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Old 12-11-2016, 10:45 PM   #226
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Originally Posted by gigaplex View Post
It would be too similar to the 21.5 sportsman class that we run over here, which would likely dilute things a bit.
+1

Some of the USGT rules are looking to be adopted such as the USGT approved body list, and the same tires that USGT use that appear to offer good traction levels over various surfaces.
Some other details have to be sorted out such as min car weight, but getting the "core" rules down on paper is the main focus point at this point in time.
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Old 12-12-2016, 05:53 AM   #227
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Simply replacing with a 17.5 wouldn't change things, but a spec/control 17.5 at fixed timing and FDR (rather than open 21.5) would change things by virtue of everyone being at the same setting. I wouldn't need to worry about finding peak efficiency and monitoring temperatures.

I did some no-load current readings last night using a multimeter plugged into my ESC, and it was drawing around 3A at the original 30 degree timing, and a touch over 6A at 34 degrees timing. I couldn't get to 40 degrees timing without blowing the 10A fuse on my multimeter. I think that's why the motor was overheating, I don't think gearing would have helped much. It's a Reedy Sonic M2.
I really don't follow your logic.

Why can't everybody be at the same setting with 21.5 but they can with 17.5? And why do you think 17.5 motors don't overheat?



That doesn't necessarily explains why the motor doesn't perform.

I suggested you measure the wheel revs because that gives you a more useable information. The current measured means nothing, especially since the motor is driven in AC/impulse. Measuring wheel revs can be then compared to performance on track. If the car doesn't show on the track the speed corresponding to wheel rev, it is clear the motor can't pull the car weight hence no point in persisting with gearing/timing. You can even build a graph of wheel rev unloaded vs loaded, and you'll see the drop off point in the graph where the motor falls off its torque curve.

You might need a partner to time you on a stretch of straight ( you can use a datalogger but you get again in the same problem as with the motor dyno - money, practicality, etc).

I have done the same thing for my cars and short of buying a motor dyno (expensive, clumsy, convoluted to use), I find this is the best way to tune timing and gearing. More reliable too, because it is actually tuned under real track conditions rather than on a bench with a dyno that may or may not give any relevant data.
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Old 12-12-2016, 06:13 AM   #228
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I really don't follow your logic.

Why can't everybody be at the same setting with 21.5 but they can with 17.5? And why do you think 17.5 motors don't overheat?
I never said they can't do that with 21.5. But a 17.5 set up conservatively is going to generate less heat than a 21.5 pushed to the limits. And a 21.5 set up conservatively may be too slow.

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Originally Posted by niznai View Post
That doesn't necessarily explains why the motor doesn't perform.

I suggested you measure the wheel revs because that gives you a more useable information. The current measured means nothing, especially since the motor is driven in AC/impulse. Measuring wheel revs can be then compared to performance on track. If the car doesn't show on the track the speed corresponding to wheel rev, it is clear the motor can't pull the car weight hence no point in persisting with gearing/timing. You can even build a graph of wheel rev unloaded vs loaded, and you'll see the drop off point in the graph where the motor falls off its torque curve.

You might need a partner to time you on a stretch of straight ( you can use a datalogger but you get again in the same problem as with the motor dyno - money, practicality, etc).

I have done the same thing for my cars and short of buying a motor dyno (expensive, clumsy, convoluted to use), I find this is the best way to tune timing and gearing. More reliable too, because it is actually tuned under real track conditions rather than on a bench with a dyno that may or may not give any relevant data.
I've heard from several motor tuners that a no load current test will give some indication of heat generation at load. Setting a no load current of more than 6 amps usually leads to a hot motor. This is just a guideline, but what I was trying to point out was that at the timing they recommended, it was drawing roughly double or more of the recommended current. That's why it got too hot.

I didn't measure the revs like you suggested because it was late at night. I'll do so when I get the opportunity. I've also been contacted by one of the local AARCMCC members who's offered to help me tune my motor next time we're at the track.
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Old 12-12-2016, 06:53 AM   #229
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sorry to skew the topic, but those of you going to snowbirds. Will you be running the new stock(21.5) or the new super stock(17.5) for tc, and what class did you run before?
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Old 12-12-2016, 07:36 AM   #230
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Originally Posted by gigaplex View Post
I never said they can't do that with 21.5. But a 17.5 set up conservatively is going to generate less heat than a 21.5 pushed to the limits. And a 21.5 set up conservatively may be too slow.


I've heard from several motor tuners that a no load current test will give some indication of heat generation at load. Setting a no load current of more than 6 amps usually leads to a hot motor. This is just a guideline, but what I was trying to point out was that at the timing they recommended, it was drawing roughly double or more of the recommended current. That's why it got too hot.

I didn't measure the revs like you suggested because it was late at night. I'll do so when I get the opportunity. I've also been contacted by one of the local AARCMCC members who's offered to help me tune my motor next time we're at the track.

Yeah, I was trying to make sense of your earlier post in context.

A lot of people seem to think that spec racing means slow. It doesn't have to. Of course there will always be people who want to go faster, no matter what the stock class is and that's why there are classes for that too.

A lot of this thread is made up of posts of people having completely different discussions muddled by what everybody understands by spec/stock.


Yeah, current under no load gives some indication. About as vague as trying to estimate how much current your house is going to use when everything is switched on by measuring how much it is using when everything is off.

But you are right, if your motor sucks more than 6A at no load, it will definitely suck more at load.

That said, currents like that are not necessarily a problem. We have speedies that claim they can hold 150A continuous. The question is, what does the motor do with this current? Hopefully not heat.

My point was that these are just indirect indications of what the motor is doing under load, and not very good indications at that. Tuning the motor to get this or that current at no load does not guarantee anything either. You don't know what the power/torque curve of your motor is. Even if you dyno the motor, you only get the results under whatever arbitrary load the dyno manufacturer considered they should apply. That may or may not have anything to do with what your car does on the track.
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Old 12-12-2016, 07:57 AM   #231
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sorry to skew the topic, but those of you going to snowbirds. Will you be running the new stock(21.5) or the new super stock(17.5) for tc, and what class did you run before?
Last yr
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Old 12-12-2016, 12:46 PM   #232
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Yeah, I was trying to make sense of your earlier post in context.

A lot of people seem to think that spec racing means slow. It doesn't have to. Of course there will always be people who want to go faster, no matter what the stock class is and that's why there are classes for that too.

A lot of this thread is made up of posts of people having completely different discussions muddled by what everybody understands by spec/stock.


Yeah, current under no load gives some indication. About as vague as trying to estimate how much current your house is going to use when everything is switched on by measuring how much it is using when everything is off.

But you are right, if your motor sucks more than 6A at no load, it will definitely suck more at load.

That said, currents like that are not necessarily a problem. We have speedies that claim they can hold 150A continuous. The question is, what does the motor do with this current? Hopefully not heat.

My point was that these are just indirect indications of what the motor is doing under load, and not very good indications at that. Tuning the motor to get this or that current at no load does not guarantee anything either. You don't know what the power/torque curve of your motor is. Even if you dyno the motor, you only get the results under whatever arbitrary load the dyno manufacturer considered they should apply. That may or may not have anything to do with what your car does on the track.
You're right about not knowing the power/torque curve etc. However at no load there's essentially no torque, so most of the current pretty much translates to heat. It'll only get worse under load. I think it's mainly used to find the upper bound of timing before efficiency goes out the window, rather than finding peak power.
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Old 12-12-2016, 12:55 PM   #233
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We have 2 similar classes where I race (asphalt). We have 17.5 stock and 21.5 GT. In 21.5 GT, we run 21.5 blinky and have to use a GT body (most run Camaros and Caddies). Funny thing is the 21.5 class is only 1 lap off of 17.5. 28 laps in 17.5 versus 27 in 21.5. Lap times maybe .2 to .3 seconds slower is all. And as far as I'm concerned, the 21.5 class is an easier car to drive, I don't find myself overdriving the car nearly as much.
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Old 12-12-2016, 01:55 PM   #234
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Harder tires. At the speeds we go, downforce is a fairly small number. Downforce is a multiplier, if the "big number" is much smaller, downforce matters less.
I don't agree. Downforce is considerable, try running without a body.

IMO lower downforce bodies and softer tyres would be better. More consistent grip from low to high speed, more grip off the racing line making it easier to pass leading to better racing.

The current bodies are also fragile in the context that minor damage has a significant impact on performance.

The trade off is softer tyres wont last as long.
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Old 12-12-2016, 02:22 PM   #235
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If we change stock to 21.5, we all get to throw our 17.5's in the trash, and then two years down the road we get to have this conversation again about whether 21.5 is too fast we should switch to 25.5, then again in 2 years switch to 35.5, then around 2025 or so we are running 100.5 turn motors and you can walk around the track faster than your car. We would, of course do this for the good of the hobby and getting new racers running without more power than they can handle

Nobody ever talks about skill or talent or how to make slow or out of control drivers faster and better, its all in making some rule about motors. Always arguing that motors are too fast.

Stock is not a beginner class. It never was. When I was a beginner, stock was an expert tier that we lowbies beating ourselves apart in Novice could aspire to.
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Old 12-12-2016, 05:14 PM   #236
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Yep and Mod was the Elite class where the sponsored guys hung out.
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Old 12-12-2016, 05:51 PM   #237
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Originally Posted by gigaplex View Post
I never said they can't do that with 21.5. But a 17.5 set up conservatively is going to generate less heat than a 21.5 pushed to the limits. And a 21.5 set up conservatively may be too slow.
I recall seeing a video somewhere of the junior finals at the recent on road nationals, where I think they were using 21.5 motors set at a certain fdr?

I can't seem to find it, but I know the cars were pretty slow.
*found it*
https://www.youtube.com/watch?v=Obrp...bxeuxLNDF2L8Xy

And yes, also agree about the heat issue, especially during summer racing.
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Last edited by ta04evah; 12-12-2016 at 05:58 PM. Reason: Found video
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Old 12-12-2016, 06:04 PM   #238
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Originally Posted by ta04evah View Post
I recall seeing a video somewhere of the junior finals at the recent on road nationals, where I think they were using 21.5 motors set at a certain fdr?

I can't seem to find it, but I know the cars were pretty slow.
*found it*
https://www.youtube.com/watch?v=Obrp...bxeuxLNDF2L8Xy

And yes, also agree about the heat issue, especially during summer racing.
The winner sat out A3, so here's A2 with the full field:
https://www.youtube.com/watch?v=0CK4Vj2xubw

The concept of a capped FDR for a specific motor is well illustrated here. It was cool to see them all go up the back straight at the same speed.

However, the 4.5 ratio for the TrackStar motor used in this Junior class is way shorter than what could be workable and still safe. FWIW.

Phil.
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Old 12-12-2016, 06:42 PM   #239
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The winner sat out A3, so here's A2 with the full field:
https://www.youtube.com/watch?v=0CK4Vj2xubw

The concept of a capped FDR for a specific motor is well illustrated here. It was cool to see them all go up the back straight at the same speed.

However, the 4.5 ratio for the TrackStar motor used in this Junior class is way shorter than what could be workable and still safe. FWIW.

Phil.
Hence the reasoning behind the choice of a 17.5 motor for the GT class, at moderate gearing, & fixed timing, it's around the same speed as a non fixed fdr 21.5, maybe even a little slower, but it ensures motor longevity, so people are not "temping" their motor to see how far they can push it on any given day, or track.
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Old 12-12-2016, 06:51 PM   #240
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Originally Posted by PDR View Post
The winner sat out A3, so here's A2 with the full field:
https://www.youtube.com/watch?v=0CK4Vj2xubw

The concept of a capped FDR for a specific motor is well illustrated here. It was cool to see them all go up the back straight at the same speed.

However, the 4.5 ratio for the TrackStar motor used in this Junior class is way shorter than what could be workable and still safe. FWIW.

Phil.
They actually looked slower down the main straight in person.

Some of those Juniors stepped up to sportsman last weekend, and were actually pretty quick. Once they get used to the speed and stop over driving it, I'll probably struggle to keep up
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