPM, which was considered very powerful back then. Any current brushless motor over 4000 kV will be in that range or better...and that's not even very powerful by modern brushless standards.

A motor that spins more than 35,000 RPM, all else being equal, spins the tires more times per minute than just about anything vintage...regardless of the estimated "T" rating. 8)

Le Mans Motor Specs_B.jpg
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Lonestar
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Re: Motor Question

Post by Lonestar » Fri Apr 21, 2017 9:58 am

Coelacanth wrote:
Thu Apr 20, 2017 11:04 pm
I think the only way you can compare brushless vs. brushed motors is to go by RPM. Number of turns doesn't directly correlate with how fast a motor spins, but kV ratings do. A 3000 kV motor will spin at around 22,200 RPM at 7.4V. You'd need a motor dyno to test actual RPM of a brushed motor, but you can find charts with pretty accurate estimates for vintage brushed motors...like the Kyosho one. The fastest Le Mans motors back in the day--the 240SB and the SPA 240WS--barely broke 30,000 RPM, which was considered very powerful back then. Any current brushless motor over 4000 kV will be in that range or better...and that's not even very powerful by modern brushless standards.

A motor that spins more than 35,000 RPM, all else being equal, spins the tires more times per minute than just about anything vintage...regardless of the estimated "T" rating. 8)


Le Mans Motor Specs_B.jpg
BL's torque means you can gear them much, MUCH higher. So while 30krpm and 4000kv might look about similar on paper, it feels very different in the track with a totally different fdr. That's without even getting into static and dynamic BL timing, let alone discuss whether those rpm numbers (be they brushed or kV*V) are even reached on the track...

Nice Le Mans chart no matter what :)
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Re: Motor Question

Post by EvolutionRevolution » Sat Apr 22, 2017 9:43 am

IIRC, in my old club's club racing series they switched from a 19 turns "stock" motor to a 10.5 turn brushless because they were considered equivalent.

I put the "stock" between quote marks because the stock motor in question was Corally's machine-wound 19 turns stock motor, which had a RPM of 33,000 or so (so it was faster than quite a few modifieds with less turns). :lol:

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Re: Motor Question

Post by tamiya » Sat Apr 22, 2017 1:33 pm

RC10th wrote:
Thu Apr 20, 2017 3:15 pm
In the old days reverse rotation just meant turning the endbell 180* , only the fixed timing motors had to be reverse rotation.
No, you mean. ZERO advance timing motor... then flipping end bell 180 is only the same as switching the leads over.

If your motor has advanced timing, you need to advance it equally over the other side of zero mark.

BiTD some RCs like ClodBuster needed a matched mirror pair of motors; Trinity Monster Horsepower were offered in mirror pairs.

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RC10th
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Re: Motor Question

Post by RC10th » Sat Apr 22, 2017 2:05 pm

Yes, I over simplified it, but as long as the timing is advanced the same on both motors your fine.
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