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Why are 17.5t motors used for stock racing?

Why are 17.5t motors used for stock racing?

Old 03-16-2016, 09:19 PM
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Default Why are 17.5t motors used for stock racing?

Is their KV rating comparable to a well-tuned 27t brushed motor? Do they have comparable power usage as a 27t brushed motor? Or is it just one of those circumstances where it just happened to be widely-available when the rules were being written? Just curious, I know nothing about the history of touring-car racing.
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Old 03-16-2016, 10:45 PM
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I can't speak to the specific reasons why they were chosen, but here's a quote and some info from a post on rcuniverse:

RE: Brushed VS Brushless VS kV - Ratings
Brushless is much more free gearing, so not really. It depends on what you are comparing, top speed, max power, starting torque, efficiency, etc.

The current brushless equivelencies for racing are 27-turn brushed = 17.5 brushless, 19-turn = 13.5 brushless. These are rather conservative on the brushless end, a very well maintained, top-end brushed can beat out a brushless per the comparison above. But this requires meticulous maintainance, like new brushes every race series (3x 5 minute runs) and a comm cut every third race. Brushless generally does have to be geared higher to keep up.

With brushless, there can be huge differences in terms of max power (as much as +25%), starting torque (same), and efficiency between one motor and another, ie. the Hacker E40 and the Novak pre-ballistic motors. Typically this is a tradeoff and there is not one 'perfect' motor that excels at all given traits. Except maybe the really high-end motors like Neus which cost in the $200. plus range. Also, the profile the ESC is set to can have a tremendous effect on the peak power going full-throttle from a dead stop, since with brushless the ESC controls the variable timing advance.

This is similar in concept to the fixed timing advance set with brushed, by rotating the endbell, except that a good variable timing advance profile need not sacrifice efficiency at the lower RPM band.

http://www.rctech.net/forum/electric...less-dyno.html
http://www.rctech.net/forum/electric...al-thread.html

These two links above give dyno test results to verify (experimentally) some of the statements Imade above, like the comparisons of the hacker E40 13.5 and the Novak 13.5 where the Hacker has significantly more starting torque and slightly more max power, the novak has better efficiency.
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Old 03-17-2016, 03:11 AM
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They were originally similar power to a 27t brushed.

With development in motors, Lipos and ESCs, they're probably closer to a 19t brushed now. Which is why some areas have gone to 21.5t as 'stock'.
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Old 03-17-2016, 05:46 AM
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Originally Posted by daleburr View Post
They were originally similar power to a 27t brushed.

With development in motors, Lipos and ESCs, they're probably closer to a 19t brushed now. Which is why some areas have gone to 21.5t as 'stock'.
This. A good 17.5 with a decent lipo is easily as fast as 19T brushed with 6 cell nimh. 21.5 & lipo is about the same speed as "stock" used to be.
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Old 03-17-2016, 07:50 AM
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All motors are stock. They have to be built to a spec and therefore stock. Race promoters and sanctioning bodies dub certain motors a "stock" class, which implies, less than modified. Track size should determine what is stock. As far as comparing top speeds, Dale and Brian are right. Bottom end punch is what most everyone has a hard time with. Brushless is a different world.
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Old 03-17-2016, 10:50 AM
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Default How did 17.5 BL become "Stock"

From way back when:

When brushless motors first start making appearance in RC car racing, the earliest were relatively expensive and clumsy adaptations of motors built for RC aircraft . Same for the ESCs to support them. But many could see their potential. At that time the "standard stock motor" was a 540 sized, 2 pole, brushed motor, with 27 degrees of timing.
The brushless motors offered a increase in reliability with an immense reduction in maintenance requirement. At that time a 27turn motor required frequent (monthly/weekly) brush replacement and frequent (race-daily) commutator "skimming" to keep it competitive.

Eventually Novak came out with the first widely available , reasonably priced brushless motor and ESC system, the "SS". The ESC was huge and had virtually no adjustments. The motor was slightly down on torque compared to a 27turn, but it was way more effecient so your battery remained strong for the entire then 5 min. race .

Novak eventually developed a variety of "winds" (13.5, 10.5)etc for its SS line. Most people found the 13.5BL motor to be roughly equal to the 27T in terms of performance over the period of a race.

As more people start running the SS systems in local/club events, race sanctioners (ROAR) started to think about what a ROAR approved brushless system might become. Others had started Brushless Racing leagues or series.

A faction (notably lead by Trinity) tried to get brushless motors outlawed from ROAR sanctioned events.

ROAR did publish specs for BL motors and invited mfgr submissions. In this initial ROAR adoption of BL motors ROAR did one unexpected and smart thing . 17.5BL was designated as the "27T/stock equivalent" motor. While it was recognized that the then current 17.5s were less powerful than a full race 27t brushless. ROAR rightly bet that BL performance would increase over time and eventually catch the brushed motor. So 17.5 became "STOCK". Now the 17.5s are so powerful that in many places/classes 21.5 BL are becoming the defacto "Stock Class".

Rod
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Old 03-17-2016, 11:48 PM
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Interesting. Thanks for the history lesson.
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Old 03-18-2016, 09:05 AM
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Thanks for the write up Rod!

I've been back into racing competitively for 2 years now, after I stopped racing back in 2007. That was also around the time that Lipos and BL systems, mostly Castle, were becoming popular. I still had all brushed motors and even Nicd's (never used nimh) so I chose to stop racing as I didn't want to replace all of my electronics to be an early adopter of the new brushless/lipo technology.

I missed racing, but when I got back into racing I was utterly blown away by the new brushless motor and lipo battery technology. It's so nice not having to true comms, change brushes, religiously care for your batteries and only use them once per race day. Racing seems much more accessible now, and cheaper! I do agree the 17.5 is now almost as fast as what a brushed mod motor was, but I'm having so much fun and can't wait to give mod a go now.
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Old 03-18-2016, 09:43 AM
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Originally Posted by CamLS View Post
....It's so nice not having to true comms, change brushes, religiously care for your batteries and only use them once per race day. Racing seems much more accessible now, and cheaper!
I agree with you, but a surprising number of people don't

Always amazed at how many people complain about the cost of RC, when it's cheaper than it ever was!
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Old 03-18-2016, 09:55 AM
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Originally Posted by Skiddins View Post
I agree with you, but a surprising number of people don't

Always amazed at how many people complain about the cost of RC, when it's cheaper than it ever was!
Something something...instant gratification...something....

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Old 03-18-2016, 09:56 AM
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Default increased TC performance

Camls/Fyrstormer,

Yes, todays "17.5/Stock" Touring cars have become a fast as "MOD" was 10 years ago. Much but not all of the performance increase is down to the newer/better motors. A couple of things have also changed.

[B]Battery[/B ]Roughly concurrent with the adoption of Brushless Motors came the Lipo battery revolution which displaced the Nicad and Nimh power packs. Again the RC airplane guys were "early adopters" and it took RC car racers a couple of years to catch up. There were a couple of false starts while standards were worked out as to battery size, voltage, hard vs soft cases, connectors etc.
Like the early BL motors, the early lipos were down on punch. But they had consistency, required less "care and feeding", and could be cycled more frequently and had a longer "useful lifespan" than a Nimh. As a bonus, the Lipo weighed significantly less than an equivalent Nimh of the same Mah capacity. Until the Minimum Weight limits were lowered, Lipo powered TCs had to carry significant additional weights to "make weight" at ROAR/IFMAR sanctioned events.

Weight It took a while, but the sanctioning bodies eventually caught up with the BL/Lipo facts on the ground and reduced minimum weight requirements. Today's high end TCs run at a weight 100-150 grams lower than their older counter parts. Weight reduction is generally a good thing for race cars. Faster acceleration/deaccleration, lower tire wear, less drive train wear and tear and reduced power consumption are all by products of lowering weight .

Chassis Design The designers have made continuous, incremental changes over the past several year. No one element has been revolutionary,
and very few of the changes really require a name nomenclature change to highlight a "new optimized 20xx version", but the little changes add up over time. An Associated TC5 may look greatly like a TC7 to the uneducated eye. They're both pretty much standard touring car design. Carbon fibre and aluminium materiels, 2 belt drive, eletrics down one side battery on the other like 90 per cent of the other TCs on the market. But I can't think of very many parts of the two cars that are interchangable. All the components have been replaced, changed and tweaked over time. As a result the newer car is lighter, carries more corner speed and is easier to drive fast than the old. Most of the other "Name" mfgrs (Yokomo, Xray etc) have followed a similar evolutionary path.

In addition to more reliable, less maintenance intense motors, today's TC have more battery power to drive, lighter cars with better handling chassis.

So the whole "package" turns in faster lap times.

Rod
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Old 03-18-2016, 06:23 PM
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Originally Posted by Buffalo 16 View Post
Camls/Fyrstormer,

Rod
Good to hear from you ROD!

If you can, check the TCS motor thread: 25.5-turn motor pulling 11 amps
any comments?
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Old 03-18-2016, 07:09 PM
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Originally Posted by Skiddins View Post
I agree with you, but a surprising number of people don't

Always amazed at how many people complain about the cost of RC, when it's cheaper than it ever was!
I would only race brushless nowadays, but for bashing, brushed motors still have some appeal. They make fun noises, they run as smoothly as the smoothest sensored-brushless motor, and they cost a lot less. And of course, for crawling purposes, brushed motors don't care about getting wet, which makes them easier to run in wet conditions -- no waterproofing necessary. Yes, they lose some performance with each run until they're taken apart and lathed, but that only matters when racing. To me they're sort of the electric equivalent of an old carbureted engine compared to a new fuel-injected engine -- yes, the new fuel-injected engine is more reliable and more powerful, but the old carbureted engine has more to tinker with, and responds in very obvious ways to simple adjustments.
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Old 03-21-2016, 02:09 PM
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about 9 years ago, i lived in the midwest. carpet oval racers were really fast in incorporating Novak brushless motors into their races and providing key feedback.

btw...it was also carpet oval racers to test and embrace Lipos, adjusting rules, independent of ROAR. they were the reason you see 1S lipos in pan cars because 2S was deemed too fast. very few tracks allowed lipos, with serious rules considering the hazards

Novak information at the time basiclly...more or less...touted the 13.5 as a 27T brushed replacement, more consistent, more equal, etc. they had info out that they tested top% 27T brushed motors and 13.5 was deemed as equal.

carpet oval racers were predominately using 4-cell nimh with 10.5 and 13.5, as they figured out gearing, optional rotors, and set-ups, within the first year started asking for 17.5. at the main track i raced 27T and 19T records were being smashed in first months of the SS ed. 13.5/10.5 BL motors. eventually 17.5 was made the new stock for pancar oval

i decided to try it onroad, so i bought a GTB and 13.5 SS, put it in a HB TC-Cyclone, i went to a loose rule track, that raced 27t, 19t, and gas TC classes on asphalt. i entered 27T stock which i usually ran. after 1st qual they moved me to 19T which i won. next time i showed they put me with nitro. i was not faster on straights, but faster thru their infield more consistent and won.

i remember the war of words back them on BL and Ernie Provetti's open letter in RC Car Action back in 2006/7 concerning BL coming into the RC industry, concerning what will happen, costs, etc. he was flamed by many as trying to keep his dominance in the 27T brushed motor empire, he would lose money/business, etc. he countered that he would adapt, but continued with various predictions.

long story short....if you read the open letter......EP was right

9 years ago i was paying around $80 for top brand mod motors for my 12th scale, in the $40-50 zone for ROAR legal 27T's for my TC

now for 1/10 scale, i see mail order online top brand BL mod motors $90-120 zone, a see top 17.5 brand stock motors in the $90-150 zone. the 149.99 17.5's are top 5% motors.

imo the current state of the 17.5 stock may need to be looked at by ROAR, and adjust to 21.5 or 25.5.

Last edited by fast-ho-cars; 03-21-2016 at 03:29 PM. Reason: my ROAR.....by ROAR
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Old 03-21-2016, 02:49 PM
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Originally Posted by fast-ho-cars View Post

9 years ago i was paying around $80 for top brand mod motors for my 12th scale, in the $40-50 zone for ROAR legal 27T's for my TC

now for 1/10 scale, i see mail order online top brand BL mod motors $90-120 zone, a see top 17.5 brand stock motors in the $90-150 zone. the 149.99 17.5's are top 5% motors.

imo the current state of the 17.5 stock may need to be looked at my ROAR, and adjust to 21.5 or 25.5.

There are amazingly capable mod motors still around the $80-95 mark - Look at the Reedy M3's.

Stock motors are around the same price.

I agree, stock needs to move to a 21.5.
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