[tdperk]

Hello all,

This is not the first post I wanted to make. I caught ebay fever and bid on what turns out to be a servo motor, Cleveland Motion Control model BMR4445ACGBOHS0002. It was described as a stepper, but I can now see from the documentation that it is not intended to be a stepper, but a servo only.

Does anyone have experience with these, such that you could tell me if I can modify it to be a stepper, or should I put it in a closet until I can use a dedicated servo motor?

Thank you, Tom Perkins

[ger21]

Just sell it again. You might even get more than you paid. No, you can't turn a servo into a stepper.

[H500]

Is there any reason why you can't make use of a servo motor? With the proper driver, it can do anything that a stepper can and will even be faster.

[tdperk]

Hello H500,

All my research and circuits experimentation has dealt with steppers, also, it is not merely not the "stepper" motor that it was described to be in the listing, it is also very much more than I need.

It isn't 200oz/in max, it's 200lb/in max, roughly 2.5kW. It has a 350VDC max back emf at 7krpm. I can use stepped up and rectified house AC current to supply it at about 1/4 of it's rating easily enough, and that's all I need--and if it were in fact a stepper, I'd feel fine with designing and building a drive for it, but I just don't know servos.

What sites would you recommend to help me homebrew a driver for this beast? I've looked at the UHU site: http://www.uhu-servo.de/ I don't have any kind of feel for servos though.

Thanks, Tom Perkins

[Bob Cole]

Tom:

If the motor you received was NOT what was advertised, I would contact the seller IMMEDIATELY, and ask for a FULL refund. HE (the seller) has a responsibility to sell exactly what he listed. If you did NOT receive what you bid on, you have a legitimate claim for refund. EBay will assist you if you do not get satisfaction from the seller.

Bob C.

[tdperk]

Hello Bob,

I have contacted them, but I just won it today at around noon. I realized the item was not a "stepper" about a half hour after I bid, and to be fair it was also described as a servo, the discrepancy could have clued me. I don't have a response from them yet, but it is early.

I would have appreciated them not using the world stepper in a description of a servomotor though.

Yours, TDP

[Bob Cole]

Tom:
If you just won the bid, perhaps by contacting EBay right away :stickpoke (like NOW). you may be able to withdraw your bid.
Bob C.

[tdperk]

Hello Bob,

I've already contacted the seller and eBay, I am hoping for a positive reply. Alternatively, I'll relist it--with a more accurate description and with some electrical tests performed--and hopefully move it at a small profit (the most I deserve) or at worst a small loss (I hope that's the worst I deserve).

Yours, TDP

[H500]

The high power and voltage makes it a poor candidate for a home-brewed controller unless you really know what you're doing.

Most home cnc machines only need 50-200 watts of power. A stepper would be much simpler. Take a look at www.automationdirect.com. A decent motor can be bought for $30-40.

[Bloy2004]

I didn't notice if you listed the actual auction... could you provide that so I could view the "ended" auction?

[Al_The_Man]

It isn't 200oz/in max, it's 200lb/in max, roughly 2.5kW. It has a 350VDC max back emf at 7krpm.

Are you sure that is the right sizing, I would have expected a larger motor for that power, going by the dimensions shown.
Al.

[tdperk]

It item number 7575629217

or URL

http://cgi.ebay.com/ws/eBayISAPI.dll...3D50%26fvi%3D1

Here's the URL for the motor sales brochure.

http://www.cmccontrols.com/downloads...duct_Guide.pdf

Yours, Tom Perkins

[H500]

Looking at the torque curve, the continuous rating at 5000rpm is closer to 170w, assuming my math is correct.

[tdperk]

The 4045 model rating is 2440W.

Haven't heard from Ebay or the seller yet...

Thanks, TDP

[H500]

Not according to the torque curve. 2440 is likely a peak rating that cannot be maintained for for than a few seconds without burning up the motor.

[unterhaus]

Power = 2500 watts = 5.1 N*M * RPM * 2 * pi/60 = RPM/2 (close enough)
RPM must be 5000
Looks like the motor will go 10k rpm at 350 volts.

Although my reading of the power rating is rated volts * continuous amps

It's going to be tough to buy a control for that motor, and making one is not going to happen. Watch Ebay for a brushless controller that will work is all I can suggest.

[H500]

You're correct. I'm so use to values in oz-in instead of lb-in that I automatically divided by 16 in my calcs.

There are several people trying to design a brushless motor controller. I believe rutex has a controller in the $200 range but it won't reach anywhere near 2500w.