This page is to try and give people more of an insight into motors and which ones are commonly used along with their ratings and performance levels, this info is really only aimed at permanent magnet motors as they are the most common types.|
Firstly it is important to talk about startup currents, particularly when people want to use either an underrated controller or a petrol/diesel electric system:-
Most motors have a start up current of at least 3 times their rated current, simply put this means that if a motor is rated at 1HP the equivalent current at start up is equal to a 3HP motor. To work out the current you divide the wattage (remember 1HP = 746W, though most people call it 750W for simplification) by the voltage and then times by 3, this gives a good estimate on the start up current, so for a 24v 1Hp motor the rated current is 31.25amps which means the start up current is something like 93.75A which is why a 30A controller or alternator is not enough for a 1HP motor.
Here are the stall currents for our currently available motors:-
12v 150w motor ~35 amps
24v 750w motor - 220 amps (at 5 second stall)
As a rough guide each 100w of power will pull 135kg at 10mph on a reasonable track. (this is based on a 1HP (750w) motor pulling 1 ton at 10mph. This can be increased to around 180kg per 100 watt for 7-8mph running so below are the estimated figures for expected pulling performance:-
1x 150w motor 10mph = 202Kg 7mph = 270Kg
2x 150w motor 10mph = 405Kg 7mph = 540Kg
3x 150w motor 10mph = 607Kg 7mph = 810Kg
4x 150w motor 10mph = 810Kg 7mph = 1080Kg
1x 750w motor 10mph = 1012Kg 7mph = 1352Kg
2x 750w motor 10mph = 2025Kg 7mph = 2670Kg
3x 750w motor 10mph = 3036Kg 7mph = 4037Kg
4x 750w motor 10mph = 4050Kg 7mph = 5386Kg
We normally say that an 8 foot long coach is about 500Kg loaded and a 6 foot long coach is about 375Kg loaded.
Some motors such as the Sinclair C5 motors not only have a start up current of three times their rated current but the motor may also ask for more current which simply does nothing other than heat things up, this is called core saturation and makes it worthwhile having on ammeter on these motors, the Sinclair starts to saturate at around 60A and will continue to do so until at 120A.
Rated speeds and no load speeds, this is a key component to working out your maximum speed. Most motors are rated at their power level not at their no load speed (our motors we sell are rated at no load speed) which is fine for industrial applications or where the speed power level is needed however on railways we find that the motors are more than capable of exceeding their rated speed/power levels, indeed we rely on it for efficiency, as such to work out gearing you actually need to know the no load speed of the motor:-
All our 150w and 750w motors have a no load speed of 3000RPM
The Cinclair C5 has a no load speed of 3200RPM
The Bosch 1HP has a no load speed of 4200RPM
The reason the motors need to be geared for their no load speed is that they still have plenty of torque to increase the revs beyond their speed/power level, the beauty of this is that a motor is running at its most efficient when running as fast as possible. The other reason is that motors are rated at their voltage, normally 12,24 etc however most batteries are charged and running anywhere between 12.5 and 13.2V quite happily which means you actually have a voltage increase (and therefore speed increase) of 10% in most cases which gives the motors the extra power they need to go that bit faster into the no load speed.
Gearing, this can be a tricky area if you are not sure of what to do.
We find that on 8mm pitch chain and 3/8" pitch chain on a 3000RPM no load motor that an 8t on the motor and the biggest you can fit on the axle will give you 8mph for 8mm chain and 10mph for 3/8" chain, this is a very simple rule and works extremely effectively.
Motor speeds and gearing, the worst mistake you can make is to gear a motor for a speed higher than you want to run at. We come across a lot of people that say things like
"i'm running at 7mph so i will gear it to 10mph to give it some more on the hills"
NO this does not work, if you're car is struggling on a hill you drop a gear and raise the revs, that is exactly what a motor wants, spin them as fast as possible, so if your track speed is 7mph do your best to gear it for 7mph and this will add a lot of advantages such as:
Extended battery life, the motor isn't having to work as hard so not as much current is needed which transfers to longer running times or smaller less expensive batteries.
Better start up torque for pulling, If the motor is geared for slower top speed the pay off is more start up torque so you can get bigger loads moving.
Extended motor life, if a motor is having a hard time and is continually pushed to its limits it will burn out a lot quicker than a motor which is having an easier life.
Motors work by having two magnetic forces (one from the built in magnets and one from the current you are supplying) working against each other, if the two forces are too large for too long then they weaken each other, since the magnetic force we apply is through an electromagnet this won't weaken it is the magnets which are weakened resulting in larger current consumption and higher rmotor speed with less torque and power.
Continuous speed, if a motor is running at its most efficient it will also have the best high speed pull which means it is much more likely to keep a load moving at the same speed and if the revs do drop off they drop into the power zone rather than out of it.
Better controller life, regardless of which controller you go for having a motor that is pulling too many amps will only damage a controller in the long run and on current limiting controllers it also means your speed is much more likely to drop off.