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Sonam
12-17-2007, 11:35 AM
hi...

i have to make a screw jack for lifting a load of around 4.5 kg (external load + wt. of jack's links and platform + friction). I have to use a motor to rotate the screw at around 50-60 rpm using max 12 V DC supply only. I need to lift the load to a height of around 30 cm (+- 0.5 cm) and then bring it down. So i will need a high torque slow speed motor...

I can use a geared DC motor or a stepper motor... I have got a stepper motor for free from a friendly workshop... There is no label on the motor so I cant identify it...

These are the dimensions of the stepper motor i have:
Shape : square with side 41mm
Length : 45mm
Shaft dia : 5 mm
Shaft length : 25 mm on one side and 10 mm on other.
Wires : 6
Step : approx 3.5 degrees
Resistance between Common and other terminals : 20.2 ohms

Please help:
1. Which motor to use : DC Geared or Stepper (or maybe universal???)
2. Contacts for getting these motors in Pune or Ahmedabad
3. Circuit diagrams

debu
12-17-2007, 01:09 PM
@Sonam: No question about it. Use DC Geared Motors. A DC geared motor of the same size, and same weight as a Stepper gives many more times the torque, as the stepper.

MohitM
12-17-2007, 06:55 PM
You could also use servo motors used in servo-stablizers. These may be cheaper than DC geared motors. High torque and move painfully slow as well. Should suit you.

allbits
12-17-2007, 08:05 PM
Forget Stepper!!

Hmm 4.5Kg @12 V....

Is this 4.5Kg the required final weight?? The exact torque will depend on the pitch of your screw. The lesser the pitch, the lesser is the torque required, and the trade off will be the speed.

Are there any speed requirements??

Geared Motors are the best bet, but you need to calculate the torque required by the motor, in Kg-cm, and look for a motor of that spec. That simply means, the motor torque required WONT be 4.5 Kgcm.

also, 4.5Kg means more than 1A, which means the coil resistance should be approx (R=V/I)

If I have the money, i would always go for a modified servo with a higher torque.. Eventhough you may not really need one.

Sonam
12-18-2007, 01:38 PM
4.5 kg is just the max weight we have calculated... actual would be around 3.5 to 4 kgs.

the screw will be parallel to the ground... it will be a long bolt which will be coupled to the motor... so we will buy the bolt with the least pitch available...

there r no speed requirements as such... since it is turning the screw, it should be slow...

these r the drawings we have made in autocad... the red cube is the motor connected to the screw...

http://s2.largeimagehost.com/TN/UeXeeFs/tn_jack1.JPG (http://s2.largeimagehost.com/img/untilted/UeXeeFh/jack1.JPG.html)
http://s2.largeimagehost.com/TN/UeXeeUF/tn_jack2.JPG (http://s2.largeimagehost.com/img/untilted/UeXeeFt/jack2.JPG.html)

praghu_cool
12-18-2007, 03:02 PM
hi ..,
forget about stepper as they won't give torque ., also servo as they are costly .
DC geared are the best for Ur application , you can also use PWM if you want speed control ...