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Mike Keely
2010.02.15, 09:36 AM
My main question is about batteries. We have a 4 hour enduro coming up on March 13th in PA.

Would you use a battery that had longer run time over a battery that gave you faster laps?

There are 60 min. per hour X 4 = 240 minutes in the race. I have not checked yet but lets say it takes 1.5 mins. per battery change. If we are doing 6 second laps that equals about 15 lost laps in a battery change.

I get 30 minutes on a battery now, so that means seven battery changes in 4 hours.

If I can get 40 min. out of a battery I can drop off two battery changes.

Let me know if my math is correct.
6 second laps with 900 Mah batteries.
6.2 second laps with ???? Mah batteries.


30 min per battery X 60 sec. a min / 6.0 sec laps = 300 laps every 30 mins. This averages out to 10 laps a min. X 240 min. = 2400 laps minus 30 laps for the 2 extra battery changes = 2370 laps in 4 hours


40 min per battery X 60 sec. a min / 6.2 sec laps = 387 laps every 40 mins. This averages out to 9.67 laps a min. X 240 min. = 2322 laps in 4 hours


I know that I did not add in the other battery changes so the true totals are not 100 % the correct totals.



Here are my two questions.

Would using a higher Mah battery add .2 seconds a lap?

Would I be able to gain ten minutes to my run time using a higher Mah battery?

EMU
2010.02.15, 12:40 PM
One thing to point out. A higher mah batter will not necessarily yield longer runtime. They may have more mah, but at once they start to get through the discharge, they will drop in voltage more than the lower mah cells. So you will be running with a pack that feels like it has dumped midway through the run. With a faster motor, that isnt much of a problem, but with a 70t it may be a difference of .5-1s per lap depending on the layout.

I think 20-25 minute stints are more realistic... especially since it gives you time to cool the tires or put new rubber on, and more important, take a break from driving. The way you drive is very important as well. When the batteries are fresh, you want to drive the car nice and easy, less throttle input, and as the pack runs, pick up the pace.

How many tire changes are you planning?

chad508
2010.02.15, 01:08 PM
why in the world would it take 1.5 minutes to replace batts. should take more like 15 sec.

hrdrvr
2010.02.15, 02:15 PM
^ Chad, if you look at the average pit stops of the teams at our enduro, they were between 1:15 and 1:45. Of course, we werent allowed to change at track side, and this included going back to your pit and returning.

FWIW Mike, My team mate and I deliberated over this same thought before the race. We decided to have both types (Orion 1100s and 750s) of batteries ready, as well as having some mid range batts (900s) charged hot, and some charged mild. In the end the hotter battereis with the lower charge ratings (750s charged at 1a) were what worked best for us. We couldnt afford to be giving up the tenths the slower battereis were giving us. We decided that we would rather try and match our competition in the pits, and beat them on the track, as opposed to chasing on the track, and trying to make it up in the pits. We pretty much ran a faster pace than any one else here except reflex, and we finished in front of every one...except reflex :D

Take this with a grain of salt though. We were running a speedy 07 in the mod class against hotter motors, and needed the extra kick. I think if we were all running 70ts, Id be looking for whatever speed advantage I could find!

Mike Keely
2010.02.15, 09:41 PM
One thing to point out. A higher mah batter will not necessarily yield longer runtime. They may have more mah, but at once they start to get through the discharge, they will drop in voltage more than the lower mah cells. So you will be running with a pack that feels like it has dumped midway through the run. With a faster motor, that isnt much of a problem, but with a 70t it may be a difference of .5-1s per lap depending on the layout.

I think 20-25 minute stints are more realistic... especially since it gives you time to cool the tires or put new rubber on, and more important, take a break from driving. The way you drive is very important as well. When the batteries are fresh, you want to drive the car nice and easy, less throttle input, and as the pack runs, pick up the pace.

How many tire changes are you planning?None. I trued down some LM rears so they are a little over the stock size rears and going with a good size front tire.

EMU
2010.02.15, 10:50 PM
A set of ATM 40 fronts should easily last the entire race, and then some... LM rears is a good rear. More grip than 20 slicks, and lasts a lot longer due to the larger diameter. Make sure to round the sidewalls a little though and I would glue them to the wheels, dont take any risks.