×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

What size motor do i need?

What size motor do i need?

What size motor do i need?

(OP)
Hi, i have to spec a motor, what i need to know is how do i figure out there torque required? it is a vertical shaft, bearing a load of 4kg, load diamter is 100mm. motor run time per cycle is 30 sec, so it needs to start quick, and stop quick. Im limted to a 750W input supply. length of shaft approx 100mm. any help would be great

RE: What size motor do i need?

Others can answer better I'm sure, but some clarifications are in order.

The gravity weight of 4kg acts at a torque radius of 100mm, correct?
During this 30 seconds, do you expect roughly constant speed or roughly constant acceleration or something else? If constant speed, how long to reach the target speed? How long the total distance travelled in 30 seconds?

=====================================
(2B)+(2B)' ?

RE: What size motor do i need?

(OP)
yeah, say an rpm of aprrox 60rpm. as it will only have about 30 seconds for the cycle it needs to be up to spped relatively quickly. i'll be using a bevel gearbox as to allow vertical rotation and support to load. imwondering can i figure out the torque required just knowing the load mass(4kg) and radius of the load(50mm)? as in T=FxD (force by distance or is it diameter?)

RE: What size motor do i need?

Yes its force X radius however your torque will vary from zero when the load is at 6 or 12'oclock to a maximum at 3 and 9'oclock as it rotates.
You need to consider acceleration time for the motor to drive load at required velocity.

RE: What size motor do i need?

Quote:

yeah, say an rpm of aprrox 60rpm
Are you planning on using gears (maybe a motor with built-in gears)?

How often does the cycle repeat?

=====================================
(2B)+(2B)' ?

RE: What size motor do i need?

I'm sure you could do this, but a simplistic calculation is
Mass = 4kg
Weight = Mass*g = 39.2N
R = 0.1M
Torque = Weight*R = 3.92 N-m
Power = 2*Pi*Torque*Speed = 24.6 watts (using speed = 60rpm).

That is the just the power required to keep the weight moving at a constant speed (the easy part). Need to think about how much additional torque you need available to get proper acceleration as mentioned and consider duty cycle and other factors to come up with good solution. I'm not the right guy to select this motor.

=====================================
(2B)+(2B)' ?

RE: What size motor do i need?

(OP)
30 second cycles continuously, ideally upto speed in a second or so,60 rpm,built in gears will be the preffered option, the load force will be a constant, the part being placed is negligible. yeah its ensuring i have enough torque for start up i need to know. also,what about stopping?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources