Can someone explain 'Volt down, gear up' to me?

[SirCrashALot]

This may be a dumb question, but i really don't get it.
Ok I get that gearing up may be necessary to regain the speed lost from lower voltage.
But exactly this feels counter intuitive to me:
Lower voltage results in higher amp draw. (P=VxA)
Gearing up also results in higher amp draw. (higher load).
That's already two things that may heat up the system.
Another reason why i am asking is:
I already run my Mojave on 3S, 4S and 6S, no problems, without ever changing the pinion.

So apart from the general opinion and consensus on this, does anyone have a scientific/technical explanation?

 

[Cypher]

It depends on the motor kV also.
If you drive Mojave on 3S, it's not that fast, so if you want same speed you must gear up.

 

[SirCrashALot]

That makes sense.
But it is said all over the various forums, including AF, that a bigger pinion is required when going to a lower voltage, all else remaining the same.

 

[Cypher]

I guess that's for the speed. If you keep same pinion on 3s as you have on 6s, it will be slow. But if you don't mind, run 3-4S on Mojave with small pinion, and you will never have heat issues. Run 6s on 2200kv motor with 26t pinion will be a moster on speed and prob run really, really hot.

 

[GraniteFox]

Here is a speed calculator to give you the concept. https://www.radiocontrolinfo.com/information/rc-calculators/rc-car-calculator/

 

[Sandracer_NL]

I see it as riding a bicycle (he I’m from the Netherlands ).
If your gear (pinion) is too high your leg muscles (motor power=Watts) need to provide everything they can (deliver amps) to get to speed, which may not be enough. You will be exhausted real soon.
On the other side, gear too low within a few seconds you‘ll be paddling at full speed (continuously running at full power=Watt) without going fast, also exhausting you quickly. As a result gearing too low can actually make your motor run hotter.
The key is to find that (gearing) range in between.
With less volts that gearing range becomes lower. And as you already mentioned, with the same amount of power, less volts means higher amps which your esc and lipo(s) should be able to provide.

 

[Cypher]

I see it as riding a bicycle (he I’m from the Netherlands ).
If your gear (pinion) is too high your leg muscles (motor power=Watts) need to provide everything they can (deliver amps) to get to speed, which may not be enough. You will be exhausted real soon.
On the other side, gear too low within a few seconds you‘ll be paddling at full speed (continuously running at full power=Watt) without going fast, also exhausting you quickly. As a result gearing too low can actually make your motor run hotter.
The key is to find that (gearing) range in between.
With less volts that gearing range becomes lower. And as you already mentioned, with the same amount of power, less volts means higher amps which your esc and lipo(s) should be able to provide.

So, the best would be to gear up to the point where you rarely use full power, to keep motor at a lower rpm and still have comfortable speed at 3/4 power? And full throttle only for straight asphalt speed runs?

 

[Sandracer_NL]

So, the best would be to gear up to the point where you rarely use full power, to keep motor at a lower rpm and still have comfortable speed at 3/4 power? And full throttle only for straight asphalt speed runs?

You can run full power more than rarely, but I once had my motor run hot and geared down (I was running the 12T 6s pinion on 4s) to a 11T. This made my motor run even hotter, because I was running on full throttle even more, because it was at a pretty low top speed within seconds. Then I geared up to a 15T and motor temps actually dropped. I tried a 19T and the motor started cogging pretty bad and I was seeing esc and lipo temps going up. I even got a esc shutdown.
Now I now that for that RC car (desert buggy) ‘the‘ range on 4s is in the 15T-17T range (also depending on ambient temperatures of course, tires size/weight, lipo quality, and terrain you run on).

 

[SirCrashALot]

I see it as riding a bicycle (he I’m from the Netherlands ).
If your gear (pinion) is too high your leg muscles (motor power=Watts) need to provide everything they can (deliver amps) to get to speed, which may not be enough. You will be exhausted real soon.
On the other side, gear too low within a few seconds you‘ll be paddling at full speed (continuously running at full power=Watt) without going fast, also exhausting you quickly. As a result gearing too low can actually make your motor run hotter.
The key is to find that (gearing) range in between.
With less volts that gearing range becomes lower. And as you already mentioned, with the same amount of power, less volts means higher amps which your esc and lipo(s) should be able to provide.

Well, shouldn't i see any difference running the same system on different voltages, then?
Because i really don't.
Or is it just that, because of the lower voltage, the motor doesn't run as high revs?
Or is it that i haven't tried going for maximum speed in the first place and just use a moderate gearing?

 

[Sandracer_NL]

Well, shouldn't i see any difference running the same system on different voltages, then?
Because i really don't.
Or is it just that, because of the lower voltage, the motor doesn't run as high revs?
Or is it that i haven't tried going for maximum speed in the first place and just use a moderate gearing?

I think you’re at a moderate gearing, where the esc and lipo can provide the amps the motor is asking for.

 

[Cypher]

I run 1600kv motor on 6S with 18T pinion on my Mojave, and is happy with that. Could maybe bump it up to 20T, but I feel it's really fast enough on full throttle now. Around 65-70km/h.
Also, upon LVC, I can hold on the motor and not burn my fingers.

 

[SirCrashALot]

I run 1600kv motor on 6S with 18T pinion on my Mojave, and is happy with that. Could maybe bump it up to 20T, but I feel it's really fast enough on full throttle now. Around 65-70km/h.

What motor size are you using?
Because i have a HW4985 on 22t and a CC1520 on 20t. The CC on 18t got hot in a hurry, due to over revving. Just like Sandracer mentioned.

So, the best would be to gear up to the point where you rarely use full power, to keep motor at a lower rpm and still have comfortable speed at 3/4 power? And full throttle only for straight asphalt speed runs?

I guess so

 

[Cypher]

What motor size are you using?
Because i have a HW4985 on 22t and a CC1520 on 20t. The CC on 18t got hot in a hurry, due to over revving. Just like Sandracer mentioned.

I guess so

I have the HW4985 and max6.m combo.

 

[dure16]

Instead of butchering the topic with my own words, I’ll quote John Holmes (Holmes Hobbies) who is the guy famous for the quote:

“Volt up, Gear down! This has been our motto for a decade, and it still holds true for motors of all types. Using voltage to gain motor speed while gearing down to slower wheelspeeds is win-win. Torque at the wheel is gained, low speed control is improved, and overall horsepower will increase as compared to low voltage and high geared systems.”

 

[SirCrashALot]

Instead of butchering the topic with my own words, I’ll quote John Holmes (Holmes Hobbies) who is the guy famous for the quote:

“Volt up, Gear down! This has been our motto for a decade, and it still holds true for motors of all types. Using voltage to gain motor speed while gearing down to slower wheelspeeds is win-win. Torque at the wheel is gained, low speed control is improved, and overall horsepower will increase as compared to low voltage and high geared systems.”

True.
But I mounted a bigger motor for better reliability without heat concerns. The original motor runs hot. Bigger motors on 6S are ridiculously overpowered.
I think I got it just right, for me, with the bigger 6S motors on 4S.
I was just confused why everyone always suggests to gear up.

 

[Sandracer_NL]

I run 1600kv motor on 6S with 18T pinion on my Mojave, and is happy with that. Could maybe bump it up to 20T, but I feel it's really fast enough on full throttle now. Around 65-70km/h.
Also, upon LVC, I can hold on the motor and not burn my fingers.

Yup, I also like to run the Mojave in the 19T-21T range on the Max6 combo. I run it on both 4s and on 6s.

 

[Snowmandk]

True.
But I mounted a bigger motor for better reliability without heat concerns. The original motor runs hot. Bigger motors on 6S are ridiculously overpowered.
I think I got it just right, for me, with the bigger 6S motors on 4S.
I was just confused why everyone always suggests to gear up.

Where is that confusion coming from? You got most of the basics right.

Lower voltage means the motor turns slower so you need to gear up if you want the same speed.
That’s it.

If you run a 4s instead of 6s without changing anything else (motor kV, pinion/spur) you will be going about 33% slower and have 33% less power.
You won’t pull more amps though, because you are outputting a lot less power than on 6s!

Now, if you gear up to the same speed as on 6s then yes, power output needed is the same, but the voltage is lower so amps are going to go through the roof and everything runs hotter.

If you don’t notice a difference between a 3s and 6s on the stock electronics/gearing on your Mojave, then something must be wrong with your car…or you. No offense

 

[SirCrashALot]

Of course i noticed the speed difference. That what it was all about, anyway.
I noticed no difference in temps.
Good explanation btw.
Thanks.

 

[Snowmandk]

Oh right, no difference in temps makes more sense, I am a bit slow sometimes .

That’s most likely due to the way you drive and many other variables that have an effect on temperatures.

If you were to just go full throttle for 10 minutes straight on each battery/voltage (all else being equal) you’d definitely see a difference in temps at the end.