How exactly are people getting long run-times?
 

I'd like to know how people are getting over 20 minutes on a single battery without stupidly high capacitys, weight or voltage.

How?!?

I simply cannot get the run-time out of the same batteries as some of you guys.

My current set-up uses a 6S 6100mAh battery to get just over 20 minutes on the track, but as a result the car weighs 4.1kg! That's truggy weight, but it's a buggy!

My original set-up was 4S 4350mAh which would earn me 11 minutes at a push. I can't do battery changes as I'm just not quick enough to make up the time lost to the nitros. Is it a case of gear down to less than the nitro buggies to get a bit of economy?

Have I gone the wrong way? Do I need smaller batteries, and a far lighter car?

Please help! I'm at my wit's end.

Wow, 6s 6100 in a buggy, and ~20 min? I have a 5s 5200 in a truggy and I'm easily getting 20 and I know I get 30 min bashing. How freely does the buggy roll with and without the motor pinion engaged?
I saw someone at a track with his pinion way tight against his spur and he was complaining about punch and speed. It could have been his batteries, but the tight mesh certainly wasn't helping.

It's definately free, there's no binding, and when my rotor failed on Sunday, I took the complete centre diff out (with motor still attached) and I was able to spin the spur/pinion combination like a clutch bell with those really nice 'almost failed' bearings that spin really freely.

I just thought that the tracks we race on in the UK aren't anywhere near as smooth as in the US, and also we have fewer jumps, which don't take that much throttle in comparison to sweeping corners, so presumeably the run time will be less anyway.

5s 4500mah in my truggy get me over 15 minutes on the track. What buggy, motor, battery, and gearing are you running? You may be overgeared. I'm only geared for ~36, 50/15, just a touch faster than the nitros on the straight but enough torque to kill them at every corner

Also.... Throttle control has a big part in runtime! Drive it like a nitro and your run time will suffer. Drive it like a 1/10 stadium truck and you'll gain a couple minutes, you gotta roll on the throttle smoothly, don't keep giving it bursts like a nitro

Set-up:
D8 - Stock, so not exactly light.
Tekin RX8 w/T8 1700kV - minimum timing
Gearing 15/48 - so according to BrianG's calculator, it should be good for ~39mph
PolyRC 6S 6100mAh battery.

I'm thinking to invest in all the lightweight upgrades, see what it does to my run-time, then drop the battery size a bit. Also I'll probably gear lower (to ~35mph).

we gear for about 34mph im geared for 32mph right now. i can get 20 min on a 5ah 4s 30c pack. the c rating is also a factor.

These are the factors as I see it. Some of these may not apply to you and have already been mentioned:

- Gearing. As said, gearing lower will help a lot. The higher you gear, the more work is being done, so more current will be drawn reducing runtime.

- Cell quality. If you are approaching the cell max capability, you actually get less mAh out of it. Check an eagletree graph sometime. You'll see a 5Ah pack actually getting ~4500mAh of usable capacity if drawn hard. It gets worse the harder you run it. If your pack is rated for 40C and you only pull 20C, you will get more usable capacity.

- Drivestyle. Those heavy starts and heavy acceleration are impressive to watch, but also generates heavy current spikes, which kills runtime. Try to maintain a more constant speed so you accelerate from a faster speed, which reduces those burst currents. This takes good driving.

- ESC settings. Increasing punch control can further help tame those burst currents. This setting basically stretches out the time the ESC accelerates the motor no matter how fast you pull the trigger. The downside to this is you have less "snap" and in-air correction can be a little more sluggish. Hardcore racers generally don't like this. Also, setting your timing to the optimum setting can boost efficiency. So instead of losing power as motor/ESC heat, more of it gets to the ground. The optimum setting depends on the motor though, so you may have to research.

- Terrain. Anything other than smooth and flat takes more power to push through (like grass or beach sand). On the other hand, loose gravel can actually help since grip is less and burst current is lower.

- Weight. Obviously, more weight takes more power to haul around. This is why sometimes simply going to a larger capacity battery is not the answer as those cells are heavier for a given voltage. And lighter tires (unsprung weight) can help a lot as well.

- Voltage being used. Higher voltage on a lower kv motor is more efficient. Higher currents creates voltage drop on any resistances (wires, connectors, FETs, etc). Lower current reduces these drops so efficiency goes up.

Mine is a D8 at 8 lbs, Tekin 1700 buggy, 4S 4000 35C, 17/40 gear, 0 timing and 70 throttle limiting, very free running drivetrain and very gentle on the throttle inputs. I've done 18 minutes with this combo and didn't hit up against the LVC set at 3.3v/cell.

So, my action plan then:

1. Gear down a tad.
2. Tame my driving, possibly also using punch control.
3. Lighten the D8.
4. Use lighter cells, of higher quality.
5. Try to use the smoother parts of the track,not so much of an issue recently.
6. Stick with 6S. One question though, 6S on 1700kV? Is it a good idea considering the low current requirement?


Thanks guys, that's been really useful! Just need to put it into practice now.

also clean and lube your bearings every 2 weekends. it helps with the drag

I run both an 8ight-t 8ight-b and a e-revo and the truggy and e-revo both get about 12 minutes of run time on 4s 35c 5k packs, the buggy gets about 13. All are geared for at or just under 40mph. I have a 5s 6k pack I run in my truggy for longer a-mains as well, this gets me enough to do a 20min, but not quite enough for 30min typically. One battery swap in a 30min main works out though if it's a smooth swap.. keeping pit time evened out.

Marvin,
Try swapping to the 1400Kv motor on 6s Lipo for starters. The 1400Kv motor is the best option for this voltage IMO, and will be generous in regards to runtime. I would surmise that your driving style is also a factor - I can get the same runtime you get on a 4s 6000mah pack - only 3/4 the battery power(and while I am no pro, I don't suck, either). I use a 1900Kv system on 4s geared for around 40mph in my buggy. The 1700Kv on 6s will suck more power, but the 1400Kv on 6s should be pretty close to my setup.
Someone above mentioned to drive it like a 1/10 truck(meaning smooth throttle input) - this will make a big difference vs the constant "pulsing" that is often carried over from nitro drivers. In nitro, pulsing the throttle is helpful to keep the clutch engaged to a certain degree - in electric, it wastes power and upsets the chassis. Dropping this habit will lower mah usage and temps significantly.
So...swap to 5s Lipo or the 1400kv motor and focus on smooth throttle input and you should see a noticeable improvement in runtime(assuming there is no binding, etc. as also mentioned above).

I think I may swap to 5S then. Or, if my quick change system works (you've probably received a multitude of emails from me (Simon Turner) about this recently, use the latest one, its got decent files, I had a right problem with getting a normal file type, but I've got it sorted and sent IGES files), I'll be running 4S.

Yes - I got lots of emails with files I couldn't see, but did see the IGES files this morning(though i haven't looked at them yet). :)

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.

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.

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?

You should add about .5" tire ballooning.

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?

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.

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

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.