Gear Increaser Break Away Torque

[SKinzel]

Hello everybody,

I'm fairly new to the forum and have a question. A customer wants me to calculate the break away torque for a redesigned increasing gear drive. We are changing the ratio so he needs to select a new electric motor and this is the first time a customer has asked me for a break away torque.

I can calculate the WR^2 for both shafts but I'm not sure how to calculate what the break away torque for the reducer will be. With the input on the low speed shaft, would the break away torque be calculated using WR^2 referred to that shaft? WR^2 has units of lb-in^2 and torque has units of lb-in so I'm not sure how to find a torque from WR^2.

The unit has plain journal bearings so I imaging that will have some effect but I'm not sure if I need to consider that.

Any help is appreciated.

Stuart Kinzel

 

[SKinzel]

I guess I'm not the only one that can't find any information on making this calculation.

 

[electricpete]

I think friction is THE factor to determine breakaway torque and inertia is irrelevant.

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[rmw]

Electric pete is right.

I am familiar with electric actuators that use the internal friction to prevent back driving of the actuator when it reaches its commanded position. The motors of those drives obviously have not only to do the break away, but move the load as well, which deals with the inertia.

Point is, that it is the friction that prevents the back driving, and the motor has to overcome this before it can deal with any inertial loads.

rmw

 

[SKinzel]

So far this the only thing that I've been able to find

http://www.tech.plymouth.ac.uk/sme/desnotes/gears/gearaccel.htm

According to this my customer is going to need to supply me with an acceleration requirement. The low speed gear assembly is fairly large (3500 lbs.) so the friction component will probably be significant.

Thanks for the help. If I come across any additional information, I'll post it here.

Stuart