[acondit]

in-oz = 8 * Lbs / (pi * TPI)
in-oz = 8 * 50Lbs / (3.14 * 5 TPI) = 25.5 in-oz needed

Watts = in-oz * RPM / 1351
Watts = 25.5 in-oz * 1,200 RPM /1351 = 22.6 Watts of mechanical power from motor.

Easy! (use a 2A to 3A per phase motor @ 24VDC to 36VDC supply).

Mariss

Ok, Mariss, where does the 8 come from?

Alan

[Mariss Freimanis]

Ehm,..

The equation for leadscrew thrust in Lbs is:

Lbs = (pi * TPI * in-oz) / 8

I derived the equation quite a while ago (2 years?) and it would hurt my head to do it again. May I demure and ask you to take it on faith it is correct? It is throughly tested and I believe it to be accurate. I'll go through the process again if you insist but I will probably hate you until the incurred headache goes away.:-)

Mariss

[High Seas]

http://pdf.directindustry.com/pdf/li...36373-_15.html

page 15 assuming 100percent efficency for max torque i guess.

sorry-on screen kbd sux cheers--jim

[Mariss Freimanis]

OK, good point. Include efficiency (0 < e < 1) in the numerator. Figure e = 0.15 for the crappiest Acme thread, e = 0.95 for a good ball-screw. Re-write the equation as:

Lbs of thrust = (pi * TPI * in-oz * e) / 8

Mariss

[acondit]

Ehm,..

The equation for leadscrew thrust in Lbs is:

Lbs = (pi * TPI * in-oz) / 8

I derived the equation quite a while ago (2 years?) and it would hurt my head to do it again. May I demure and ask you to take it on faith it is correct? It is throughly tested and I believe it to be accurate. I'll go through the process again if you insist but I will probably hate you until the incurred headache goes away.:-)

Mariss

OK, I thought maybe it was some easy constant that I was missing? Most of the time in your formulas I am ultimately able to figure out where they derive from.

Thanks,
Alan

[ger21]

I use this one.

Force (ounces) = ((2 x pi x torque)/ lead) x screw efficiency.

Or, I go to Nook's website, look in their catalog for the screw you're using (either acme or ballscrews), and they tell you the torque needed to lift 1 lb.

[sawmiller]

Steve,

The G250 will run any 3.5A motor just fine, but if the inductance is high enough it will take a higher and higher voltage to "push" the current through the windings. You can run a 10mH motor, but it will have miserable torque at 50V. Of course, the easy way around this is to buy a motor that has a lower L rating, but the world will not end if you run it at less than optimal voltage. What you will see is a low amount of torque for how many amps you are feeding it.


Marcus Freimanis

so to be specific.... i have some keling 425 oz-in motors, inductance in bipolar paraell is 6.8 mH according to the sheet.
i was looking at these drives as replacements for my pminmo drive boards.
but due to mH these will be worse ?


unfourtunately this is just a hobby for me, i really cant afford to dedicate
4 x $147 (203V's) to a hobby, however 4 x $31 and reusing the pminmo breakout board is affordable.

dan

[Crevice Reamer]

so to be specific.... i have some keling 425 oz-in motors, inductance in bipolar paraell is 6.8 mH according to the sheet.
i was looking at these drives as replacements for my pminmo drive boards.
but due to mH these will be worse ?


unfourtunately this is just a hobby for me, i really cant afford to dedicate
4 x $147 (203V's) to a hobby, however 4 x $31 and reusing the pminmo breakout board is affordable.

dan

The 425s would be happy running with up to 83 volts. They will RUN at 48 volts, with the mighty mites, but will not be as powerful at higher rpm. You COULD drop down to the 282 oz motors, and use the min gs though. They would SCREAM at 48 volts. In this case, you would actually get more power at high rpm from the smaller motors.

CR.

[acondit]

I use this one.

Force (ounces) = ((2 x pi x torque)/ lead) x screw efficiency.

Or, I go to Nook's website, look in their catalog for the screw you're using (either acme or ballscrews), and they tell you the torque needed to lift 1 lb.

Ger,

Thanks, I thought it might be related to the lbs - oz. relation. So now it is clear that it is the result of dividing both sides of the equation by 16, which result in the conversion of ozs to lbs on the left hand side and the subsequent factoring of the 2 out of the top and bottom of the right hand side.

Alan

[kiwibum]

The 425s would be happy running with up to 83 volts. They will RUN at 48 volts, with the mighty mites, but will not be as powerful at higher rpm. You COULD drop down to the 282 oz motors, and use the min gs though. They would SCREAM at 48 volts. In this case, you would actually get more power at high rpm from the smaller motors.

CR.

Which is what I was trying to get at in earlier post. There is a limit to the size of the motor where you will get maximum performance/torque out of it with this driver. Above this limit the stepper will still perform well but not to it's full capacity that it could perform with the next size up driver. As motors go up in torque ratings, the inductance goes up for 3.5Amps, if you get one with lower inductance it will require more current. e.g. from Lin Engineering spec sheet for:
294oz-in steppers:
- 3.27A, 5.2mH
- 4.2A, 1.8mH
434oz-in steppers:
- 3.15A, 6.1mH
- 6.3A, 1.5mH
861oz-in steppers:
- 3.15A, 8.3mH
- 6.3A, 2.1mH
The 294oz-in appears to be more close to optimum. This is normal, next sized up driver will have the same sort of limits, as will all other drivers. The important thing to understand is expecting that you will get the maximum performance with the G250 out of your 3.15A 861oz-in stepper because the driver is capable of 3.5A (as I was expecting till I started looking into the specs more) is not correct. You are better off getting the G201 which will get full performance for it. You will still get good performance out of them but there will be a sweet spot where a lower torque motor e.g. 294oz-in will be better than a 861oz-in one (or maybe it's bigger I don't know the exact size) and will be noticeable enough to say the extra paid for the 861oz-in one wasn't worth it or I should have spent the extra and got the G201's. Now although I have a automation engineering degree and back ground in electronics/technology this stuff is new to me so I could be completely out of the ball park here and very happy to be corrected (please do so). The torque ratings are examples to explain a point, I don't know what the sweet spot sized motor would be compared to a larger one.
Thanks Steve

[Crevice Reamer]

Well, basically you want to size the motor with your power supply voltage. Try to use the maximum usable voltage for best power out of that motor. The PSV must be <= to the top voltage limit of the drive. You will also want to wire in Bipolar Parallel for best power at highest rpm. The formula Mariss gave for highest usable motor voltage is 32 times the Sq root of the inductance.

If that result for your motor is higher than the G251s top of 50 volts, but lower than the g201/203 limit of 80 volts, then for best performance you may need to go to the more expensive drives.

It would be cheaper though to buy new, more compatible motors to use with the G251s. A whole set of three smaller motors would still cost less than only ONE G203v.

CR.

[ger21]

Keep in mind that most people are running those motors with Xylotex and or HobbyCNC drives. These new Gecko's will give double the performance of a Xylotex, and a little better than a Hobby CNC. Without resonance issues, too.

[wolfdagon]

I don't know the inductance of the motors that I have, which are from HP Laserjet III printers. So how can I determine the highest useable motor voltage without knowing his value? I will probably upgrade to larger motors once I get my machine built and running. But I already have these motors and want to see how well they work with my machine before making any changes.

[Crevice Reamer]

I don't know the inductance of the motors that I have, which are from HP Laserjet III printers. So how can I determine the highest useable motor voltage without knowing his value? I will probably upgrade to larger motors once I get my machine built and running. But I already have these motors and want to see how well they work with my machine before making any changes.

Does it have only 4 wires? Four wire motors are bipolar motors and these have relatively low inductance. If you know the motors rated voltage, you are probably safe to use 20 times that. If you don't know the voltage, but have the resistance and amperage per phase--multiplying these together will give you the voltage rating.

For example, motor is stamped 2 volts. 20 x 2 = 40 volts should be okay.

CR.

[sawmiller]

thought about it all day,
and am going to buy the mini -g's to run with the 425 oz-in
am currently running 36 volts power supply, so i will gain 10 volts, and thats got to help. also i would like the motors to run cooler....
if i'm not happy with the preformance, i can always buy some 282's as reamer suggested and sell the 425's
dan
now to look at the breakout board schematic on the other page.......

[Crevice Reamer]

Sounds like a plan.

...am currently running 36 volts power supply, so i will gain 10 volts, and thats got to help. also i would like the motors to run cooler....

I don't understand. Did I miss something? How are you gaining 10 volts?

CR.

[High Seas]

These new drives will create a whole new range of possibilities for motors and power supplies. (Just as Mariss envisioned).

As a user - I'd really appreciate a matrix/spreadsheet outlining some motor/power supply combinations/options that make sense.

As a consumer - I would like choose a reasonable combination.

If such a matrix/spreadsheet were coded to show the sweat spot - I could choose accurately and invest wisely.

The number of motors is reasonably finite - and there are a host of "most popular brands." The not so trivial step--would be the combinations and including serial vs parallel on a given motor - but could be accomplished by some of the really clever people on the CNCZone. (Sorry I'm not one of those - I'd jump in.)

Something to do in anticipation of their availability?

:cheers: Jim

[sawmiller]

Sounds like a plan.



I don't understand. Did I miss something? How are you gaining 10 volts?

CR.

my current driver max volts is 38, mini- g is 50 max... so i should be able to wire a bigger power supply and get more volts to the motors
dan

[Crevice Reamer]

Oh! That's a GOOD idea. Maybe one like the KL-350-48. That would gain you 12 volts.

http://kelinginc.net/SwitchingPowerSupply.html

CR.

[the4thseal]

i looking for motors for this drive.....looking for the best performance and would like allof your input. i am going to get the four axes unit. lets hear it.