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Old 01-09-2011, 05:44 PM   #1
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Default Calculating Runtime

What is the best way to determine runtime? We usually have 5min qualifiers and 10min mains. I realize there is no easy answer but I'm wandering what everyone else does.
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Old 01-09-2011, 05:53 PM   #2
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What is the best way to determine runtime? We usually have 5min qualifiers and 10min mains. I realize there is no easy answer but I'm wandering what everyone else does.
What mah battery are you running? Lipo or Nimh? I personally don't calculate, but there are some tricks you can do to increase run time. If you ran a 2S 5000mah Lipo, that would be plenty for any qualifier or main assuming it's in a Brushless SC10 like your signature.
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Old 01-09-2011, 05:59 PM   #3
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What mah battery are you running? Lipo or Nimh? I personally don't calculate, but there are some tricks you can do to increase run time. If you ran a 2S 5000mah Lipo, that would be plenty for any qualifier or main assuming it's in a Brushless SC10 like your signature.
Venom 2s 4000 lipo with a 17.5 Murf Dogg motor. However, I watched someone running a Venom 2s 5000 lipo with a Novak Ballistic motor dump at the 8min mark of a 10min main. They were able to finish but had difficulty making even the easy jumps. This got me thinking how I should determine my runtime and how to adjust for mains.
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Old 01-09-2011, 06:16 PM   #4
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I have the same motor and battery, Id say I get at least 20 min (if not 30) race/practice time on a 36x80 track. Id say he didnt top off.
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Old 01-09-2011, 06:26 PM   #5
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What is the best way to determine runtime? We usually have 5min qualifiers and 10min mains. I realize there is no easy answer but I'm wandering what everyone else does.
not that difficult

over a period of about 10 or so 5 min heats, note how many mah you put back into the pack each charge.
Work out the average MAH you put back in then you'll know your consumption rate over 5 min. Divide by 5 then you have MAH/min then you'll know roughly runtime for the pack you use.

(MAHheat1+MAHheat2+.......+MAHheat10)/10 = MAH5min

MAH5min/5 = MAH/min

you get the drift...

you only have to do this once for each car/setup... And assuming your packs are of reasonable qualitly, ie the rated capacity is correct, you can work out how many mins you get fo each pack.
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Old 01-09-2011, 06:33 PM   #6
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I have the same motor and battery, Id say I get at least 20 min (if not 30) race/practice time on a 36x80 track. Id say he didnt top off.
He was running a Mamba Max Pro with 81/22 gearing on his SC10. We are turning around 23 second laps. I know the Novak has 30deg of timing on motor. I believe the timing boost is set at 35deg at 2700 to 9700 rpm. What does everyone else do?
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Old 01-09-2011, 06:36 PM   #7
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not that difficult

over a period of about 10 or so 5 min heats, note how many mah you put back into the pack each charge.
Work out the average MAH you put back in then you'll know your consumption rate over 5 min. Divide by 5 then you have MAH/min then you'll know roughly runtime for the pack you use.

(MAHheat1+MAHheat2+.......+MAHheat10)/10 = MAH5min

MAH5min/5 = MAH/min

you get the drift...

you only have to do this once for each car/setup... And assuming your packs are of reasonable qualitly, ie the rated capacity is correct, you can work out how many mins you get fo each pack.
Ok, that sounds good. How do you adjust if you determine the battery pack's runtime isn't enough? Is there like a rule of thumb? ie. go up or go down teeth on pinion or spur?
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Old 01-09-2011, 06:37 PM   #8
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Ok, that sounds good. How do you adjust if you determine the battery pack's runtime isn't enough? Is there like a rule of thumb? ie. go up or go down teeth on pinion or spur?
if your car is running with reasonable temps... then the only thing you can do is adjsut your driving. ;-)
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Old 01-09-2011, 06:42 PM   #9
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Were you also wondering if there was a way to know what size (mah) lipo to get according to needed runtime and knowing the motor specs?
Like an equation?
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Old 01-09-2011, 06:49 PM   #10
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Were you also wondering if there was a way to know what size (mah) lipo to get according to needed runtime and knowing the motor specs?
Like an equation?
I would be interested in anything that could help determine runtime. How does the final drive ratio effect the runtime and motor temps?
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Old 01-09-2011, 07:44 PM   #11
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Old 01-09-2011, 07:53 PM   #12
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I would be interested in anything that could help determine runtime. How does the final drive ratio effect the runtime and motor temps?
I use 2 equations to get me pretty close to my needs before even buying a lipo using the max amp rating of the motor.

It is just to get a good estimate but not to hold your numbers as absolute.
But anyone who tries this will see it can be used as a very good tool to estimate what lipo size (mah) for a specific runtime.

Amp/hr x 200 / current = minimum runtime
Amp/hr x 250 / current = maximum runtime

*(Amp/hr = mah / 1000)

Use the minimum and maximum to put you in a way better position in knowing the size lipo you need.
(*this system works best with 2s for 1/10 scale and 4s for 1/8 scale)

The last thing to understand about my system is that the runtime number that you will get is only to take your lipos down to nominal voltage (3.7v per cell), not any further, so with this being said there is actually more runtime for those who set their lvc lower than 3.7v per cell.

Now when using HV setups with low kv motors simply start with a motor that will give around 30,000-35,000rpm's for your 2s or 4s application (*see note above).

Now that you know the Amp/hr for that runtime use the known Amp/hr number in the following equation:

Amp/hr x nominal voltage of pack / nominal voltage of the HV pack

ex:
9 = (Amp/hr)
9 x (4s=14.8v)
9 x 14.8 / (5s=18.5v)
9 x 14.8 / 18.5 = Amp/hr
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Last edited by KingdomRacer; 01-09-2011 at 08:26 PM. Reason: further explanation
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Old 01-09-2011, 09:20 PM   #13
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I have the same motor and battery, Id say I get at least 20 min (if not 30) race/practice time on a 36x80 track. Id say he didnt top off.
Dirtracer68 is talking about me and the pack was complete charged.
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Old 01-09-2011, 11:42 PM   #14
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Dirtracer68 is talking about me and the pack was complete charged.
Wow! Your pack dumped at 8min? Bummer, what pack are you running?
I just recently ran an 8 minute main with roughly 2 minutes of warmup and didnt even burn 2000mah out of a 5600mah pack! In theory I could run it in theory I could run it 15 minutes and be fine!
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Old 01-10-2011, 08:50 AM   #15
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Wow! Your pack dumped at 8min? Bummer, what pack are you running?
I just recently ran an 8 minute main with roughly 2 minutes of warmup and didnt even burn 2000mah out of a 5600mah pack! In theory I could run it in theory I could run it 15 minutes and be fine!
Im running a venom 5000mah 40c battery. I just charged the pack again and it only used 1698 mah which would only be 169.8 a minute. The motor at 10 mins was only 106 degrees.
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