Re: [CAD_CAM_EDM_DRO] Re: mill servo conversion ?'s

carlos_is_dead wrote:

>some last questions and summations to make sure I've got this all
>together:
>
>Using Camtronics motors as an example, they state their motors are 38V
>at 900RPM.
>
>That means Kv = 38v / 0.9 KRPM = 42.2V/Krpm
>Kt = Kv * 1.35 = 57in oz/amp
>You state the terminal resistance (Rt) is high at 4ohm, and on the 36V
>power supply inclued in the kit, maximum torque occurs at stall with 9
>amps supplied. 9 A * 57 inoz/A = 513 in oz total.
>Because of the back emf, torque will decrease at a rate of
>Kv / Rt * Kt for every 1000 RPMs or 42.2V/Krpm / 4ohm * 57inoz = 601
>in oz for every 1000RPMs (coincidence?)
>
>Maximum torque can be achieved over a wider range of speeds by simply
>using a higher voltage power supply, and limiting the amount of amps
>supplied to the motor through the gecko drive through adjustment of
>the pot in order to avoid damaging the motors.
>
>Finally, you stated that the motors in this auction:
>
>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=26261&item=3831771088&rd=1&ssPageName=WDVW
>
>are the same ones as camtronics sells. However, it lists the terminal
>resistance as 2.6ohm which I assume is what you're referring to when
>you say camtronics' motors are 4-5 ohm.
>

Well, it looks like these motors have a slightly different winding
configuration in
them! I should have looked closer. They also give 44 Oz-In/amp and
32.5 V/KRPM.
These figures actually are better for the intended use than the
camtronics motors.

> Does that mean these motors
>will run closer to peak torque on a lower voltage power supply? Follow
>my math here if you will. 2.6 ohm motors with a kt of 44ozin/amp and a
>peak torque of 600inoz means max stall amps are ~13.5amps, which means
>in order to see that torque, one needs a 13.5*2.6=35V power supply.
>
>

Yes, but that's at stall, only. You STILL need more voltage to get good
torque
at speed.

>I guess, restated another way: it seems these motors are better suited
>for the power supply camtronics supplies.
>
>How does one determine the capabilities of a power supply? They have
>continuous current supplied and peak current. How long can peak
>current be supplied? Is there any set relationship, or is it just a
>function of the type of components used? What value is normally given
>with a power supply; peak current or continuous?
>
>
>

You have to ask the maker. The continuous is the normal rating point, most
bulk supplies can deliver 2 x continuous power for a couple seconds every
minute. Without the manufacturer's help, you can't go much beyond these
very rough guesses.

Jon