Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: MarkR on May 22, 2006, 10:25:18 PM
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I am using a 3 axis driver board from HobbyCNC.com. I have set the jumpers on the board to 1/4 step microstepping.
I am confused by the 'steps per' setting in the Motor tuning setup. I am using 1.8 degree 200 step motors with 200 oz/in torque. I am using lead screws of 5 turns per inch for X and Y, and 16 tpi for the Z axis. I have the same motors on all 3 axis.
So, in order to set up the software properly, do I use the 2000 'steps per' setting? I have watched the video and read the manual, and am just a bit confused if I have done this properly. I set the value to 2000 'steps per' and I am calibrating in inches in the system.
(My initial thought is that I am set for 1/4 step micro stepping, so that would be 4 steps per turn, times 5 turns per inch, so it would be 20 steps per inch, but since that is SO far off from what I see in the manual, I am confused.)
Thanks for the help!
Mark
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Actually "steps per" means steps per unit, if you are calibrating in inches, then you need 5 complete motor turns (assuming direct dive), if you were not using microsteping this would translate into 200steps*5turns=1000 steps per inch, since you are using 4 microsteps per step, then that would yield 4000 steps per inch.
Same thing with the 16 tpi screw, 200*16*4=12800 steps per inch on that axis.
Hope that helps
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Thank You! That makes sense, and I will adjust my settings accordingly.
Whew! And I thought BASKET WEAVING was technical :)
Mark
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WOW! What a difference that makes in the cut speed! I KNEW something was wrong, as the speed was SO slow. Thanks again!
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Uh Oh! The last post was based on testing the settings in Mach 3 without connecting it to the driver board. When I do connect it, and run the axis with the arrow keys, I get a VERY erratic jumping of the motors and NO torque. So, I know I am over stepping them with this setting. I have tried the slowest settings on both vel and acc and had the same thing happen.
When I set the motors at '20' steps pe, I get slow travel and rock hard torque.
Setting at 2000 per gets similar jumpiness and loss of torque. My driver board micro stepping is set for 1/4 step.
Any ideas as to what is happening?
Thanks again!
mark
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Try running a gcode program, or an mdi line
something like:
F20 (or some other number you think you should be able to get it to run at)
G01 x10
and see how that behaves
Another thing might be the voltage you are running the board and motors at
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Move the sliders for the Accel and Max vel. That should get you up and running :)
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I spent quite a bit of time in the motor tuning section today, and what I see happening is this:
If I set my 'Steps per' to the 4000 setting (1/4 step setting on the driver board = 4 microsteps per step*200steps = 800 per turn*5 lead screw turns per inch = 4000 "Steps per'), then tough the sliders as instructed, I get jumpiness. I then move the sliders to lower settings and I get better movement, but much slower travel.
I am guessing I need more voltage (only 12 volt supply @ 60 amps for a 3 motor @ 3 volts each set up).
More tinkering to come, but I think you guys have given me the right direction. What I wish I knew was what speed I should be satisfied with using this set up...
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Take the voltage up to about 60V and I think it will help you with you rapids :)
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I'm not sure the hobycnc board will be able to take 60V, check with them.
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Okay 24 ;D
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For the record, the HobbyCNC board will take a max of 48 VDC ;D
I am curious, I have 2 12 VDC supplies, one with a 10 amp rating, and one with a 60 amp rating. If I were to put these in series to get 24 VDC, would that work (at least to run tests until I get the whopper transformer I am ordering)?
Thanks for the feedback!
Mark
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It will work but try not to go over the 10Amp... That would be Very bad for the power supply...
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I am just checking motor movement and have yet to get a cut made with the table. I will see what I am missing at 12 volts by trying it together. I don't think basic movement will over stress the motors to pull more than the 3 amps each that they are rated for.... Will it?
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Maybe.. Lower Voltage = Higher amps (Ohms LAw). I'd get a DC Current Meter and test it.
HTH
Sid
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***EDIT***
Just discovered my X axis lead screw motor coupler was loose... BIG problem if you want to get a motor to turn the lead screw....Friction fitting will only move the screww so much :( Maybe this is the source of my problems !! :-\
Hi Again:
I don't have enough hair left to be pulling it out. So, I again turn to the gurus of Mach to see if I am missing something.
I am getting almost zero torque today when testing at any setting. Do I need to shut the program down and re-start it when I make changes in the motor tuning section? I hit the sliders (per video instructions) and then reselect the axis and push the arrow keys.
What I am getting is jumpy motors. I believe I have set the speeds up properly (500 rpm to start = 100 inches @ 5 tpi) and the acceleration is around mid way on the sliders.
I am running at 12 volts, so I am not really sure the speed I should see at max velocity. So, I am going to spend forever trying to get this set up to work, but atleast I see movement!
I ran my first cut last night and the dropped steps left my X axis about 1/2" short of the place it should have stopped. Y seemed fine.
Sorry if this just seems like repetitive questions on the same problem, but I am stumped, and I used to think I was pretty good with thinking this stuff through.
Perhaps it is my laptop? I tried to get it set per the optimized recommendations, and STILL had the same graph profile as before I did anything! BIG spikes and lots of them. Using a Dell Laptop with 1.5 GHz processor and 1 gig of RAM. My desktop has a great graph profile when testing and I am thinking of trying this one to see if that matters....
Thanks for helping me think this one out!
Mark
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Hey Mark,
Not sure if this is any help to you but perhaps it might stimulate your hair folicles to grow back...
Like you, I am runing a 12V Stepper system. When I first installed it, I tried to get get max resolution min 2000 steps per unit which would equal a cutting accuracy of .001"-kinda the industry standard. I got things to work that way but, like you it was either exscruciatingly slow moving with buttloads of torque or zippy speedy with almost no torque and would mis steps if you blew air in the general vicinity of the machine.
I spoke with the dude who made the driver board and he said "more voltage" will solve the problem. Well, after having purchased the 12v supply, installed it in an enclosure that was already on the verge of being too small, combined with the additional cost of getting a larger pwr supply, I thought... Do I REALLY need .001 resolution?
In my case, I decided that I did not. So, I changed out a couple of pulleys to give me more speed and settled on a resolution of .01 for the time being.
I suppose that for most people this low of a resolution is insuffiecient but for me cutting wood and foam, it works great. I have better than 1/64" accuracy which, when cutting wood is a splinter so small I doubt most people would even notice the diff.
The machine immediately started runing faster (around 200 ipm) with torque to spare.
Food for thought- Good Luck!
Regards,
Sid
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I think running your steppers at 500rpm, with 12 or 24 volts, might be pushing it a little, I could be wrong.
Most laptop paralel ports output 3 volts, instead of the usually needed 5 volts, try your desktop, unless you have a breakout board that takes care of that voltage difference.
You dont have to restart Mach everytime you tune the motors, but you do need to save the axis settings with each modification for it to work.
You could try out Sids suggestion, steppers have the most torque at low speeds, so if you add a 1:2 pulley system (1 turn of the motor=2 of the leadscrew, not the other way around) it just might have enough torque to run your cuts without loosing steps, and increase the speed in the process. You could check the torque speed curve of your steppers to see what would happen to the available torque and speed with the 3 scenarios (1:1, 2:1, 1:2 ratios).
Dont give up, have patience.
Regards
Fernando
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Hey Guys!
Thanks for the encouragement! I will look at modifying the machine with the pully system. Great idea.
After posting, I hit my x carrage and it moves on it's own, making me look underneath and seeing the motor connector was loose and not even connected to the motor. This was causing the 'slipping' to the extent it was. I re-attached the lead screw, and now at least I have movement. What I was initially thinking was a stalled motor, was an un-attached motor (Good grief!).
BUT, I am having some erratic motor speeds (the lead screw does not turn very smoothly, but in rapid jumps of turns). It is rapid enough to get a decent linear motion, but not the silky smooth operation I had thought I would see.
Most of my requirements will not require .001 accuracy, so your suggestion to make a ration reduction unit is well taken. I too and just cutting wood and foam, so it is not like I am doing the kind of machining the big boys here are doing.
Thanks again for the encouragement! :)
Mark
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BTW, I DID find that using 500 RPM was way too fast. I dropped the velocity to 40 ipm and saw a decent torque to speed, so I left it there.
I actually cut my first part and now am trying to learn how to compensate for the tool diameter.
THAT is a subject for a new thread in the Lazy CAM area :)