## torque for horizontal chain and sprocket drive

## torque for horizontal chain and sprocket drive

(OP)

Hi,

I have 4 vertical power screws which are all linked together by a horizontal chain and sprocket drive. So i have 4 sprockets of the same pitch diameter (one on each screw) and 1 chain (running on the periphery of all the the sprockets). There is a handwheel ontop one of the power screws, therefore turning the handwheel turns all the screws at the same time.

I am building a lifting device that uses these 4 power screws. I already calculated the torque required to lift the load to be 15 Nm. But my question is, how do i determine the maximum torque required to initiate the chain drive? Im sure the answer is really simple but i just dont see it.

There is no slack side on the chain, so my 1st instinct would be to take the intial tension on the chain and multiply it by the pitch diameter. then multiply this value by 4 to obtain my final value. is this correct? Or should i consider the final speed of the chain drive and the friction.

I would appreciate any suggestions

I have 4 vertical power screws which are all linked together by a horizontal chain and sprocket drive. So i have 4 sprockets of the same pitch diameter (one on each screw) and 1 chain (running on the periphery of all the the sprockets). There is a handwheel ontop one of the power screws, therefore turning the handwheel turns all the screws at the same time.

I am building a lifting device that uses these 4 power screws. I already calculated the torque required to lift the load to be 15 Nm. But my question is, how do i determine the maximum torque required to initiate the chain drive? Im sure the answer is really simple but i just dont see it.

There is no slack side on the chain, so my 1st instinct would be to take the intial tension on the chain and multiply it by the pitch diameter. then multiply this value by 4 to obtain my final value. is this correct? Or should i consider the final speed of the chain drive and the friction.

I would appreciate any suggestions

## RE: torque for horizontal chain and sprocket drive

You will have a slack side to the chain, it will be the span after your crank handle. Depending on the center distance between the power screws and how much your chain stretches you may have problems with the chain staying on the sprockets, particularly the span after the crank. You can make drawings which show the chain taut on all spans, but the chain is going to stretch and you will get a catenary sag that can cause the link plates on the chain to rub the sprockets and wear. You should consider chain tensioners on the spans adjacent to the crank handle, since this will be a reversing drive.

Also, depending on how you attach the power screws to the load you may end up with a lot higher torque requirement than you anticipated. (Assuming that you are locating a bearing very close to the sprockets so that the power screws don't deflect when you turn the crank.) If your sprocket bearing centers and the power screw centers are not matched very closely you will have high side loads applied through the nuts on the power screws, as I have experienced firsthand. Provide some type of floating attachment for the nuts and hopefully provide some type of linear guide besides the power screws.

## RE: torque for horizontal chain and sprocket drive

The power screws are all vertical. and will remain vertical during operation of the lift. Each power screw is braced at the top and near the bottom by radial ball bearings. The threaded length is between the two radial ball bearings, therefore any moments or deflection generated by the load is canceled out at the radial bearing supports. At the bottom of the power screws there are thrust bearings that supports the direct trust of the load. Now the chain and sprocket drive is between the lower radial and trust bearings. (5cm apart). Im hoping that the tension in the chain drive isnt so much as to rip trough the trust bearings or signficantly increase the final required torque. This is why i really have to know how to determine the maximum torque in the chain drive. Any ideas?

## RE: torque for horizontal chain and sprocket drive

## RE: torque for horizontal chain and sprocket drive

## RE: torque for horizontal chain and sprocket drive

As for the thrust bearing, are you going to lock the radial bearing to the shaft with a press fit or shaft collars or some other means? If so the radial bearing is going to see the thrust first, you could consider using a tapered roller bearing along with a shoulder on your power screws and eliminating the thrust bearing.

## RE: torque for horizontal chain and sprocket drive

RAVITEJA

DESIGN ENGINEER

HYDERABAD

## RE: torque for horizontal chain and sprocket drive

DVD, that torque is the torque required by the power screws and not the chain drive. The radial brgs have a sliding fit on the shaft and is press fitted to its housing. no need for tapered brgs.

I guess, it would be best to estimate the starting torque of the chain drive as the running torque

## RE: torque for horizontal chain and sprocket drive

## RE: torque for horizontal chain and sprocket drive

Regarding chain tension, it should have no effect on the torque required for the application, as long as bearings can handle the tension. If they can't, then you have other worries to think about. A large amount of slack will cause a bang and eventually break the chain.

Now for coming up with torque, we first need to calculate inertia. Why?

Acceleration Torque = inertia x rotational acceleration. (Most just think of force x radius)

Inertia Pulley: Jpulley

Wr^2

Jsprocket = ------

2g

Where:

Jsprocket = Inertia of Sprocket (lb-in-sec^2)

W = weight of sprocket

r = pitch radius of sprocket

g = gravity = 386 in/sec^2

---------------------------------------------

Inertia Chain: Jchain

Wr^2

Jchain = ------

g

Where:

Jchain = Inertia of Chain (lb-in-sec^2)

W = weight of chain

r = pitch radius of sprocket

g = gravity = 386 in/sec^2

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I need to run, I will finish my post later

Cameron Anderson - Sales & Applications Engineer

Aerotech, Inc. - www.aerotech.com

"Dedicated to the Science of Motion"