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Hi guys,

Just a bit of physics for calculating specs on your electro motor.
In the end we will end up with some very handy formulas that I will highlight in blue.
The first (well known) one :

Power (W) = Voltage (V) * Current (A)

W = Watt
V = Volt
A = Amp

Tamiya Dirt Tuned Info Conversion calculator

Rpm = 17,000 (at 7.2V)
Torque = 380 g-cm

Calculated :

Power = 66W
Current drain = 9.2A

Mmm... theoretically not better than the 23T Yeah Racing.
It is mentioned that this is at it's best efficiency. I'll have to see if that should be calculated in the power and drain...

I've always had trouble understanding if these numbers actually mean anything, whether they're just for comparison, or just hype.
eg we've calculated power using the manufacturer's rpm figure & the motor's rated voltage, but do we know if that rpm is what the motor's doing when you feed it with the 7.2V rated (Nominal) voltage, or what it does when you plug a '7.2V' battery into it (A charged 7.2V no-load volts is usually around 11.5V). Also, don't forget the voltage under load will 'wander', being influenced by how much current your battery can REALLY supply, temperature & resistance of the windings AND the actual rpm the motor's doing when you measure it.
The biggest nail is when you consider that a motor makes it's maximum torque at zero rpm, the least torque at it's flat out speed, the flat out speed being determined mostly by the voltage & current you can supply it with, but also limited by bearing friction & rotor wind-drag, not to mention whether or not your car's set up with optimum gearing...
Consider a 'high power' race motor. It'll always draw lots of current (Because less turns means less resistance, meaning it'll pass more current) & in doing so, drop the instantaneous battery voltage considerably. It will 'want' to rev high too, if you let it. If you put too large a pinion on it, it will never 'rev out' to its maximum rpm, it will use high current & get hot trying to go as fast as it wants. Meanwhile, you'll be overtaken by matey with a stock 27t, revving at half the rpm, using less current & barely dropping the battery voltage, all because his gearing is better matched than yours.
Batteries - yep I'm sure LiPos will deliver 16.5A, but for how long before they self-destruct? A new, fully charged NiCd pack MIGHT manage 16.5A briefly, but not for the duration of a race methinks. From what I've seen, a NimH won't supply that kind of current, full stop.
In summary, you can influence how well your toy car goes far more by setting it up right than by going on manufacturer's claimed 'motor performance' numbers

The motor is just a part of the whole system of course...
But it's always interesting to know the theoretical specs.
Practice'll tell much more though.

Don't really get how any rpm could be before efficiency.

17T LRP-HPI Challenge Motor (my favourite) info

Rpm = 31000
Power = 185W

Calculated :

Torque = 581 g-cm
Current = 25,7A

Just another nail... this is only considering the electrics too, it doesn't really cover the magnet power, which can affect motor performance for AND against. ie unless you're measuring actual torque at the spindle, a lot of the inputted power can be wasted overcoming magnetism of soopa doopa magnets if the motor isn't running at the specific speed that the magnets are timed (angular position) for. By the same token, if the magnets are weak (Or mis-timed) all the inputted power going to making electromagnetism in the rotor won't mean a thing if the opposing poles of the permanent magnets aren't managing equal force - the current will be just wazzing around the coils & doing nothing.
Here's a good one for you - just retrieved an old 27t motor with a label on it...
rpm: 21192 @ 5V
power: 58W @ 10900
efficiency: 43.8% @ 13900
torque: 92.4Nmm
Are these the best/maximum ratings?
So, if you want max rpm, feed it 5V?
if you want max power, only let it rev to 10900? (Beyond that magnetism is counter-productive?)
is the efficiency stated the best? Bit poo if maximum efficiency is at half speed...
In the real world though, this motor goes like hot snot, cooks the batteries & gives 3-5 mins run time on SCR1400 NiCds. My 'no limit' LRP ESC can't cope with it & keeps shutting down. It makes the wiring hot too.
I also have a modified 17t ballraced double-wind - same run time, no problem with ESC, & nowhere near as quick.
Main difference between the 2 motors is that the 27t has rare-earth (strong) magnets, lightened rotor & 'lay down' brushes (Can transfer current to the rotor better)

If my conversion's right, 92.4Nmm is 942gcm. My 27t is supposedly making nearly double the torque of your 17t (Thats unlikely), using only 1/3 the power at 1/3 the rpm, despite being only 44% efficient.... more than convinced these numbers don't mean anything now, the manufacturers are just putting them there to impress you & make you buy their motors!

The motor can be run with higher currencies then the are designed for, it's the amount of amps they draw that generates the heating in the wires and burns down esc (whenthey get too high).
Also the magnets and windings matter and the can size the motor has strong effect on the momentum in the motor.

Interesting... these I think are "real" measurements - with load :

power: 58W @ 10900
efficiency: 43.8% @ 13900

The first one gives a torque of 518 g-cm in the second formula, leading to an efficiency of 55% compared to what's given.
Makes me think the maximum rpm under load is 13900, with a (lowest) 43.8% effiency.

The 21192 must be the max rpm without load... theoretical so to say, done at 5V.
But then I hit a bump trying to calculate :

P = V * i
P = T * rpm * 0.00001027

V * i = T * rpm * 0.00001027
5 * i = 942 * 21192 * 0.00001027

i = 41A and P = 205W
Current 41A and Power 205W

Which seems to be a factor 2 too high...

The specs of the LRP are also without load btw. I suspect the efficiency to be around 80%...

Rpm = 24800
Power = 148W
Torque = 465 g-cm

I think current drain is the only one without an efficiency factor...
Eddrick's motor - I'm guessing the torque was theoretically calculated from the max rpm without load by the factory?