I some sort of interested in crunching some numbers to see what I got here.
I checked my with a thread gauge and it has a pitch of 20 threads per inch.
I measured the lead of the thread with an indicator as .050 “/Rev
The step_angle on the motor is 1.8 degrees/Step
Lets see if I can dust off my dimensional analysis stuff here.
I found a really interesting thread here at http://www.eng-tips.com/viewthread.cfm?qid=136950&page=1
This isn’t difficult,but I’m having a brain fart here”
“Pitch is the distance between adjacent thread forms or lead divided by number of starts”
|
lead (Inch/Rev) |
| Pitch(Inch/thread)= |
———————- |
| |
starts(Thread/Rev) |
(Initially I thought I had a muli-start lead screw but it turns out its only single start.)
Pitch X Starts = Lead(Inch/Rev)
|
Lead (Inch) |
|
Step_Angle(Degrees) |
|
1 Rev |
| Linear_step_increment (Inch/Step) = |
——————- |
X |
—————————– |
X |
————— |
|
(Rev) |
|
(Step) |
|
360 Degrees |
For a multi-start thread this would be:
|
|
Pitch (Inch) |
|
Starts(Thread) |
|
Step_Angle(Degrees) |
|
1 Rev |
| Linear_step_increment (Inch/Step) |
= |
——————- |
X |
——————- |
X |
—————————– |
X |
————– |
|
|
(Thread) |
|
(Rev) |
|
(Step) |
|
360 Degrees |
So for my machine
Linear_step_increment = ( (.05 /*1.8)/360 = 0.00025 inch per step
Resolution isn’t to shabby with full step. So… I think microstepping for me is going to be more of an issue with reducing resonance than positional accuracy.
Just to work this out a bit more. According to here
The linistepper and the resulting linear step displacement would be as follows.
200 (full step) 0.00025 Inch/Step
400 (high-torque half step) 0.000125 Inch/Step
1200 (microstep 6th 0.0000417 Inch/Step
3600 (microstep 18th) 0.0000139 Inch/Step
I think that 1/2 step would be fine for my purposes but I suppose taking advantage 1/6 step would be handy if I run into resonance issues.
Positional accuracy is not going to be an issue, but the big problem is going to be speed on the rapid movements
According to the linistepper http://www.piclist.com/techref/io/stepper/linistep/lini_use.htm if I optimize for power consumption, I could expect out 4 Rev/Second out of my steppers.
Originally, I thought I was going to optimize my PSU for power consumption but I’m rethinking this strategy.
I need to go from Rev/Second to IPM
| 12 Inch |
|
4 Rev |
|
60 Sec |
|
.050 Inch |
| ———- |
= |
———- |
X |
———– |
X |
————- |
| Minute |
|
Sec |
|
Min |
|
Rev |
So that’s really really slow…
I found this line in the reference:
The amount of PSU voltage you need is determined by the application. In most cases a voltage of 3x the rated motor voltage will give decent performance through the main resonances up to 10 or 15 revs/second
Ok that’s sort of made the decision for me.
My x-y motors are rate at 6V 1.2 amps/phase
My z-axis motors are rated at 5.4 V 1.5 amps/phase
Rotary Axis motor tbd.
I’m not sure I want to go nuts trying to push a lot of voltage motors but I think using a 12 Volt At power supply is not unreasonable.
So… going to How to “tune” it to suit special needs!
Ignoring the rotary (since I don’t own one at the moment) I’m estimating my PSU requirements will be around:
| X-axis |
1.2 |
X |
2 |
2.4 |
|
| Y-axis |
1.2 |
X |
2 |
2.4 |
|
| Z-axis |
1.5 |
X |
2 |
3 |
|
| Rotary axis |
? |
|
|
|
|
| cooling fans |
0.24 |
X |
4 |
0.96 |
|
|
|
|
|
8.76 |
Amps |
|
|
|
|
105.12 |
Watts |
Thats a little bit of a bummer, I had a PC power supply rate at 12 Volts 6 amps. I having a feeling that this is probably will be ok with usage(Whats the possibility of running all axi simultaneously at full power. I my inclination is to look with something with a bit more oomph to be conservative.
Another this I need to add to my shopping list are fuses.
I found this quote in how to “Tune” to suit…..
A slow-blow fuse rated about 2.5x the max normal phase current (if motor is 1 amp/phase use a 2.5 amp slow blow fuse placed before the linistepper) Fuses are always a good idea!
For me this work out to:
| X-axis Fuse |
1.2 |
X |
2.50 |
3 |
Amps |
| Y-axis Fuse |
1.2 |
X |
2.50 |
3 |
Amps |
| Z-axis Fuse |
1.5 |
X |
2.50 |
3.75 |
Amps |
| Rotary |
|
|
|
? |
|
Now I might as well do some current optimization for my lini-steppers.
On the How to “tune” it to suit special needs! section titled “changing current” there is a calculator
For my 1.5 amp solution I got a perfect match:
Results of resistor set search.
Target Resistance for your current requirement of 1.5 Amps is 0.6666666666666666 Ohms
At the full current, this will dissipate a total of 1.5 Watts over all the resistors, but each resistor will dissipate a different amount, shown in (), depending on it’s value.
Tolerance on search = 1% null (Found 158 sets within tolerance)
The closest match is 1 Ohms @1W paralleled with 2 Ohms @0.5W which is perfect.
For my 1.2 amp drives. This is going to get ugly:
Results of resistor set search.
Target Resistance for your current requirement of 1.2 Amps is 0.8333333333333334 Ohms
At the full current, this will dissipate a total of 1.2 Watts over all the resistors, but each resistor will dissipate a different amount, shown in (), depending on it’s value.
Tolerance on search = 1% null (Found 315 sets within tolerance)
The closest match is 1 Ohms @1W paralleled with 7.5 Ohms @0.133W paralleled with 15 Ohms @0.066W which is perfect.
I decided to try the site referenced at this calculator
http://www.computertorture.com/noncompliant/parallel/index.html
And got this result:
Results of resistor pair search.
Target Resistance = 0.8333333333333334 Ohms
Tolerance on search = 1% (Found 2 pairs within tolerance)
The closest match is 1.2 Ohms paralleled with 2.7 Ohms at only -0.31% out
| First (Ohms) |
Second (Ohms) |
Paralleled result (Ohms) |
Deviation (%) |
| 1 |
5.1 |
0.83 |
+0.32 |
| 1.2 |
2.7 |
0.83 |
-0.31 |
This is basically my shopping list of things I need for this project:
| Need to get list |
| power supply |
8.76 amps 12 Dc with 5 Volt |
| Project Enclosure |
Qty (1) Enclosure |
| Mounting plate? |
Qty (1) plate to mount 4 lini’s |
| 4 Linisteppers 3 per |
Qty(12) Standoff |
| x&y axis |
Qty (2)-3amp Fuses/Fuse holders |
| z axis |
Qty (1)-3.75amp Fuses/Fuse holders |
| Connectors for cooling fans |
Qty(5) |
| Z axis For 1.5 amp current sense resistors |
Qty (2) 2 Ohm (1 Watt Min Rating |
| X and Y axis current sense |
Qty (4) 7.5 Ohms (.266W <Min rating) |
| X and Y axis current sense |
Qty (4)-15 Ohms (.132 W Min rating) |
Lets see what am I forgetting.
Oh yeah… I need a speed controller, and a solenoid with for my Spindle motor and at least consider optical isolation.
