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wildbill
23-02-2010, 10:16 PM
I recently got some bipolars from a forum member, they are 23HS8404's by Motion King, in the spec sheet on their website, there is no listing for the voltage of these motors, can anyone help with this ?

Wildbill

irving2008
24-02-2010, 01:36 AM
thats because the voltage of the motor is fairly irrelevant for a bipolar motor. Its the current that matters and assuming you have a constant current driver (e.g. either a chopper or PWM) that is the key value. The other key parameter is inductance of the windings as this tells you how the motor torque will roll off at speed and therefore the ideal driver voltage, which is 32 x sqrt(inductance in mH). so a 3mH motor ideally would like a 32 * 1.732 = 55v driver. Of course a lower voltage will work but wont get the same torque at the higher speeds.

If you want to know more just ask...

Swarfing
24-02-2010, 01:37 AM
Bill

23HS8404 Double stack, 76mm, 6mm, 1.8, 40vdc/4.2amp/2 phase, 180N.cm

Swarfing
24-02-2010, 01:38 AM
Irv you clicked [enter] at the same time

irving2008
24-02-2010, 01:46 AM
Thats the breakdown voltage of the windings, not the operating voltage. A more useful spec is http://www.alibaba.com/product-gs/281685069/23HS_stepping_motor_Size_57mm_1.html which shows these are 4.2A 0.6ohm motors (nominal coil volts 2.52v) and 1.8mH so ideal driver is 42v, they should work good on a 36v driver.

Swarfing
24-02-2010, 01:53 AM
the is what was on http://www.rhonmac-cnc.co.uk/electronic_hardware.htm. shame they never explain?

wildbill
24-02-2010, 01:59 AM
Thanks for that, the motors are double stack, 76mm long and are (i think) based on nema23's the motion king website states that the current rating is 4.2 amps, i dont know if thats per winding (per phase ?). Can you recommend suitable drivers for these ? I have already started building the table and gantry with bearings made from alli angle and skatebord bearings, i would like to get these motors turning and download some software, just to get thing moving along (no pun intended). lots to think about. Thanks for your help.

Wildbill.

wildbill
24-02-2010, 02:06 AM
While im on, derlin nuts ? ballscrews ? backlash? , it would be very helpful if there were a place on the forum for a glossary of terms and explanations of what these and other related thing were, to help newbs like myself. I know there is loads of info here, but that would be great if it was all in one place.

irving2008
24-02-2010, 10:09 AM
Well a good starting point might be the tutorial I wrote here (http://www.mycncuk.com/forums/showthread.php?1524-What-size-stepper-motor-do-I-need-A-tutorial)on choosing stepper motors...

A glossary is a good idea... let me think on it... but for a simple explanation:

most CNC machines use some form of screw mechanism to convert rotary motors to linear motion. The motor turns the screw and a nut riding on the screw transfers the power to the linearly moving part. Screws are generally made of carbon steel. To maximise power transmission they have special thread forms, usually trapezoidal or square (Acme). Minimising friction is critical, so the nuts are made of bronze or of hard but machinable engineering plastics like delrin. Typically the energy transmission of such an arrangement is 30% because of the frictional losses. Nuts are not perfect, if there was a 100% fit the friction would be very high, so there is a point where the screw turns but the slop between the thread of the screw and that in the nut means the nut doesnt move.. it is tiny but measurable. This is backlash and its one of the high goals of engineering to minimise it but still make the screw turn freely. Ballscrews use a different thread form and the nut comprises a number of ball bearings that run round the screw thread and recirculte back through a tube. Because the balls rotate and therefore have low friction they can be a much closer/tighter fit than a conventional nut, meaning reduced backlash (not zero as some claim) and higher efficiency (80%). Ballscrews are the screw of choice but the cost is 20 - 50x a standard screw.

irving2008
24-02-2010, 10:37 AM
Thanks for that, the motors are double stack, 76mm long and are (i think) based on nema23's the motion king website states that the current rating is 4.2 amps, i dont know if thats per winding (per phase ?). Can you recommend suitable drivers for these ? I have already started building the table and gantry with bearings made from alli angle and skatebord bearings, i would like to get these motors turning and download some software, just to get thing moving along (no pun intended). lots to think about. Thanks for your help.

Wildbill.These are bipolar 4 wire motors. the rating is per phase. Ideally you'd want drivers capable of 4.2A/phase, 36V to drive these, such as Zapp's PM542 (http://www.slidesandballscrews.com/pm542-microstepping-driver-p-111.html?cPath=44). For three axis you'd need a 10A power supply, such as this one (http://cgi.ebay.co.uk/NEW-36V-Power-Supply-for-CNC-Servo-Stepper-Motor-Driver_W0QQitemZ170437625521)on ebay.

wildbill
24-02-2010, 12:23 PM
Thanks for that to all that responded. So, would i be correct to think that the backlash is the slack between the nut and the threaded bar ?. I think i got an idea (to quote Michael Caine) on how to work around this problem with low cost studding !!! i'll work on it and update asap. Thanks again to all, this is just the info a newb requires.

Wildbill.