Question about AC motor specifications

[mathewfixit]

Sorry if this seems basic, but I am the only engineer at the company and I also have no practical knowledge of engineering, only academic.

I am trying to spec a motor for direct drive of a wheel about 9lbs and 18" Dia. They want it to turn at 1000 RPM. I have a bunch of questions.

I calculated the HP for turning to speed in a minute is 0.04 and that including air resistance and a Cd of 0.04 gives the total HP is 0.07. This (seems like a lot of air resistance ~0.3, but that isn't my main question.)

1) My first question is now that I have an HP spec and desired RPM how do I choose a motor.
They want it run off a regular AC mains outlet. and run for a max of an hour at 1000RPM.

2) It seems that this baldor motors might be appropriate. Comments?

3) What does the RPM rating mean? Is it the RPM the motor will rotate at unloaded?

3) Also, could you point me in the direction of good resources on how to control the motor to run closer to the RPM we need?
Thanks for your patience

 

[LittleInch]

There's a few things I've got issue with here.

1) a syncronous motor wants to get to it's speed in a few seconds. If your wheel is just spinning, then acceleration forces are probably your key power issues. If a motor doesn't speed up fast enough, it doesn't accelerate and "slips" a lot with over heating and lack of speed up.

2) "regular ac Mains socket" presumably means 220/240 v single phase, but at what frequency? You need to know and specify to a motor vendor.

That motor states 3 phase, but the data sheet seems to indicate 2 phase might be ok as well. Note it says "moderate"starting loads, but is not clear what that is. A 6 pole motor is noted.

3) If you want exact speed you need a variable frequency drive (vfd) to vary the frequency into the motor. All depends how accurate you need the 1000 to be.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[mathewfixit]

I am not sure how to respond to issue #1

1) a syncronous motor wants to get to it's speed in a few seconds. If your wheel is just spinning, then acceleration forces are probably your key power issues. If a motor doesn't speed up fast enough, it doesn't accelerate and "slips" a lot with over heating and lack of speed up.

#2 I thought that most household outlets in the states were 60Hz. So that is what I looked for in the motor.

#3 If i wanted +/- 5% tolerance on the RPM how do I do that?

 

[Latexman]

Red Flag one of your posts and specify the new title you want to change it to.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[LittleInch]

It all depends on the kinetic energy in your wheel and where the 9lbs is located - at the rim or further to the centre. Work out how much energy your wheel has at 1000 rpm and the work on the basis that that energy needs to be imparted into the wheel in about 5 seconds by the motor. The starting torque of your motor may be available from the supplier and you need to work out if it is enough to accelerate your wheel. That is your key load here as far as I can tell, not the running loads which appear to be very low.

What is this thing?

60htz is common, but so is 50 in Europe and many other countries.

+/- 5%, buy a vfd with that level of accuracy.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way