Motor sizes and Watts

[BShady]

Hello

Can someone explain to me how size of motor makes a difference? Some small 50mm RC motors have basically the same specs as the large motors?

What does wattage mean in the motor ratings and how does it make a difference? ( large wattage vs lower wattage)

Thanks

 

[friendly1uk]

A smaller motor can often produce the same power as a larger one, but will over heat sooner.

Watts is one of the 3 basic electrical measurements. First you learn volts, then amps, then watts. It is foundation level. While I could try and tell you, it is better to get your foundations from proper learning resources. You need firm foundations if you want to build upon them.

loosely put, watts is power. The work done as a result of volts and amps. Either more volts or more amps will lead to more power (measured in watts). 500w is twice the power of 250w no matter how the watts were achieved.

 

[Miles]

Motor size is more or less proportional to torque capability.

For a given continuous output wattage you can use a smaller motor by reducing torque and increasing shaft speed.

Larger motors have greater thermal inertia and can be run at higher than the continuous rating for longer than smaller motors. Smaller motors have the advantage in surface area to volume ratio, though.

 

[BShady]

So if someone is building a large EV he can use small RC motors to run it instead of the big brushed ones? Based they they have the same specs.
How do you know what wattage motor you'll need for you EV?

 

[amberwolf]

How do you know what wattage motor you'll need for you EV?

You need to know the same things you would for a bicycle:

terrain
max speed
air resistance of vehicle
mass of vehicle
how quickly you want it to reach a particular speed
how long do you need it to stay at max speed
if going direct drive, size of wheels directly determines "gearing" ratio
if not, then you need to know what gearing you'll use
and probably some other things.

There are simulators for various types of vehicles around the web, and most of them will give you a wattage figure for various conditions. some of the simiulators are listed on the wiki.

 

[amberwolf]

Yes it does not worth to take the study of an engineer electrician so to have the knowledge to design an ebike.
In this case you will have to trust other engineers who made their mind that 250W is enough for moving a bicycle.
If those 250W seems poor to you, you do not need a 500W motor over a bicycle but a true motorcycle.

Yet more opinions that are overgeneralizations and wrong for many situations outside what you may be imagining.

There is also nothing here that I can see to say if he is speaking of a bicycle, or any other two-wheeled vehicle. Perhaps he is talking about a car, truck, golfcart, boat, plane, helicopter, or unicycle?


I think that you may be better off not posting when what you have to say is not applicable to the situation, or when you do not know what the situation is yet.

 

[BShady]

I am looking into building a go-kart. It should weight around 100lb. I didn't decide yet whether I'm going to do direct drive or not. I plan in useing a 12s lipo (50v) and want top speeds of 30mph on flat surfaces. I will be riding some off road as well. That's all I know.

What motor do you guys think is suitable for this build? I'm just trying to learn as I build so I know for future times.

 

[Hummina Shadeeba]

There's cool car starter motors on youtube! I found a starter motor. There's also guides to doing out there. My attempt stopped when I couldn't turn a single screw to open te motor an see what's inside

Pure conduction motor so no magnets an huge power. But does get hot quickly. Good for short fast runs. Not sure about what controller u could use as lots of people seem to simply have off and on full.

What u folk think of the car starter motors and what limitations do they have? Pretty easy to come by and I like the idea of a conduction motor

 

[Skalabala]

There's cool car starter motors on youtube! I found a starter motor. There's also guides to doing out there. My attempt stopped when I couldn't turn a single screw to open te motor an see what's inside

Pure conduction motor so no magnets an huge power. But does get hot quickly. Good for short fast runs. Not sure about what controller u could use as lots of people seem to simply have off and on full.

What u folk think of the car starter motors and what limitations do they have? Pretty easy to come by and I like the idea of a conduction motor

90% of the power induced into a starter motor goes to heat energy :lol:
They should have ferrite magnets in them.

BShady, see if you can find an electric scooter with dead batteries for cheap on your local (junkmail/craiglist)
Then you have a motor with torque and a controller with throttle