Aahj

iTrader: (6)

Hello,

I have a Tekin RS in my SC10. It's boosted with a 17.5T brushless motor and have an issue with the brakes. No matter what brake strength I set on the ESC, it doesn't seem to change at all. It always feels like it's on the lowest setting. It requires me to brake extremely early for corners. Any suggestions?

Thanks in advance for any and all input!

AJ

Bubblehead

What's the best way to determine start and end RPM's? If the layout was 45' x 96', motor 17.5.

HarryLeach

When I'm starting a profile from scratch, I use the rough kV to figure out where I want my RPM range.

For 17.5 I take 2400 * 7.2 [you can use the battery ending voltage if you think your profile is pretty close, otherwise I use nominal voltage] = 17,280.

You can use this for your end RPM, but I usually knock around 1k RPM off that figure, so call the end RPM 16,000.

For start RPM, I usually set it for the top 60% so 16,000 *.4 [take 40% off] = 6400. Pick something close from the list of calculated Start RPM values.

After that, it's just a matter of fine tuning to preference. If you want more pull off the corner, raise the Start RPM up about 1,000 RPM. If you want to smooth out power deliver on bottom end, lower the Start RPM about 1,000 RPM. Repeat as necessary.

The amount of boost you run is gearing dependent, for 17.5 at DRCW, I'm usually around 6.3FDR for carpet and asphalt, and run 45-50 Boost.

I only use Turbo if I'm visibly lacking in straight away speed, and don't think the added speed is going to hurt corner entry at the end of the straights. The most Turbo I'll run is around 10, ramp 1 or 2, with .4 delay [almost always]. I don't remember if I was running any today or not.

You could've asked this at the track today


EDIT: Forgot to mention, if you feel like you want mid-throttle acceleration snappier, lower the End RPM down 1000 RPM at a time until you're happy. If you feel like mid-throttle acceleration is too aggressive, drop the Boost down in increments of 5.

To me, if you see the car kind of "shifting gears", your profile is likely going to upset the car and make it needlessly hard to drive, and slower. I'd rather see the car accelerate smoothly, but very quickly instead.

I do pretty well the same thing for 1s 1/12th, just recalculate as above for half the voltage.

FYI: I use 3400 kv as my rough estimate for 13.5, and 4200 kv for 10.5's. Every company's motor is a little different, but the above calculations have served me well when building a boosted profile.

Bubblehead

Harry, I have asked a few people at the track you are the only one to explained it that way. It seems people keep more secrets with brushless motors /ESC then when racing brushed motors.

Thanks for the info.

HarryLeach

Most of the ones I can think of that would be keeping secrets at the track have gotten setup help from me. I'll explain anything you want, and I think I've gotten pretty good at providing people with more power than they can handle.

rai

Hello,

Need some opinions on this matter (helping a friend on his used rs pro). Before that here's the esc setup.

Turbo ramp - 0.2
turbo delay - 0.04
turbo timing - 13
start rpm - 1600
end rpm - 13500
boost timing 50
profile 4
neutral width 18

Motor used - Hobbywing 8.5 T
FDR - 8.08

The problem was the motor /esc went sensorless after 3-4 mins run. Tested the car it was fine for the first 3-4 mins with turbo kicking but after that it went sensorless. Changed everything to find the problem such as changing the sensored wire (2 -3 wires), changed the batteries, calibrated the radio with the esc, well, almost everything that we can think of. Every input has the same result. The surrounding temperature was 35-40 degree C. Motor temp after those run was 65-69 degree C. Esc LED temp lit at only 3. So what is the problem actually?

HarryLeach

For one, that's a lot of timing on an 8.5.

What is the start RPM?

Do the sensors check out? Should be able to roll the motor over slowly and see a sequence of 3 half-lit LEDs indicating which sensors are reading.

rai

Oh sorry about that Harry, it's 8.08 fdr with start rpm 1600. And yes, we did checked the sensor wire. He's running for modified class in our local race. What about changing the fdr to 7.78 with turbo timing 20 and boost timing 50? We have a 45 m long straight track with two sweepers and technical infield.

HarryLeach

So it runs fine for 3-4 minutes, then goes sensorless?

Have you checked the motor temp when it drops into sensorless? Could be a motor temp issue causing sensors to drop out.

Have you tried a different motor?

Have you raised the throttle EPA up 5-10 points after calibration?



For an 8.5 I would run the End RPM at 25,000RPM and the start RPM around 11,000RPM [or lower] as a starting point, but check those other items first before you start messing with the profile. No sense changing things if it's an equipment issue. If it's a heating issue, a broader RPM range should help.

Randy_Pike

iTrader: (6)

What radio system is he using? This is a lot of boost for an 8.5 but if the batteries and motor can take it, it should work. I also don't care for 0 delay on the turbo. This is likely causing a low end bog. Raise it to .3 and I bet his lap times come down.

rai

Motor temp was 65 - 69 degree just as it went sensorless. Havent tried on different motor yet. Will be doing that tomorrow hopefully. And we didnt tried raising the EPA after calibration. We will check this out first then try the rest. Thanks Harry..

rai

He is using 4PK radio system. Ok, will try to raise the delay to .3.
Thanks Randy.

Bubblehead

I think I'm starting to understand, start/end rpm determines how much timing will be applied per 1000 rpms, if starting rpm stays the same and end rpm increase less timnig will be applied per 1000 rpms.

If I had 50* of timing and a difference of 10, I would have 5* of timing per 1000 rpms

If I changed the difference to 11, I would have 4.5* of timing per 1000 rpms and torque would increase?

Turbo kicks in at a selected time (delay) and adds timing at that point, Ramp determines the rate of applying turbo (1, .5, .3 sec).

If that is correct, what difference would I see if start rpm was 5000 end 15000 and I changed start/end to 3000/13000?

Randy_Pike

iTrader: (6)

Yup, you've got it.

The lower rpm ranges the low and mid range will be stronger.

HarryLeach

What I've found in testing, moving the entire range down can sometimes smooth out throttle feel, but also add heat to the motor, while keping the same top speed.

I try to set the start RPM as low as I can with no bogging, rubber band like acceleration, or dead spots, which is why I use the 60% rule (boost only applied during the top 60% of the no-boost RPM range). The motor will turn more RPM than your end RPM setting, but an RPM range too narrow adds heat without acceleration gains, and a range too broad may not acually ever apply all the boost you've specified.

To me if you like the feel of boost on a 17.5 below 6-8000 RPM, you sould use motor timing. I have the calculations somewhere on my computer, but bringing boost in around 6000 is something surprising like 8mph on a 6.3FDR, which can happen within 6 ft of corner exit. Not sure there is much to gain by going lower. Going too high on start RPM can hurt by not accelerating hard off the corner, and then taking off like someone rearended your car , makes the car more unpredictable to say the least.