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Speed Calculator
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jcflyer
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Speed Calculator - 09.06.2016, 10:49 AM

I used the speed calculator when I was setting up my truck, and now that it is done I am seeing a near 10 mph difference in what the calculator showed vs the actual mph. Can anyone offer some advice as to why?
   
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ruudxd
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09.06.2016, 02:08 PM

I think part of it is because the calculator only does the theory.
It does not account for wind, motor effeciency, LiPo quality, drag, friction in the driveline, etc.
But I could be wrong!
   
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09.06.2016, 02:28 PM

Are you using 3.7v/cell?

3.7 is far more accurate and realistic to what the car will see under load compared to 4.2v/cell.

Is this in your 5b? It's a big car, lots of wind resistance.

Are you looking at the data for your runs? Maybe your batteries aren't up to the task.


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jcflyer
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09.06.2016, 03:52 PM

Quote:
Originally Posted by _paralyzed_ View Post
Are you using 3.7v/cell?

3.7 is far more accurate and realistic to what the car will see under load compared to 4.2v/cell.

Is this in your 5b? It's a big car, lots of wind resistance.

Are you looking at the data for your runs? Maybe your batteries aren't up to the task.
Yes I am using 3.7 yes this is my SC truck with a cage, and yes I am looking at the ESC history. The batteries are up to it for sure, they do get pulled down by 4 volts on one of these runs!!! The batteries are still above 44.4 volts during these runs...
   
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RC-Monster Mike
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09.06.2016, 09:20 PM

I doubt you're holding 3.7 volts under load unless its geared pretty conservative - gotta guess on tire ballooning as well(soft tires will grow more). For speed run applications, I set the voltage to whatever the LVC is set to. For day-to-day, I use 3.2 for calculations....I rarely verify the actual speed, though(unless its a speed run, I don't care what the actual number is - more of a feel thing for regular running).
   
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jcflyer
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09.06.2016, 09:50 PM

Quote:
Originally Posted by RC-Monster Mike View Post
I doubt you're holding 3.7 volts under load unless its geared pretty conservative - gotta guess on tire ballooning as well(soft tires will grow more). For speed run applications, I set the voltage to whatever the LVC is set to. For day-to-day, I use 3.2 for calculations....I rarely verify the actual speed, though(unless its a speed run, I don't care what the actual number is - more of a feel thing for regular running).
It is geared pretty easy 17t/54t pinion and spur gears. The ESC has a log and it shows the voltage to be above 44.4 volts on a full charge, I have be down around the 70ish% range before it dips below 44.4 volts. The tires are BRP slicks the have absolutely zero ballooning in them!!! I am not doing speed runs this is drag racing 132'!!! I don't really care about the numbers that much I was just comparing the logs to the calculator, trying to figure which is accurate!!! That way I can tune it better...
   
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09.06.2016, 10:53 PM

Quote:
Originally Posted by jcflyer View Post
It is geared pretty easy 17t/54t pinion and spur gears. The ESC has a log and it shows the voltage to be above 44.4 volts on a full charge, I have be down around the 70ish% range before it dips below 44.4 volts. The tires are BRP slicks the have absolutely zero ballooning in them!!! I am not doing speed runs this is drag racing 132'!!! I don't really care about the numbers that much I was just comparing the logs to the calculator, trying to figure which is accurate!!! That way I can tune it better...
Between the short run and tire slipping are you sure you're reaching top speed? Most speed runs take a long long way to reach top speed.

If all you're going by is the speed through the timing lights, I bet that is your problem.


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jcflyer
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09.06.2016, 11:39 PM

Quote:
Originally Posted by _paralyzed_ View Post
Between the short run and tire slipping are you sure you're reaching top speed? Most speed runs take a long long way to reach top speed.

If all you're going by is the speed through the timing lights, I bet that is your problem.
Well no I have taken it out from a rolling start and took it flat out for longer and the numbers are the same..
   
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09.08.2016, 07:31 AM

Eh, it's a great tool, but it isn't perfect. If we could assure the batteries and components all did what they were rated to do, had zero friction in the world and tested in a vacuum the calculator would be spot on.

Got any vids of your drag racing? I'd love to see this action.


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