Help deciding on motor for moving 1500lb shaft...?

[zyborg]

I am working on an application that requires moving a shaft (the shaft is not where all the weight is of course--there is other stuff attached to the shaft) 45 degrees on either direction (clockwise and counter-clockwise), stopping can be achieved with the help of a mechanical stop. It is preferrable that there are no gears involved and that there are not many moving parts--prefer just magnetic force to move.

I guess the main issue here might be the type of motor (or other recommendation) to use since the unit that will be rotated is 1500lbs.

I will like to know hints on possiblities since most likely this will be a custom motor. I open to suggestions on books, articles, etc.

Since I don't know what type of motor to use, I have yet to figure out how to calculate torque/HP needed.

I'll appreciate your inputs...

 

[MikeHalloran]

For starters, you forgot to tell us how fast you want to move the shaft, the moment of inertia of the assembly, and how many times the mechanical stop needs to withstand a small car crashing into it.





Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[Barry1961]

Sounds like an interesting application. Calculating the size of motor to do this will be tough since it will be sized by starts per hour and starting torque only.

I would guess you are going to end up with some type of pancake motor. Kollmorgen has some fairly large pancake servos. I have seen some very large old pancake style AC motors on air compressors. Some of these would be probably 10 feet in diameter and have a stator less than 2 feet long. Tremendous torque at a low rpm, you might find a used one somewhere cheap.

As Mike said above this your device has a lot of inertia already and you are also going to have to stop the inertia of the rotor. If you go to

http://www.skadrives.com

there is a free excell download that has sheet for calculating the energy in a flywheel that might help you get started.

Barry1961

 

[zyborg]

Thank you for your feedback...

Hopefully, tonight I will get more data, so that, I can calculate the moment of inertia.

I had initially said that I need to rotate 45 degrees, but this is only on a special instance. The rest of the time, I have to rotate 90 degrees within 2 seconds. The frequency that I need to rotate is every 6 seconds (minimum). This is a preliminary requirement, so this timing may be changed to be slower if design constraints force me to.

Barry, I will checkout

http://www.skadrives.com

thanks...

I will be posting again as soon as I get more data...

If you guys think of any other good sources (web sites/books, etc.) let me know

 

[zyborg]

Guys,

Here is a preliminary moment of rotational inertia per the current design:

104 lb ft2


I look forward to a response from the bright people in this forum...

Thanks in advance...

 

[sreid]

Just to get the big picture of the requirements, suppose you accelerate 1/3 of the time, move at constant speed 1/3 of the time and decelerate 1/3 of the time (this approximates a parabolic optimum power loss move).

The peak velocity for a 90 degree (pi/2) move is

w = 1.177 rad/sec

The acceleration is

Alpha = w/t = 1.177 x 0.666 = 1.76 rad/sec^2

The inertia is

J = 104 lb-ft^2 / 32.2 ft/sec^2 = 3.32 lb-ft-sec^2

Torque = J x Alpha = 3.32 x 1.76 = 5.6 lb-ft

This is the minimum torque required. The actual torque must overcome friction and the move will have to be faster to allow for setteling time.

The good news is that the required torque is not that large and since the peak RPM is low you could use a motor with a high torque constant to keep the amplifier cost down.

To get an idea of the motor size, a 5 HP 1800 RPM motor developes 14 lb- ft of torque.

I would use a brushless servo motor with a high resolution encoder.

 

[zyborg]

sreid,

Thanks a lot for your feedback...

I will be reasearching some more with the info you gave me...

I will come back with questions later on...