Little testing
 

Thought of testing for backlash by milling the contours of pcb tracks.
Attachment 8044
Roughness is due to me not using proper bit but a broken drill bit as cutter and high feed rate of 100 ipm, whole thing milled in 34 seconds flat :D. See for yourself the capability of MM :D, perfect usable PCB can be produced with proper bit and feed.

May be if I can get a bit I'll do the BoB and cntroller board for MM on MM itself :)

Note : I still need to put the spoil board and surface it.

Question about VFD 0-10v control !
 

Can anyone using VFD with 0-10v speed control unit confirm that a input with about 500mv ripple will work on VFD ?

I tested a simple RC network today and its producing DC 0-10V with a ripple of 500mV from PWM signal at 1500Hz.

How far can we increase the PWM freq from Mach ?

Anil, I'm running off a PWM signal and a simple RC network; never bothered to measure the ripple. The first shot used a very small capacitor, and it showed up as a random small speed variance at the spindle (I had the VFD display the spindle freq). I upped the capacitance until the variance went away.

Assuming that your VFD linearly allocates the 0-10v across 0.0-400.0hz ( mapping to 24000 rpm), it's 10v divided into 400 (or 4000) levels, so 25mv (or 2.5mv) per level, with each level representing 60rpm (or 6 rpm). 500mv ripple could represent up to 1200rpm or 20hz variance, assuming that the VFDs sampling of the control signal was worst case timing with no hysteresis. Real world variance would likely be less; mine was about 3hz before I fixed it.

I suspect you'll want to increase your capacitance a bit, but testing will show you what you need to do. The down side of too much capacitance would be a VFD that was slow to respond to control signal changes.

Thanks Brad, I guess there is bit of hysteresis or averaging or both built into VFDs so don't want to increase cap too much slowing the response time.

That's exactly the reason I asked for how much high Mach can reliably put out PWM freq (assuming 25Khz kernel freq).

Whats your PWM base freq set at ?

I'm using EMC2, not Mach3, and the setting I'm using is 50hz (I just triple checked this, I'm using the pwmgen module for EMC2). Practically speaking, the physical limits of spindle accel and decel are far greater than even lots of capacitance here, as long as you don't use a spare power supply filter cap :). 1500hz should be more than enough.

Thanks Brad for confirming the freq, you are right about the response time in practical world :) I'll increase the cap value to get the ripple down. Bad news is my DSO died suddenly for no reason :(, I suspect the grinding dust from rail grinding got in and shorted something inside.

I can't remember what a DSO is?

Sorry Gerald for the confusion, "Digital Storage Oscilloscope" is not a part of MM, thats the reason you don't remember :)

Hope the scope issue turns out to be something
simple like a fuse.

Can you get the LMD18245T locally?

Quad, I got LMD18245 from farnell (http://in.farnell.com), you need 2 of them for each drive. Micro-controller is also available on same site.

Another PCB
 

Kobus asked if its possible to do isolation milling on MM, I did trail and here is the proof that its surely possible.
Attachment 8057

Note that I am using broken drill for milling, so the isolations are wide and the actual track/pad width looks small. But with actual bit the output is a usable PCB as all tracks are intact :)

By the way this is the actual PCB for MM to combine all inputs.

And with Vectric V-Carve pro I can do the PECK Drilling of the holes at the same time.

Kobus, Eagle generates a NC file for drilling as well. I didn't bother to complete the milling and do drilling as its just a test, for you :D

Anil,,

Your PCB looks good...even with the limitations you talked about. Thanks for showing us more of the capabilities of the MechMate.

I know you may be busy with getting your spindle working and that you have a "day job" to attend to, so this discussion may need to be delayed...BUT, I'm very interested in your experience with the Open Circuit AVRSTMD drivers.

First, could you confirm the specifications of the stepper motors you are using? I believe you are using the 3.5 amp, 4.5 volt, 450 oz-inch HOLD, Superior Electrics for the X and Y and a 300 oz-inch for the Z. Is this correct? What current setting are you using on the AVRSTMD? Also, what voltage are you running the stepper motors at?

Next, I'm wondering about mid-band resonance. I don't believe the AVRSTMD driver design has mid-band resonance compensation. On the other-hand, ALL of the Geckodrive stepper motor drives have mid-band resonance compensation. So, do you notice any problems with your MechMate that would be the result of mid-band resonance issues? I'm no expert, but I believe the effects would be strange noises and even stalls or lost steps.

Finally, I'm wondering about heat. The AVRSTMD uses some significant heat sinks. It appears that your drivers are mounted on metal stand-offs directly to the back of the enclosure. Do you notice any heat build-up inside your enclosure? Did you vent your enclosure? Do you use any circulation fans? I don't see any vents or fans in the pictures of your enclosure.

Thanks and first of all let me make it clear that I wanted to avoid Geckos because of cost (my whole set of drives cost me about the cost of one 203 :)) and believed that if motors are chosen and connected correctly 3Amp limit of drivers chips (LMD18245) is enough for MM.

I am running chips at 2.5 Amps with single coil on x and y and series connected coils on z (because z motor is 4.6 amps).

You won't believe but only Y motor is 450oz-in and all other motors are approx 300 oz-in and I am comfortable at running any axis rapid at 500ipm without loosing steps (of course you can't cut at 500ipm anyway).

I have not noticed any mid-band problem till now, I guess motors accelerate fast enough through the region. May be I need to run slow enough to notice the oscillations. (whats the accel you are using ?)

I've multiple taps on transformer so that I can get 45, 50, 60 volts, I tested drives on 45 and 50 volts.

Though I use large heat sinks on my drives (because I already had many of those laying with me), I think smaller will do, after-all its a DMOS device unlike 298 which generates lot of heat.

I don't have a fan but I have ventilation holes right above the drives, not visible in pics because those are covered by keyboard sitting above them :)

Computer CPU is generating more heat than these drives :), Its winter season so I am not installing the fan right now, may when its hot I'll add one.

I guess you already know, PICstep is another similar option available for drives using LMD18245.

Anil,

Thanks for taking the time to respond to my questions. I appreciate the thoroughness of your response.

I'm planning to build a second MechMate. So, I'm wondering about using the AVRSTMD drives. I think I can build them for $20-30 each.

Keep up the great work! And please continue to share your results with us.

Two more questions. Have you "sensed" the temperature of the drives during operation of the MechMate (like touch them or nearly touch them or measure them with one of these)?
Same question for the motors?

I don't have device for temp measurement, but I can touch them.

Motors are only slightly warm.

I can say that its worth to give it a try as you can build 4-5 of them for the cost of one Gecko and in case you feel you need to upgrade, you can use them for Y,Z,A etc and just but Gecko for X.

I'll do a temp measurement circuit as I get time and do the measurements on drives, inside box and motors.

Also again, do look at picstep as well.

Thanks again, Anil. I'll be interested in your observations once you get your spindle working and start using your MechMate for long cutting sessions.

For temperature monitoring, I purchased a temperature probe like this from Ebay and mounted it in the front panel of my enclosure. I attached the probe end to the driver heat sink.

I'm going to build at least one AVRSTMD. and check it out.

I've programmed both PIC and AVR. I find AVR simpler to program, so I'll go with the AVRSTMD for now.

I also notice that the Geckodrive G250 (which is the module used in the G540) is only $61 each and it can handle 3.5 amps and 50 volts. It also has the mid-range resonance compensation that I mentioned in an earlier post.

Keep up the great work Anil. Your build is an inspiration.:)

Thanks you John and good luck for you next MM.
Installed the spoil board and tried to set gantry at 90 deg to X, not yet done but will do next week as its I think its off more than that can be fixed by shimming the gantry wheels. Need to adjust the Y rails first on gantry tubes a bit before shimming the gantry wheels.

For now before surfacing the spoilboard, wanted to spoil it a bit so here is the cartoon file again :p

Attachment 8107

My first 3D on MM
 

My first attempt at 3D on MM ..
Attachment 8145

Sorry for the bad pictures I always post, my handycam don't do better than this on stills :( , Next time may be I'll try video.

John, the last 3D job is 12x12 inchs approx and took about 50 mins using 4mm ballnose cutting about 0.5" deep in single pass with stepover = d/7 at 150 ipm.

Only Z drive seems getting hot (still touchable) in that an hour time, I think because :
- its the last one in the row, far away from vetilation
- Z motor is 4.6 amp and the coils are connected in series (more inductance)
- and of course its the one doing most work in 3d job :)

I think with a fan blowing air on drives will be sufficient for any cutting job.
Will keep updating as I go :)

Very nice work, Anil. Love the lion's head.:)

I wish I could lend you my Temperature gun. I understand from this Forum that the stepper motors can run safely at 80 degrees C. I think that would feel really hot to the touch...you couldn't hold your hand on the motor.

When you cut the lion's head, what was your driver temperature like?

My cam seems to get better pics in daylight, here is again same pic.
Attachment 8147

John,

Motors run cool with no sign of heating up, all of them only just warm.

While cutting, as mentioned earlier only Z-driver seems to heatup (still can hold hand on it), all other drivers were normal (just warm), Can't give you exact temp figures as not measured, but can say 3 drivers and all motors were warm similar to a Hard Drive running in computer. (may be about 30 deg C)

I'll connect the Z motor as single coil and It'll cool down the driver as other in system. I feel Z is heating up due to very high inductance of Z series connected coils.

John, even with it heating up there was no problem as electronics can run at that temp safely.

congrats again - you seem to be doing it very very well

Thanks, again, Anil.:)

Really great work. Thanks for the feedback on your motors and drivers. Hope all continues to go well for you.

Nice work Anil.

Thanks you all, Irfan, Ken & John.
Now I need nice files to continue cutting :D

Amazing, how tilte of my thread changes automatically :p:D:D

good job, Anil.

BoB Installed
 

Thank you Claus,

Finally got PCBs done and my BoB and controller for proxies and switches installed on MM. Now I can ref home and use the switches finally :)

The charge pump on Bob is done using a tiny micro-controller and same way a controller riding on Gantry takes all inputs from proxies and buttons and combine them to BoB output.

The BoB with charge pump and a simple PWM to 0-10v.
Attachment 8294

The Controller for proxies and switches, the LEDs show the status of Proxies, on estop all LEDS turns on to show if any of the estop button pressed.
Attachment 8295

Back side of board is all mess with all wires coming to connectors.
Attachment 8296

great work

Fantastic! Wish I know how they work.

Hi Anil,

Thats a nice BOB, keep us updated on the perfomance

Vishnu

Thanks you Vishnu/Irfan :)

Ken, Don't understand what you mean ?

If you want to know how its working for me, then yes these seems to be working fine for me :), for now. I'll test it with VFD when I get the spindle and report.

If you want to know how its programmed (ts simple stuff anyway), then for controller on Gantry :
samples all switches continuously and whenever any of "start" buttons is pressed it, it makes "start" output high. same way for "pause" buttons.

Proxy and estop inputs are sampled every millisecond, on estop input the estop line is made low and all LEDs are put on to show the event.

On any of proxy input the proxy output is made low and corresponding LED On to show the status.

(Proxies are not sampled continuously along with buttons, but every millisecond so that the homing sequence is repeatable every time exactly)

On BoB, there are buffers on inputs and outputs with the addition of a simple RC network to convert PWM to 0-10V signal for VFD.

and for Charge pump, there is a tiny micro-controller that counts pulses from CP pin every 10mS (for a frequency in the range of 6KHz to 13Khz), if the pulses are found in the range 10 times successively the outputs are enabled.

Same way on enabled outputs the CP signal has to miss for 10 successive times before the outputs are disabled.

In turn thats 100mS before the outputs are enabled/disabled on valid/invalid signal. I'm sure it won't act on noise with all this :)

By the way, can mach use same input for z-zero sequence as the other proxy inputs ? If yes, then the z-zero input can be combined as well, also the same 2 buttons when pressed together can initiate the z-zero sequence !!!

Anil, Thank you for your detail explanation of the working principle. I'll have to spend some time understanding it.
Woulkd you kindly elaborate the RC tank convert the PWM analog signal? Does the PWM signal comes in the form of pulse train or bit stream? I am having the idea that the PWM is a Psudo Analog signal...

PWM as the name suggest is pulse train of varying pulse widths. For low value the on time is less compared to off time, same way for higher value the on time of pulse is grater than the off time. So if you just average the pulses you will get an analog signal (of course in the range 0-5V).

To get 0-10v output you need to amplify it. I used a transistor to shift the level of pulse to 10v and then averaged.

Now I can see much more clearer. Thanks

I'm so happy!

PCB adapter for SMD part
 

As usual, again showing a PCB done on MM :)
This time made few adapters for surface mount parts for my electronic prototype work.

This pic is interesting because of the sizes involved on smds parts, this pcb is milled using 0.2mm bit and note the track width is only 0.1mm. (calculate that in inches :) )
Attachment 8355

Some tracks are exact width but some are a little wider, Is that backlash ??
Also noticed that the pattern is consistent on all of them

Ouch! that thing is only 1" square! Okay, while the tracks are supposed to be 0.1mm [0.004"] wide, some are twice as wide as others, range probably about 0.05mm [0.002"] to 0.15mm [0.006"], which means you are holding an accuracy of +/- 0.05mm [0.002"]. That is too technical, and it tells us nothing . . . .

Did you always go in the same direction around each pad/track? If you go clockwise around, you will get wider tracks than if you went anti-clockwise, because of the flex in the cutting bit.

Anil,

Well, .1 mm is about 4 mils (.004 inches). Not bad. Nice work.:)

I think I see the pattern...the lines are thicker on the left of the adapter picture...is that what you are seeing? I have no idea why it happens.


Were all the adapters you cut usable? I mean, were any of the signal lines too thin or "open"?