help determining AC motor

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treeman
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help determining AC motor

Post by treeman » Mon Mar 28, 2005 12:57 pm

I am designing a 3 dof motion platform similar
to the one on this link. As I am not a physics major I need some help determining motor torque
speed hp etc.. any help would be great.<p>thanks<p>steve>simulator<p>[ March 28, 2005: Message edited by: treeman ]</p>

terri
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Re: help determining AC motor

Post by terri » Tue Mar 29, 2005 9:19 pm

Why don't you contact them and ask?<p>http://aerosim.calpoly.edu/contactus.html<p>Theirs seems to be big enough to hold two people. A lot depends on how big a mass you're going to put on your platform and how fast you want to move (rotate) and reverse the mass, etc.<p>You could probably find out what mass and dimensions they at Cal Poly had planned on, and what size/type motors they used, and scale yours up or down from there.<p>Would a surplus "cowboy-bar" buckin' bronc or bull amusement ride do it for you without too much expense? Enzo, of this board, seems to be involved in amusement/vending machines and he might be able to help you find a bull ride machine if you contact him. See the "MINATURE GOLF WINDMILL" topic in the "General" category. It may be a few pages back by now.<p>Do you really need 3 degrees of freedom? Maybe a paint can mixer-upper would do. <p>Or a ride in my '85 Chevy.<p>[ March 29, 2005: Message edited by: terri ]</p>
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Chris Smith
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Re: help determining AC motor

Post by Chris Smith » Tue Mar 29, 2005 9:48 pm

Some rough figures from many many years ago was one HP could lift 1700 pounds?, one foot, in a minute. Check on these numbers but....<p>The math can be divided, and roughly calculated in any direction for the variable of time, or distance, or weight. <p>1700 [unit pounds] x one [unit time] x one [unit distance]

In other words, first take in mechanical loss from a oil driven pump at say 33 percent loss,.....<p>..... and then 1700 is [one] times [one], which means that 2 feet is a division of 1/2, [1700 x ½ x one] and thirty seconds is another half, [1700 x ½ x 1/2] so that you divy up your travel, how fast [time] and put it into the basic figure and then for good measure, increase your HP some more, or round it off to the nearest higher HP figure. <p>
So if you need three feet of movement, [x 3] at one second, [x 60] and 200 pounds [X 11% ]
its roughly 21.17 hp with out mechanical loss. <p>7 hp for mechanical loss, and some more for added margin. ~30 hp? <p>Double check ALL the figures including the original HP figure?

terri
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Re: help determining AC motor

Post by terri » Wed Mar 30, 2005 5:45 am

Hmmmm.... I don't know. Just eyeballing those motor/transmission assemblies in the link, they sure don't look like any 30 hp, or even 10 hp each. They look more like maybe 2 hp each, if that much.<p>Plus, the lines going to the machine don't look big enough to be hydraulic lines transmitting that much hp (Chris Smith's 30 hp) from outside pumps as a power source if they are hydraulic motors.<p>And one hp is 33,000 ft-lb per minute, not 1700.<p>Again, this question's answer depends on starting parameters: How much, how fast, how big, how come? <p>I again recommend that treeman contact Cal Poly directly and scale his intended platform/shaker/paint-mixer/whatever from their numbers.<p>
LATER ADDENDUM:<p>Nuts. I decided to do your homework for you. I sent the following message to "S. Kubic" at Cal Poly:<p>---------
Good morning, Mr. Kubic!<p>I wonder if you could look over this topic from the NUTSVOLTS.COM electronics forum and offer your comments:<p>http://206.131.241.58/ubbcgi/ultimatebb ... 1&t=002701<p>No need to respond to me directly. If you can offer some starting parameters for this questioner, it would be appreciated.<p>Many thanks,<p>terri wd0edw<p>[ March 30, 2005: Message edited by: terri ]</p>
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haklesup
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Re: help determining AC motor

Post by haklesup » Wed Mar 30, 2005 6:38 am

looks like they used geared stepper motors (possibly servos) based on one controller per motor. For a stepper motor, torque is constant with speed.<p>When you shop for motors, the torque will be specified, a gear box will reduce the speed and increase the torque by the gear ratio (half the speed, twice the torque). If you sacrifice speed, you can do it with a smaller motor. Speed and direction is determined by the input you provide the controller.<p>Expect to spend several hunderd $ for each heavy duty stepper and controller. THe thing probably needs quite a bit of current too so throw in a 50A DC supply. Unless you can find the stuff on the surplus market. Building prototypes is rarely cheap.<p>Since the imperial unit of torque is foot-pounds (I prefer this over metric Newton-Meters), it is relatively easy to calculate how much torque you have based on the length of the lever arm attached to the motor shaft. This force is applied to the end of the lever arm. Any other mechanical means (the platform) attached to that may modify the force seen by the load.<p>To calculate the force needed to hold the platform in one place you use techniques of Statics (F=MG) but when you move it around, momentum comes into play and you need to concider dynamic calculations (f=MA)<p>Force, mass, gravity, acceleration<p>If you over-design the power of the motors, you won't have to worry about any calculations. Math is needed only if you want to engineer the components to match the requirements precisely or to determine minimum specs. (an over designed platform could feature an ejector seat function)<p>Is your application gaming as it is in the calpoly examples? You'd think they would at least weld a bucket seat on the thing or something.

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Re: help determining AC motor

Post by terri » Wed Mar 30, 2005 8:40 am

hacklesup: "an over designed platform could feature an ejector seat function"<p> :) Very good!<p>However, an AC motor was specified originally. I only mentioned hydraulic motors in case Cal Poly might have used them. But, Cf above, the pics don't indicate this.<p>S. Kubic, where are you?<p>[ March 30, 2005: Message edited by: terri ]</p>
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Chris Smith
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Re: help determining AC motor

Post by Chris Smith » Wed Mar 30, 2005 2:40 pm

If 33,000 is the figure, divide by 19.4. <p>The math is still the same.

treeman
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Re: help determining AC motor

Post by treeman » Wed Mar 30, 2005 7:17 pm

Thanks for all the help. I spoke with the man
who built this system on the phone last year.
he did tell me that the motors were 3 hp ac
motors but he would not give me specifics.
he is using a motion control card and 5 hp
magnetek gpd515 drives. This system is actually
a 3 phase system designed to run on a standard
wall outlet. Mr barry is in business to make
money so he wont give me too many details and
I respect that. Im just building one for fun
as I feel the $25,000 price tag is a bit steep.
I am building this motion platform for a popular
nascar racing sim. for the pc. So the kids and I
can really geek out! lol I am an self employed
arborist from Waterford CT for those who were curious. Thank-you all and anymore Ideas are
welcome. I have about 2 years of off and on
research into this and Im finnally going to
get this thing together!!!

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haklesup
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Re: help determining AC motor

Post by haklesup » Wed Mar 30, 2005 8:48 pm

$25K The NRE will get you every time. Looks like they still have $5K to $10k in materials.<p>AC motor is pretty ambiguous, that term covers a lot of ground. All it tells me is that the controller plugs into the wall. I think the point being made is that it is not hydrolic or pneumatic. <p>I've been imagining a 2dof platform for some time that consists of a platform mounted on a half sphere made of steel tube or an old satellite dish (probably too weak and not really a hemisphere) and resting on a base with rollers that support all of the weight. <p>Two motors (X and Y) in the base rotate the hemisphere forward and back and side to side via rubber wheels. A third DOF could be added directly inder a seat mounted on the platform(a cam mounted on the shaft can be used to elevate the seat without any fancy gearing, belts etc.) <p>Conversely you could build a whole sphere and get inside. Upside-down would be possible with this config. Try interfacing to Roller coster tycoon for a real terror ride (bring a barf bag).<p>I've not worked out how to ensure the platform will not fall off the base though. (Imagine yourself strapped in the sphere rolling across the room uncontrolled)<p>The nice part of this design is that all of the weight is supported by passive rollers in the base. The motors only need to rotate the sphere and therefore can be selected smaller. It may not be as precise as the calpoly or other simulators but will still give you a heck of a ride.

treeman
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Re: help determining AC motor

Post by treeman » Wed Mar 30, 2005 9:16 pm

hey thats a kewl idea hehehe! I have a system
designed now using stepper motors and a motion
control card, card is in the mail now and
is expected here this weekend. for now im
going to set up the system using the steppers
and some linear actuators. I have a friend
that works for intelligent motion systems
and was able to get me the motors and drives
cheap, real cheap LOL the card i ordered was
about $400.00 going to get the steel next
week and get welding. Ill keep ya'll posted.
prolly post a few pix too.<p>[ March 30, 2005: Message edited by: treeman ]</p>

dart70ca
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Re: help determining AC motor

Post by dart70ca » Thu Oct 06, 2005 10:33 pm

Hi,
Just a newbie here but I might be able to help a little. Those are indeed regular 3phase motors. In the movies there you can see the 3 frequency drives in front of them, the controller module (I assume) is the smaller box between the drives. The motors (I'm pretty sure from the paint and markings) are Baldor units. They're C-face frames coupled to gearboxes. You can see the rotation sensors on the left side of the gearbox where the motor joins it, viewed from in front of the frequency drives. Baldor often supplies motors and gearboxes as matched units and, looking at the paint, there's a chance this might be the case. You could contact Baldor and they should be able to help you.
Hope this helps.<p> Keith

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Re: help determining AC motor

Post by rshayes » Fri Oct 07, 2005 12:42 am

I would suggest using a hydralic system for this type of application. Compared to the controller-motor-gearbox-lever system shown, a simple hydralic cylinder would be dirt cheap. Only one motor and pump assembly would be needed and this would probably be off the shelf.<p>In the system shown, holding the platform in a neutral position requires constant torque from all three motors. This could add up to a substantial amount of energy (ie light bill). If those are 3 horsepower motors, the peak power requirement would be in the order of 10 kilowatts. The "standard electrical outlet" that they refer to is probably 208 volt three-phase at something over 20 amps per phase. It may be standard in an industrial building, but I certainly don't have one at home.<p>The lever arm system delivers differing forces to the platform depending on the position of the lever arm and the current in the motor. In other words, it is a non-linear element in the control system. This can be compensated for with a computer as part of the control system at the expense of programming complexity. It also means that the gear ratio in the gearbox can only be chosen for an inertia match at one or two positions of the lever arms, and that accelleration will be less than optimum for other positions.<p>Actually, that platform looks very similar to the Link Trainer, which used pneumatic actuators. This was one of the earliest flight simulators. It was designed about 1931 and several thousand were built. It was fairly widely used for about 30 years. A few have actually been recently restored. Try a google search for "link trainer".

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