Re: [CAD_CAM_EDM_DRO] re-selection of motors....avoiding another rathole

etauch wrote:

>Greetings,
>
>Recently I posted on the overheating servo drive issue. I have
>decided that instead of moving to belt and pulley, I would try
>a "gearhead" servo motor in the 160-500 rpm range. This is
>for running direct drive thru helical beam shaft couplers. I will
>calculate the exact RPM I need based on my leadsrews (10:1) I believe
>and desired IPM and pulse rate of my current PC.
>
>As this is my second attempt (current setup caused motors to
>get hot due to running of servos at low speed constantly), I am
>hoping to get some feedback on my motor selection.
>
>I dont forsee any problems, but does anyone have any input or
>comments. Thanks in advance...
>
>

Do these motors have zero-backlash gearboxes? I suspect they are NOT
zero-backlash, and the encoders are on the motors, so the machine position
will be inaccurate by the amount of the backlash. Don't assume because
there is an encoder on the motor that it is good for a precision positioning
application.

>Here are my choices:
>
>1)
>160 RPM Dunkermotoren,
>

160 RPM sounds awfully slow. With a 5 TPI screw, you will get 32 IPM.

>2)
>210 to 550 RPM JAPAN SERVO CO. MOTOR #DME60, GEARBOX #6H9F-H46. 24
>VDC gearhead motor with encoder and drive electronics. Gear ratio
>9:1 Encoder: Hewlett Packard HEDS-5600 with 100 counts output per
>revolution. As shipped the motor/encoder/electronics will give a
>variable speed between 210 and 550 rpm. Speed is set via on-board
>trimpot. As shipped the motor is set for 380 rpm. A 24 VDC input, no
>load current is 280 mA. At a 6 in-lb load the motor rpm will be 380
>rpm.
>

Is this the limit? Your #1 motor does 18.75 In-Lb, but 6 in-Lb sounds WAY
anemic. I can remember pushing 150 In-Lb, at least, on the handles of my
Bridgeport.

>Choice 2) looks good, but from the description they talk about
>reversing the motor leads to reverse the direction...not sure why.
>I would think all these motors would be "reversible". I am leaning
>towards this choice as I think I can get away with NO pulse
>multiplier here.
>
>

That's because the included electronics are one-way only. The motors
themselves are reversible.

Well, how many times are you going to ignore the identical advice
from people who've done it before, who tell you that practically all
the manufacturers, as well as most home-builders, use toothed belts?

Jon