Scale Calculations equal to 1:1

[SpeedAssault]

Just about finished my 1/5 Brushless CC2200 6s 30c lipo
total reduction 11.5
motor spd 47256 RPM
calculated speed 60.72 MPH


Axle torque 4.45
motor power 3.5 HP

Brians Calculator is awesome http://www.scriptasylum.com/rc_speed/_units.html

What is the calculation for these: what does
3.5 HP in 1/5 scale convert to in 1:1 scale
and 4.45 ft-lbs

thanks

[Metallover]

3.5(5)=17.5 hp.

Keep in mind electric motors are rated for continuous horsepower not peak like ICE engines. Check out some EV conversions and how much power they have.

[SpeedAssault]

I should have known that.
numbers are not as exciting as hoped


thanks

[Metallover]

Well, weigh the car then see how that matches up to scale. The power/weight ratio should be pretty amazing too.

[crazyjr]

I gave up on trying to match scale to 1:1, if it were true, the weights and power would match up. We have bigger P/W and less weight compared to full scale

[suicideneil]

HP per metric ton is always a nice thing to know, but you need to have the rtr weight in lbs or kilos in order to calculate it:

3.5HP x weight in kilos
1000kg / weight in kilos = ??
?? x 3.5HP = ??? HP per ton.

Apparently though, speed doesnt scale like size does, theres some wonderfully tricky calculation to work it out instead...

[zeropointbug]

You gotta think cubic scale... all that matters is weight, but if you are thinking size wise then you go 5x5x5 = 125 times. (length x width x height) 3 dimensions

3.5hp = 437hp

The thing is, weight goes up at the cube of the size of an object.

[BL_RV0]

OHHHH that makes waaaayyyy more sense. I was wondering, how could a fullsize monster truck be 100lbs, have 10hp, and move at 400mph?

[zeropointbug]

lol, yah most ppl just forget about the dimension aspect of the calculation.

I think I am right... unless I am forgetting something as well.

[SpeedAssault]

Originally Posted by zeropointbug

You gotta think cubic scale... all that matters is weight, but if you are thinking size wise then you go 5x5x5 = 125 times. (length x width x height) 3 dimensions

3.5hp = 437hp

The thing is weight goes up at the cube of the size of an object.

WOW 437HP that's awesome ! that's 379 ft-lbs of torque , weight of 1250

how did you get 5x5x5 ?

[BrianG]

I'm not sure how the power would scale up, but the power:weight ratio seems reasonable.

For instance, take an 8th scale vahicle weighing 8lbs fully loaded with 1200w peak power. 1200w/8lbs=150w/lb. If a given 1:1 car weighs 3000lb, that's 450,000w, or 600HP.

Seems "low" until you remember torque is much higher in electric.

OK, most performance 1:1 cars can do around 150mph. That would be a 8th scale buggy geared for ~53mph. If I assume 100A draw (for max torque) on a 4s buggy with a Neu 1512/2.5d (fairly typical setup) I get 2.49ft-lbs of torque geared for that 53mph. That is a .311:1 ratio. On the same 3000lb car, that's 933ft-lbs of torque.

I'm sure it's more complicated than this, but it seems reasonable...

[zeropointbug]

Yah, and I think aerodynamic drag goes up at least by the square of the scale, but I am sure there are other factors like BrianG said, such as length, would affect the drag as well to a certain extent, and of course those HUGE wheels on our MT's/truggies and buggies.

"Seems "low" until you remember torque is much higher in electric. " BrianG -------- It's not that there is 'higher' torque, but it's that there is much more of it... over a very broad rpm range, and at 0 rpm, where it matters most.

I think we can assume that scale speeds and power to weight ratios don't match... obviously.

[Metallover]

Well there must be wayyy more scale torque because 1:1 cars have little 10" diffs and rc cars have HUGE scale diffs. And they still blow.

[zeropointbug]

Yeah, and the huge wheels and tires only make them bigger too... on-road cars have the largest diffs for their scale IMO, do they ever have diff problems?

I was just thinking, we can't really compare MT/truggies, buggies to scale because, well there is simple nothing full scale really to compare it with.

On-road cars, slash, etc. are the only vehicles we can compare though, how much HP do the full scale racing trucks have?... just to compare to the slash, which has what ~150watts?.... or 0.20hp

[BL_RV0]

You can compare MTs like the maxxes, savage etc