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BMU460SA-50A-3 Questions.

Posted: Sat Jun 07, 2014 1:30 pm
by cstmwrks
Currently I run at 2 speeds and on one of them i have the need to manually slow the motor down and then speed it back up. This has been done with a stepper motor controlled through a PC via keyboard commands.
I've been reading the manual on this BMU460SA-50A-3 system and it looks like a very promising replacement for my current control system.
If I understand correctly you can have 4 pre set rotation speeds / directions and can also vary the speed both up and down on the fly, correct?

Your info states a rated torque of 76 lb-in and a Permissible Load Inertia of 12000 oz-in². If I understand Permissible Load Inertia right, this would be how much of a work load is in the system that the motor is able to overcome to start rotation, correct? I've attempted to look up "oz-in²" to understand better if this value is greater than, or less than the motors rated torque of 76 lb-in. I've not had any luck. Would you be kind enough to clarify?

Also can the driver accept inputs from limit switches?

Thanks for the help.

Re: BMU460SA-50A-3 Questions.

Posted: Wed Jun 11, 2014 5:55 pm
by om_tech_support_JT
Hi cstmwrks,

Thank you for your interest in our new BMU series! Yes, the BMU series system is capable of varying speeds and it can also generate holding torque at the motor when stopped. However, since this is an electrical brake and not a mechanical brake like our electromagnetic brakes, if the power somehow fails, and you're lifting something with the motor, the load may drop thus causing safety issues. Our manual recommends against using the BMU series to move a load vertically for this reason. The gearhead will provide some holding torque but most likely not sufficient to hold your load. For vertical loads, we would suggest something more reliable like the BX, BLE, or BLV series brushless motor and controller systems which includes electromagnetic brake models.

Your understanding of inertia is correct. Inertia is a resistance to a change in speed. The motor has to overcome the inertia in order to start rotation, but the same effect also occurs during stopping.

76 lb-in is a torque unit. This means the motor can rotate 76 lbs if the load is 1" away from the motor shaft. 12,000 oz-in² is an inertia unit. These are treated differently in our literature. As long as your required torque stays under 76 lb-in, and your inertial load is under 12,000 oz-in², the motor will work. Inertia is used to calculate acceleration torque. Total required torque = load torque (constant torque) + accel/decel torque.

Here are some motor sizing forms on our website to help you calculate your inertia, torque, and speed requirements. Once you have these requirements, we can then confirm if the BMU460SA-50A-3 is the most ideal model to use.

-registration is required.

Here are some more information about the formulas used to determine motor requirements (and examples): ... lation.pdf

Since the BMU drivers offer momentary FWD and REV inputs, the limit switches won't work because once you start moving the motor, the limit switch would be off. It needs to be a constant on signal for the motor to keep running.

Re: BMU460SA-50A-3 Questions.

Posted: Thu Jun 12, 2014 7:40 am
by cstmwrks
Very good. Thanks for the answers. I've run load calculations and the BMU460SA-50A-3 will handle the load with a 1.5 safety factor. Not worried about a power failure causing the load to drop as the load is lifted through a worm gear drive. My only concern now is not being able to use a limit switch.

Re: BMU460SA-50A-3 Questions.

Posted: Thu Jun 12, 2014 12:18 pm
by om_tech_support_JT
You can use limit switches but you'll have to go through a relay and turn either FWD or REV input off when a limit is triggered. Yes a self-locking worm gear drive would be good at providing holding force.

Re: BMU460SA-50A-3 Questions.

Posted: Sun Jul 10, 2016 8:42 pm
by aldoned
My only concern now is not being able to use a limit switch.

Re: BMU460SA-50A-3 Questions.

Posted: Tue Jul 12, 2016 10:19 am
by om_tech_support_JT
Hi aldoned,

If you cannot use a home switch or limit switches, perhaps our AZ series stepper motors with absolute position feedback would work for you. You can set an absolute home position as well as software limits that prevent the motor from traveling outside a certain range.