How exactly are people getting long run-times?

[nitrostarter]

I was thinking swapping to 5s and taming your driving skills. Your unloaded RPM's are 37740. This is a touch out of that efficiency range of 28-35k rpms. Dropping to 5s will put you are 31450 rpms which should be optimal.

[lutach]

When calculating speed with Brian's awesome calculator, try adding 1" (At least) of tire ballooning. My 2 truggies are geared for 34-36mph and they both are going over 40mph.

[Marvin]

Thanks, I normally add about 0.2" for tyre balooning considering they are only buggy tyres.

I'm going to drop to 4-5S, depending on how successful my quick-change battery conversion is.

Glad to see you got the files Mike.

I'm running 3S packs on my 808 with a MMM 2200Kv combo. I can get more than 20 minutes from a 8000mah pack, which weights 560g. I've got some 3S 5000mah packs that are 100g lighter, but i haven't tested them yet, i think i would get around 15 minutes.

I couldn't be happier with it, 0 problems. I know people running 4S and over who are always complaining about temps or runtime...most of them said 3S wasn't a good idea.

why would a 1400kv motor on 6s use less amps than an equivalent 1700kv motor, also on 6s and both geared for 35mph?

[BL_RV0]

Originally Posted by Marvin

Thanks, I normally add about 0.2" for tyre balooning considering they are only buggy tyres.

I'm going to drop to 4-5S, depending on how successful my quick-change battery conversion is.

Glad to see you got the files Mike.

You should add about .5" tire ballooning.

[lutach]

Originally Posted by drkdgglr

why would a 1400kv motor on 6s use less amps than an equivalent 1700kv motor, also on 6s and both geared for 35mph?

In general a lower Kv motor would have lower turns and offer higher torque. There are other factors that plays in this as well, but I'm not an engineer and would hate to give out the wrong info.

Originally Posted by lutach

In general a lower Kv motor would have lower turns and offer higher torque. There are other factors that plays in this as well, but I'm not an engineer and would hate to give out the wrong info.

Wouldn't you only benefit from this extra torque in a low kv & high voltage setup vs a high kv and low voltage setup?

Although the 1400kv motor would have more torque than a 1700kv, you'd have to gear the 1400kv motor higher to reach the same speed as the 1700kv motor.

I entered two buggy setups in the speedalc. Only difference between the two is gearing and motor. I used a 1515 3d (1360kv) and 1515 2.d (1650kv). According to the calc the 1360 kv has more motor torque, but the final torque is exactly the same as the 1650kv setup. I am assumng that both setups would have the same amp draw (this is were I could be going wrong)

1515 3d:
Total Motor Speed: 28886.4 RPM
Vehicle Speed: 34.83 mph (55.94 km/h)
Effective KV Value: 1301.19
KT constant: 0.99 oz-in/A
Motor Torque: 0.41 ft-lbs
Final Torque: 4.6 ft-lbs
Final Power: 1776 watts (2.4 HP)

1515 2.5d
Total Motor Speed: 35310 RPM
Vehicle Speed: 34.93 mph (56.12 km/h)
Effective KV Value: 1590.54
KT constant: 0.82 oz-in/A
Motor Torque: 0.34 ft-lbs
Final Torque: 4.62 ft-lbs
Final Power: 1776 watts (2.4 HP)

Another thing I was thinking is that you'll be running the 1360kv motor closer to it's max rated amps and will run hot easier?

[lutach]

Originally Posted by drkdgglr

Wouldn't you only benefit from this extra torque in a low kv & high voltage setup vs a high kv and low voltage setup?

Although the 1400kv motor would have more torque than a 1700kv, you'd have to gear the 1400kv motor higher to reach the same speed as the 1700kv motor.

I entered two buggy setups in the speedalc. Only difference between the two is gearing and motor. I used a 1515 3d (1360kv) and 1515 2.d (1650kv). According to the calc the 1360 kv has more motor torque, but the final torque is exactly the same as the 1650kv setup. I am assumng that both setups would have the same amp draw (this is were I could be going wrong)

1515 3d:
Total Motor Speed: 28886.4 RPM
Vehicle Speed: 34.83 mph (55.94 km/h)
Effective KV Value: 1301.19
KT constant: 0.99 oz-in/A
Motor Torque: 0.41 ft-lbs
Final Torque: 4.6 ft-lbs
Final Power: 1776 watts (2.4 HP)

1515 2.5d
Total Motor Speed: 35310 RPM
Vehicle Speed: 34.93 mph (56.12 km/h)
Effective KV Value: 1590.54
KT constant: 0.82 oz-in/A
Motor Torque: 0.34 ft-lbs
Final Torque: 4.62 ft-lbs
Final Power: 1776 watts (2.4 HP)

Another thing I was thinking is that you'll be running the 1360kv motor closer to it's max rated amps and will run hot easier?

From what I've seen in my set ups, all the higher Kv motors geared for the same speed have always asked for more AMPs then with a lower Kv ones. It might have to do with the winding resistance (Rt) and the fact that most higher Kv motor have higher Io (No Load Current). For example: A Aveox 1415/2Y has a Rt of 0.022 Ohms and a Io of 1.8, now a 1415/1.5Y has a Rt of 0.010 Ohms and a Io of 2.5. I have tried the 2 motors above with 6S both geared for the same speed and the 1.5Y was always warmer and pulled more AMPs then the 2Y.

thanks lutach. so a higher torque motor will draw less amps?
then how does the speedcalc calculate torque? if the motor draws more amps in the calc, the torque is higher... I'll post this q in the speedcalc thread.

[lutach]

Originally Posted by drkdgglr

thanks lutach. so a higher torque motor will draw less amps?
then how does the speedcalc calculate torque? if the motor draws more amps in the calc, the torque is higher... I'll post this q in the speedcalc thread.

Not sure how the calculator works that out. I'm sure when Brian sees this he'll have more info on it.

[SpEEdyBL]

If you gear a 1400 kv motor and a 1700 kv motor for the same speed, the 1700 kv motor will accelerate faster because it will draw more current and therefore more power. It may also heat up a little more, but the lower resistance keeps that from happening so much.

From my experience, my Neu-Castle 2650 on 4s geared 14/46 is about the same top speed as my Tekin T8 1900 kv motor geared 20/46. The 2650 accelerates fairly hard, and the 1900 is pretty sluggish, but the 1900 runs a good 15-20 degrees cooler. The 1900 on 6s geared 14/46 blows the 2650 on 4s out of the water in speed, acceleration and temps.