Or take any 8 wire motor, and the unipolar torque will be 70% of the bipolar torque.
Or take any 8 wire motor, and the unipolar torque will be 70% of the bipolar torque.
Gerry
UCCNC 2017 Screenset
http://www.thecncwoodworker.com/2017.html
Mach3 2010 Screenset
http://www.thecncwoodworker.com/2010.html
JointCAM - CNC Dovetails & Box Joints
http://www.g-forcecnc.com/jointcam.html
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Interesting, I never really liked the stall Torque ratings of steppermotors.
Dose not really tell you anything important nobody runs there machine
when its stalled.
Torque * speed = work
How dose Bipolar compare to unipolar concerning useable speed?
Seams the cheaper unipolar drivers allow for more amps and volts
dose this offset the cost for a little bigger motors to make up the
30-40% loss of a unipolar driver?
Is there a best bang for your buck?
Ok, I've done some research on Unipolar versus Bipolar motors:
Step motor reference
UNIPOLAR
The drawback to using a unipolar drive however, is it's limited capability to energize all the windings at any one time. As a result, the number of amp turns (torque) is reduced by nearly 40% compared to other driver technologies. Unipolar drivers are good for applications that operate at relatively low step rates.From ST MicroBIPOLAR CHOPPER
Bipolar chopper drivers are by far the most widely used drivers for industrial applications. Although they are typically more expensive to design, they offer high performance and high efficiency. Bipolar chopper drivers use an extra set of switching transistors to eliminate the need for two power sources. Additionally, these drivers use a four transistor bridge with recirculating diodes and a sense resistor that maintains a feedback voltage proportional to the motor current. Motor windings, using a bipolar chopper driver, are energized to the full supply level by turning on one set (top and bottom) of the switching transistors. The sense resistor monitors the linear rise in current until the required level is reached. At this point the top switch opens and the current in the motor coil is maintained via the bottom switch and the diode. Current "decay" (lose over time) occurs until a preset position is reached and the process starts over. This "chopping" effect of the supply is what maintains the correct current voltage to the motor at all times.
Now, if the torque is reduced, and it says it's better for "relatively low step rates" can anyone tell me how slow is slow for the Unipolar case?BIPOLAR PRODUCES MORE TORQUE
The torque of the stepper motor is proportional to the magnetic field intensity of the stator windings. It may be increased only by adding more windings or by increasing the current.
A natural limit against any current increase is the danger of saturating the iron core. Though this is of minimal importance. Much more important is the maximum temperature rise of the motor, due to the power loss in the stator windings. This shows one advantage of the bipolar circuit, which, compared to unipolar systems, has only half of the copper resistance because of the double cross section of the wire. The winding current may be increased by the factor Ö2 and this produces a direct proportional affect on the torque. At their power loss limit bipolar motors thus deliver about 40 % more torque than unipolar motors built on the same frame.
If a higher torque is not required, one may either reduce the motor size or the power loss.
Guys I come from the RC airplane world and most recently building my own brushless motor from CDROM parts. The biggest obstacle in "jumping in" to CNC in is knowing what is good enough. I want to start with adding CNC to my Taig lathe to get a feel for things, but I don't wnt a "lot" investment in equipment. The one video of the application of HobbyCNC's drive was not as impressive as I would have liked, though I don't know what ipm the guy used. Any other videos of this system in service with reasonable speeds to showcase the possibilities?
CNCadmin, can you explain why you picked this kit ... ie the decision process.
Jay
The reason I picked this drive is for the following reasons-
- This seams to be a popular chose for a low cost drive
- for my application, a most expensive drive was not necessary (bipolar drive would have been nice)
- I wanted to give it a try, I like to see things for myself
- the biggest reason I need 1/16 micro stepping for my application, do to the fact I'm running a complete belt system
I did my test on the board to verify that the components that I installed were done so correctly. The test failed, I did not get 5volts on the test point, so after close inspection, (using a magnifying glass) I found a bridge in one of the from soldering. Once that was cleaned up, a re-test gave me the green light to install the rest of the parts. Now on to testing the out put to the steppers. So far I have spent 1/2 hour on building the board, I waiting on my case and transformer to arrive. Stay tunned...
JayC
There is nothing wrong with unipolar steppers. Yes a bipolar of the same arrangement is stronger, but if you don't need it, it's not an issue. Unipolar electronics are almost aways going to be less expensive. I think the biggest thing that should concern you is what can you get for what price. If brand X bipolar driver costs $50 more than brand H's unipolar, and you can get a unipolar motor(s) that have the strength you need, it probably is the way to go. Stepper performance is really a combination of the driver, motor (and type) and power supply. By that I mean if you have a 6V rated stepper, and you run it bipolar with a chopped biploar driver and a 12V power supply, you may (probably) not be as happy with the result as the same motor being run with a chopped unipolar driver and a 44V power supply.
Phil
BTW, I would add brand H driver is a pretty good bang for the buck if you can solder. Plus I imagine if at a later date you wanted to drive your motor bipolar, you could sell your brand H board without any difficulty.
Phil, Still too many interests, too many projects, and not enough time!!!!!!!!
Vist my websites - http://pminmo.com & http://millpcbs.com
We get 2,000RPM no load on our 127 or 200oz-in steppers at 40VDC with our 4AUPC driver board. FASTER than the Xylotec board we tested against.Originally Posted by Jay C
Dave Rigotti
HobbyCNC
Jay C,
You can't make a determination on somebody elses video, to many variables. Start by picking your motor.
Dave,
"We get 2,000RPM no load on our 127 or 200oz-in steppers at 40VDC with our 4AUPC driver board. FASTER than the Xylotec board we tested against."
Now that's misleading!
Phil
Phil, Still too many interests, too many projects, and not enough time!!!!!!!!
Vist my websites - http://pminmo.com & http://millpcbs.com
Well, for the lead screw since I'm adding one, I am eyeing the 127 oz-in one from Hobbycnc for the carriage. For rhe cross slide I need to think more about what will fit Also, when I said I didn't want to invest too much I meant I didn't want to buy twice ... I don't mind buying the best solution for me onceOriginally Posted by pminmo
The videos were so I could see the potential.
Just an update. I ordered a driver board and a 80 oz-in stepper from Dave for my lathe project. After reading the allegromicro datasheet on the driver chip, looking at the photos on Dave's site, and reading some feedback on this site I concluded that this was the system for my needs. I expect the kit to arrive today or tomorrow and I have volunteered to write a tutorial (with lots of pictures, tips and tricks, a description of how the circuit works and what section does what, and a troublshooting section/FAQ to ease any electronics learning curve.
Thanks, and Paul would you prefer that I start my own review thread or tack on here to yours?
Jay
The more reviews the the better, I be comparing this board to the Xylotec board as well. I just have not had any time to devote to this right now hopefully next week I will get back to this. But please be my guest, start a new thread.
I was really impressed with the Hobby cnc three axis board. When I ran a variety of tests using a 28VDC power supply it ran quite nicely with no lost steps and there was no stepper motor resonance. However, when I installed the unit in one of my nice cases with 36VDC power supply and ran the same tests I was surprised to run into stepper motor resonace using the G03x0y0i.4f3 G code command with turbocnc and also with desknc for dos.
I suspect that the 8 volt difference is the problem even though I have a 10000 UF 63 v cap in the power supply. I have a feeling that the problem is caused by the common ground plane and the higher voltage.
Is anyone else running their hobbycnc boards at 36VDC and set for 3A and experiencing what appears as stepper motor resonance even though it is set for 8 microsteps?
Dan
Dan,Originally Posted by Dan Mauch
We ran many test cycles at 42VDC with 3 and 4 3A steppers hooked up. No problems detected on this end. Try turning down the Vref to 70% of the actual value. We find the steppers stay MUCH cooler and the loss of power (RPM) is hardly noticeable.
Dave Rigotti