The best lipo for my setup?
02-18-2010, 10:15 PM
#1
The best lipo for my setup?
I just purchased a used rc8e with mamba monster 2650kv. It is geared at 50t spur and 16t pinion. I run on a medium sized dirt track and I want around 20-30 minute run times.
I'm new to lipo so I would like to stick with ONE battery to start out.
Any suggestions on 3s, 4s, mah etc.?
I'm new to lipo so I would like to stick with ONE battery to start out.
Any suggestions on 3s, 4s, mah etc.?
02-18-2010, 11:59 PM
#2
Tech Addict
I know the nitro RC8 has a 4.5 ratio in the front and rear gearboxes, so assuming the RC8e is the same, I think it is geared pretty good for 4S, and a bit slow for 3S. I would target about 37 mph for a medium track. I was a little higher and will be going to a little lower, but anywhere from 35 to 40 mph is a good start and then watch temps and relative speed to others to dial it in from there.
On 4S that motor shoud hit about 39,220 rpm. 16 to 50 give you a center shaft speed of 12,550,4 rpm. 4.5 diffs drop that to a wheel sspeed of 2789 rpm. 1/8 buggy tires run about 4.3 inches tall. About 13.5 inches per revolution. Plugging in the numbers I get just under 36 mph. Try it, and you should be plenty fast.
Getting 20 to 30 minutes of run time is a different story. The course layout, your driving style, the car setup, and even the track surface will all effect how long you can run. I run a smaller motor than most, so it is less power, but it is also less efficient, so my power drain might not be a perfect estimate, but on what I consider a medium sized technical track with one good fast straight, I am pulling an average of 240 to 270 watts. My fastest lap today pulled 265 average and peeked to 1385 watts. On 4S, use 15 volts to make the math easy. 265 / 15 = 17.7 amps average. If you want that for a half hour, you need a pack of 8,850 mah. OUCH that is a big pack. Several of my laps were a bit lower, but I always like to err on the bad side to be covered. I use my peek wattage to determine the C rate needed. 1385 watts / 15 volts = 92.33 amps.As high as this laps average power was, this current peak is on the low side. I hit as high as 1697 watts or over 112 amps. I run 5000 35C packs, they are obviously fine as the rated current is 175 amps 5.000 AH (5000mah) x 35C = 175 amps. But my projected run time is only 16.9 minutes. I may be able to stretch it to 20 minutes, but that seems about the normal limit on this size pack. For a real 30 min run, I think you will need a lower KV motor and a 6S 5000mah or larger pack. Higher voltage will make more power at less current. Check wih your local track though. Some only allow to 4S and they may limit the length of electric runs Here they only run 10 minute mains
On 4S that motor shoud hit about 39,220 rpm. 16 to 50 give you a center shaft speed of 12,550,4 rpm. 4.5 diffs drop that to a wheel sspeed of 2789 rpm. 1/8 buggy tires run about 4.3 inches tall. About 13.5 inches per revolution. Plugging in the numbers I get just under 36 mph. Try it, and you should be plenty fast.
Getting 20 to 30 minutes of run time is a different story. The course layout, your driving style, the car setup, and even the track surface will all effect how long you can run. I run a smaller motor than most, so it is less power, but it is also less efficient, so my power drain might not be a perfect estimate, but on what I consider a medium sized technical track with one good fast straight, I am pulling an average of 240 to 270 watts. My fastest lap today pulled 265 average and peeked to 1385 watts. On 4S, use 15 volts to make the math easy. 265 / 15 = 17.7 amps average. If you want that for a half hour, you need a pack of 8,850 mah. OUCH that is a big pack. Several of my laps were a bit lower, but I always like to err on the bad side to be covered. I use my peek wattage to determine the C rate needed. 1385 watts / 15 volts = 92.33 amps.As high as this laps average power was, this current peak is on the low side. I hit as high as 1697 watts or over 112 amps. I run 5000 35C packs, they are obviously fine as the rated current is 175 amps 5.000 AH (5000mah) x 35C = 175 amps. But my projected run time is only 16.9 minutes. I may be able to stretch it to 20 minutes, but that seems about the normal limit on this size pack. For a real 30 min run, I think you will need a lower KV motor and a 6S 5000mah or larger pack. Higher voltage will make more power at less current. Check wih your local track though. Some only allow to 4S and they may limit the length of electric runs Here they only run 10 minute mains
02-24-2010, 04:36 PM
#3
I know the nitro RC8 has a 4.5 ratio in the front and rear gearboxes, so assuming the RC8e is the same, I think it is geared pretty good for 4S, and a bit slow for 3S. I would target about 37 mph for a medium track. I was a little higher and will be going to a little lower, but anywhere from 35 to 40 mph is a good start and then watch temps and relative speed to others to dial it in from there.
On 4S that motor shoud hit about 39,220 rpm. 16 to 50 give you a center shaft speed of 12,550,4 rpm. 4.5 diffs drop that to a wheel sspeed of 2789 rpm. 1/8 buggy tires run about 4.3 inches tall. About 13.5 inches per revolution. Plugging in the numbers I get just under 36 mph. Try it, and you should be plenty fast.
Getting 20 to 30 minutes of run time is a different story. The course layout, your driving style, the car setup, and even the track surface will all effect how long you can run. I run a smaller motor than most, so it is less power, but it is also less efficient, so my power drain might not be a perfect estimate, but on what I consider a medium sized technical track with one good fast straight, I am pulling an average of 240 to 270 watts. My fastest lap today pulled 265 average and peeked to 1385 watts. On 4S, use 15 volts to make the math easy. 265 / 15 = 17.7 amps average. If you want that for a half hour, you need a pack of 8,850 mah. OUCH that is a big pack. Several of my laps were a bit lower, but I always like to err on the bad side to be covered. I use my peek wattage to determine the C rate needed. 1385 watts / 15 volts = 92.33 amps.As high as this laps average power was, this current peak is on the low side. I hit as high as 1697 watts or over 112 amps. I run 5000 35C packs, they are obviously fine as the rated current is 175 amps 5.000 AH (5000mah) x 35C = 175 amps. But my projected run time is only 16.9 minutes. I may be able to stretch it to 20 minutes, but that seems about the normal limit on this size pack. For a real 30 min run, I think you will need a lower KV motor and a 6S 5000mah or larger pack. Higher voltage will make more power at less current. Check wih your local track though. Some only allow to 4S and they may limit the length of electric runs Here they only run 10 minute mains
On 4S that motor shoud hit about 39,220 rpm. 16 to 50 give you a center shaft speed of 12,550,4 rpm. 4.5 diffs drop that to a wheel sspeed of 2789 rpm. 1/8 buggy tires run about 4.3 inches tall. About 13.5 inches per revolution. Plugging in the numbers I get just under 36 mph. Try it, and you should be plenty fast.
Getting 20 to 30 minutes of run time is a different story. The course layout, your driving style, the car setup, and even the track surface will all effect how long you can run. I run a smaller motor than most, so it is less power, but it is also less efficient, so my power drain might not be a perfect estimate, but on what I consider a medium sized technical track with one good fast straight, I am pulling an average of 240 to 270 watts. My fastest lap today pulled 265 average and peeked to 1385 watts. On 4S, use 15 volts to make the math easy. 265 / 15 = 17.7 amps average. If you want that for a half hour, you need a pack of 8,850 mah. OUCH that is a big pack. Several of my laps were a bit lower, but I always like to err on the bad side to be covered. I use my peek wattage to determine the C rate needed. 1385 watts / 15 volts = 92.33 amps.As high as this laps average power was, this current peak is on the low side. I hit as high as 1697 watts or over 112 amps. I run 5000 35C packs, they are obviously fine as the rated current is 175 amps 5.000 AH (5000mah) x 35C = 175 amps. But my projected run time is only 16.9 minutes. I may be able to stretch it to 20 minutes, but that seems about the normal limit on this size pack. For a real 30 min run, I think you will need a lower KV motor and a 6S 5000mah or larger pack. Higher voltage will make more power at less current. Check wih your local track though. Some only allow to 4S and they may limit the length of electric runs Here they only run 10 minute mains
I also learned the maH is the 1000 amps per hour?
Now how did you detemine your average and peak wattage output? It sounds like you have some kind of device you are getting readings from.
Next on the "C" rating, you are taking the stated C rating multiplied by the stated mah divided by 1000 to determine the rated amperage for a particular pack.
Last how did you determine the projected run time to be only 16.9 minutes?
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