Sprocket size and motor torque

[bobdxcool]

I am trying to build a motorized cable drum which retracts the cable lying on the ground. I am using a 165rpm 1.3Nm (continuous torque) spur geared DC motor. I have a small sprocket (05-B1 standard, 22 teeth) connected to the motor shaft and have a bigger sprocket (05-B1 standard, 50 teeth) connected to the drum. A chain (05-B1 standard)is used to connect these two sprockets vertically and hence engage the motor with the drum. The diameter of the small sprocket is 50mm and the big sprocket is 125mm. The weight of the small sprocket and big sprockets are 200 and 500 grams respectively. The length of the chain is 900mm (8mm wide). The diameter of the drum is 200mm. The total weight of the cable that the drum must reel in is 5 kgs. Now, since the sprocket reduction reduction ratio is 2.27(50/22), the total torque available at the drum to pull the cable inside should be 1.3Nm x 2.27 which is 2.951Nm (29.51 kgcm). Is this calculation right ? Do I have to take any other factors into consideration here ?

Also, I believe this torque should be enough to pull the cable inside. If not I should either use a motor with higher torque or increase the number of teeth on the bigger sprocket so that the gear reduction ratio increases. Which among these two methods is recommended ?

PFA pictures of the whole system.

 

[desertfox]

Hi

Your calculation looks about right however what about the torque during start up when you have to accelerate the sprockets up to speed and also start the cable moving.
If the torque is insufficient I would try another speed reduction before going for a higher torque motor but bear in mind if you do this the time for the cable winding will increase.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[dvd]

Evaluate the overhung load capability of the motor shaft. The shaft may not be capable of handling the chain tension. Think about a jackshaft if necessary. This is a reversing drive. You need to assure that the chain is tensioned enough to not jump teeth on reversal. Your take-up will need to withstand tight-side tension during revere operation.