# Thread: To design a pulley system driven by a motor

1. ## To design a pulley system driven by a motor

Hi everyone,

I want to design a pulley system driven by a motor to pull a rail assembly with a constant speed. I am not sure how to begin ?. As of now I thought of the system with one moving pulley connected to motor and other fixed pulley connected to the rail via rope. The whole system is close loop so that as it sliding forward , it can also slide backwards. I am not sure how much length of the rope I require , what should be the optimal diameter of pulley .
Following are the specifications of motor which I will be using :
Power = 40 w ,
(90~1700 r/min)

2. Manjul,

This may best be posted in "Linear and Rotary Motion" under "Mechanical Engineering".

You didn't give much information...
How much travel will there be?
How much weight are you moving?
How fast does it need to move?

You might take a look at the method used in some older photo copiers and flat bed scanners for moving the scan head/lamp assembly. They used a small drum with plastic coated steel cable wrapped around it attached at the center. With a couple of wraps from the center of the drum on one side, the cable then extends the length of the bed, around a pully, and back to the scanner head positioned near the drum. Many wraps (just a bit longer than the travel) are wrapped from the center on the other side, and then attached to the scanner head. Turning the drum moves the scan head. The cable on the drum does not over lap, just a single layer.

I scrapped a tape archive library machine that used this method for linear motion in both X and Y axis. The motors and drums were stationairy.

Steve

3. Hey Steve,

I am sorry for not replying earlier. The length over which the rails can slide is 80 inches. The weight that I need to move with the help of motor is around 18 kilograms. The speed with which the rail has to move is in the range of 0.1-0.4 m/s.

I would really appreciate if you help me . I am confused as to what all forces I need to consider. What is the length of rope I need to use? I can attach the solid works drawing of the system to help explain the things more clearly.

Let me know if you like to see a solid works drawing.

Thanks,
Manjul
Tc

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