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Figuring out a motor for a potter's wheel 
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#1
May1111, 02:24 AM

P: 1

I am trying to determine what the best motor would be for me to achieve an rpm from 0250 with a maximum 50lb load that is reversible and controllable. I heard DC motors are more variablespeed friendly. If I do need a DC motor, what type AC/DC power supply would I need?
Thanks, Neil 


#2
May1111, 12:42 PM

Sci Advisor
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PF Gold
P: 12,163

I reckon the best way to find out the answer would be to look at adverts or ring manufacturers and ask what power of motor they use. You can always ask something innocuous like "is the motor powerful enough?". That should get the right response out of them.
The quietest motors tend to be induction motors but they are difficult for speed control. Is speed control really necessary? I just found this infohttp://www.kilns.co.uk/productcategory.aspx?id=110 which implies that 1/2 or 1/3 hp motor is what you need. 


#3
May1111, 03:55 PM

P: 23

sophiecentaur's right. If you have a potter's supply in town, just go down and see what motor they have in the units they're selling. The manufacturer has done the research for you!



#4
Feb2112, 03:26 AM

P: 14

Figuring out a motor for a potter's wheel
i dont know if this the right place for this queston by ill put it anyways
in an electric motor (ac) with given volts, amps and max rpm (im guessing its max rpm that the specs give in a electric motor) how does the quantity of max rpm change? will it go up or down or neither if you increase the inertia of the "flywheel" (from say a aluminum or cabon saw to a grinding stone) will it just take longer to reach that max rpm with more inertia at the flywheel? i know net torque applied to inertia causes ang. acceleration the bigger the inertia with same net torque the smaller the accel. im guessing that the machine wont "know" that you switched from the aluminum saw to the grinding stone (or heavier flywheel) and stillapply the same net torque on the fly wheel, but for a longer period to reach that max rpm. correct me if im wrong . also do electric motors "know" when theyve reached max rpms ? for example electric saw motors and then stop accelerating? and about also what torque is calculated by formula hp=(torque(rpm))/5252? is it full load torque, accelerating torque, locked rotor torque or what? thanks. 


#5
Feb2112, 04:21 AM

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P: 12,163

Power is torque times angular speed  as you say.
Also, just as Force equals Mass times Acceleration (Newton's Laws), you also have Torque equals Moment of Inertia times Angular Acceleration  which you also described. Those are the basic definitions. That means that, a given power of motor / transmission system will produce high torque at low speed or low torque at high speed (basic principle of car gears etc.) Also, for a given torque, the acceleration for a high MI will be less than for a low MI (Obvious really) Things are not quite the same for Induction Motors but the following applies to most electric motors. An electric motor tends to produce higher torque at low speed (max when stalled, in many cases) because the current is highest. Eventually, a motor will reach a speed where the power it's delivering is limited by the torque. Because the rotation will produce a 'back emf', the current will drop off to near zero and the motor may go at high speed with very low power, only limited by the friction in the system. The problem is that, because there isn't just one value of torque to consider  it changes as the thing accelerates  there isn't a simple answer to any of these questions. There are two aspects to most motor applications. You need to know how quickly you want it to reach operating speed and also you need to know how much mechanical power is needed when it's running (rate of cutting / grinding etc.). In your case, no significant work is done, once it is up to speed,  just the energy needed to rearrange the gloop in the drum. You don't even want the acceleration to be too high. The motor requirements are not great (less than for a Potter, in fact). You will need some facility for speed control though. Almost any fractional hp motor would do, I suggest. You would just need an appropriate transmission (belt /pulley) system to get the speed range right and motors have their normal running speed marked on them, usually. "what torque is calculated by formula hp=(torque(rpm))/5252? is it full load torque, accelerating torque, locked rotor torque or what? " The formula applies for all speeds (except zero  when there is NO Power delivered, just wasted as the thing frazzles). Torque and Power would be specified for normal running revs, I should imagine) You need to specify two of the three quantities in that formula in order to find the third  which is a bit confusing because the torque from any motor is not constant with speed. I am still concerned about your ideas for suspension. I think you need to reconsider why you think hanging the drum is preferable. I think you may be thinking too subjectively. Look around you at other spinning machinery. How many examples are there of hanging systems? There must be a good reason for it. Consider washing machines  the best ones for water extraction are top loaders, with the drum supported at the bottom. Imagine the problems involved in doing the same thing with the drum hanging. You'd need all that stabilising concrete to be fixed to the ceiling!!! And you DO need an (ideally) infinitely massive support for stability and to counter any possible imbalance effects. I seriously cannot imagine it somehow automatically centring itself up, just by hanging there. 


#6
Feb2212, 01:14 AM

P: 26

If your just wanting to build a potter's wheel find an old electric treadmill in the paper or someplace like craigslist and take the motor, pulley drive and belt from it. If you get lucky you might find one where the controller works.
That will be normally about a 12 hp motor and will have no problems spinning the load you asked for using the pulley and belt designed for it. Surplus controllers for them are not expensive. You will then be able to adjust the speed to what ever you want within the motors rpm range. 


#7
Feb2612, 12:59 AM

P: 14

" Eventually, a motor will reach a speed where the power it's delivering is limited by the torque. Because the rotation will produce a 'back emf', the current will drop off to near zero and the motor may go at high speed with very low power, only limited by the friction in the system." what torque the acceler4ating torque or the given torque for the motor or stalled torque which one?? so will the max rpm change with larger/heavier flywheel? i know that the ang accel will be the motors torq divided by the MI (τ/MI)=α and this will help determine time to reach final ang vel. but what i dont know is if the fly wheel changed weight,.. will the target rpm still be the specified max rpm of the motor or will it be less or more? am still concerned about your ideas for suspension. I think you need to reconsider why you think hanging the drum is preferable. I think you may be thinking too subjectively. Look around you at other spinning machinery. How many examples are there of hanging systems? There must be a good reason for it. Consider washing machines  the best ones for water extraction are top loaders, with the drum supported at the bottom. Imagine the problems involved in doing the same thing with the drum hanging. You'd need all that stabilising concrete to be fixed to the ceiling!!! And you DO need an (ideally) infinitely massive support for stability and to counter any possible imbalance effects. I seriously cannot imagine it somehow automatically centring itself up, just by hanging there.[/QUOTE] i dont know if that was for me but im not talking aboun no hanging drum..im talking about a electric saw the type you plug to the wall 120V 12amps with a disk as a flywheel. thanks for the help 


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