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

Gear boxes on servo motors should not be the first resort nor the second
resort for random XY positioning.

Gearboxes are best implemented where a pattern of operation is well
known and the issues associated with backlash can be dealt with. One
example would be secronizing conveyors or tohter apparatus that has a
tendency to move in one direction. The other possible consideration
is when you need to develope a large amount of torque in a small place.

If you don't have a motor that allows direct drive, the next best thing
to implement is a belt drive if the ratios can be kept reasonable. If
this can't be done then you need to either look at motor selection or
servo lopp setup.

Thanks
dave



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...
>
>Here are my choices:
>
>1)
>160 RPM Dunkermotoren, #88442/88851. This is a high quality German
>made gearmotor with opitcal encoder. The input voltage is rated at
>24 VDC @ 2.7 amp. The gearbox ratio is 20.25:1 Tested on 24 VDC the
>no load speed is 178 rpm @ 0.6 amp. With a 100 oz in lad the rpm is
>173 with a current input of 1.1 amp. We estimated that the motor rpm
>with a 300 oz in load will be approx. 160 rpm @ 2.7 amp. The motor
>and gearbox have ball bearings. Shaft: 12mm dia X 7/8" long. The
>shaft has a 3mm cross-drilled hole located approx. 5/16" from the
>shaft end. The encoder is Hewlett Packard modular device (series
>9100) with an output of 500 counts per revolution. The encoder
>produces TTL compatible quadrature outputs. Encoder input voltage is
>5 VDC @ 40 mA max. The motor has 6" long flexible lead wires. The
>front of the motor gearbox has a removable mounting plate that has
>four tapped mounting holes. The tapped holes are 4mm X 0.7mm pitch.
>Dimensions: 2 1/2" dia. (max) X 7 3/16" long (excluding shaft but
>including encoder). Stock #DCGME2201 $59.95
>
>
>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. Motor current will be approx. 4 amps. The motor rotation can be
>reversed by swapping the leads connecting the motor to the drive
>electronics. As shipped the motor rotates CCW. The drive motor is
>permanent magnet type rated 24 VDC, and has ball bearings. The
>gearbox has sleeve bearings. Shaft: 8mm dia. x 1-3/4" long. Motor
>shaft has a cross-drilled hole with pin plus a plastic cog pulley.
>The pulley is approx. 1/8" or 3mm pitch with 20 teeth. This pulley
>is easily removed. Dimensions: motor 2-3/8" sq. x 6" long (excluding
>shaft). Drive electronics board 3-3/16" wide x 2-5/8" deep x 1-5/8"
>high. Stock #DCGME9650 $47.50
>
>
>Number 1) may require a pulse multiplier due to 500cpr encoder and
>~29to1 gear ratio. I think the 500cpr will be for the motor shaft
>and not the output shaft (I think).
>
>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.
>
>This is from candhsales.com. They also have shaft couplers
>(spider type) for 2.95 or 10 at 2.50 each. These have 1/4 shaft
>and set screw. I will probably pick up a few.
>
>Thanks,
>
>Eric
>
>
>
>
>
>
>
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