What is horsepower, and how can I use this measurement to calculate if I can move something at a specific rpm?

Atreyo Bhattacharjee

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First, I'm sorry if this is the wrong subject to post this under, and for how long and convoluted the tile was. Let me explain.

I'm building an electric scooter with my friends, and I was surfing Google for electric motors. This is the one I plan to purchase:
http://

I understand torque is rotational force at a distance, so 1 pound-foot would mean a rotational force able to move 1 pound, when the mass is 1 foot away from the center. I also understand horsepower is torque over time, so 1 horsepower is approximately 550 pound feet per second. But how does RPM fit into all this? If a motor has 1 horsepower, at 60 rpm, does that mean it is twisting with 550 pound feet of torque, for every second in it 60 rpm, so in every rotation, it has generated 550 pound feet of torque? I'm fairly new to engineering, and I my question really is, how can I use measurements of torque, RPM, power, or whatever else to tell if a motor can accomplish something, whether that be rotating something very rapidly, or pulling something very heavy.
 

USAFRet

Titan
Moderator
If geared properly, that motor would power a scooter. For about 5 minutes.
You also have to take power consumption into account. That thing is meant to run a treadmill, plugged into the wall, not on battery.

Don't reinvent the wheel.
Find a current scooter. You can probably find a broken one for free. See what motor and battery it uses.
 

Doctor Rob

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Jul 21, 2008
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from what I know.. not sure how to convert that.. but it would be SUPER overkill and require a LOT of batteries.. 130Volts DC requiring 2,611Watts.. unless you had a converter and had it plugged into an AC outlet all the time you would NOT get any distance, or power out of it.. as a lot of motors can run at a lower voltage / wattage but then you get very little torque out of them.

IF you are building an scooter for them to ride on.. 2 wheel or something like that.. Or maybe you are talking about maybe an powered wheel chair or something like that. I would still look at motors made for electric bikes and such.. a LOT less power requirements but still plenty of power if you need it. Brushless motors are the way to go if you want longevity out of them (quieter as well) and they use less power to go the same distance as a brushed motor.. 48V are nice if you need to pull / push a heavy person or 36 if you don't need to move a heavy person. IF you go brush-less you normally need a speed controller though just an FYI becase brushless motors are by nature a little more complicated as they are normally multi phase (so you have more then 1 positive post.. and they provide the power at different times sorta like a gas engion that has more then 1 cylinder.. one fires, then the next then next and so on.. it saves on power that and so on..

 

Doctor Rob

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lol not sure about 5 minutes.. you would Need to have a car sized battery bank :) to power it at 130V and over 2K watts.. so thats like 10 or 11 large deep cycle batteries at like 1K in cost to get that 5 minutes or so of use.. or like 10K in cost do to lithium..
 

Atreyo Bhattacharjee

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Feb 7, 2017
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Ok, but would you explain HP and RPM, and how they relate to each other? I now see this is impractical to power a scooter, but just for future reference. I've looked online, and at videos, but all I've seen are explaining it at an amount of work (torque) over a time. How does RPM come into this?
 

Doctor Rob

Distinguished
Jul 21, 2008
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from what I know.. not sure how to convert that.. but it would be SUPER overkill and require a LOT of batteries.. 130Volts DC requiring 2,611Watts.. unless you had a converter and had it plugged into an AC outlet all the time you would NOT get any distance, or power out of it.. as a lot of motors can run at a lower voltage / wattage but then you get very little torque out of them.

IF you are building an scooter for them to ride on.. 2 wheel or something like that.. Or maybe you are talking about maybe an powered wheel chair or something like that. I would still look at motors made for electric bikes and such.. a LOT less power requirements but still plenty of power if you need it. Brushless motors are the way to go if you want longevity out of them (quieter as well) and they use less power to go the same distance as a brushed motor.. 48V are nice if you need to pull / push a heavy person or 36 if you don't need to move a heavy person. IF you go brush-less you normally need a speed controller though just an FYI becase brushless motors are by nature a little more complicated as they are normally multi phase (so you have more then 1 positive post.. and they provide the power at different times sorta like a gas engion that has more then 1 cylinder.. one fires, then the next then next and so on.. it saves on power that and so on..

you can do something like this
https://www.ebay.com/itm/1000-W-48V-DC-electric-motor-kit-w-base-speed-controller-Foot-Pedal-Throttle-/161881448993

but the batteries are not cheap if you go with good lithium ion ones..
 

USAFRet

Titan
Moderator


RPM is not really relevant.
Your PC fan can spin at 3000RPM. Put wheels on it, and it couldn't haul a dead mouse. Too much load.
A truck engine will also spin at 3000RPM. And can move several thousand kilos down the road at 80mph.

Which is where horsepower comes in.
 

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