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Agro
04-10-2006, 08:48 PM
I have caught the bug...

I actually read about a CNC build on another site and eventually stumbled across cnczone - I've caught the
bug and feel the need to build ;) I'm a programmer by trade so this will be something of a departure from
what I have done before - should be a lot of fun ;)

Current Phase: Planning

I am planning a fairly stock standard JGRO for my first CNC. The only departures from the plans will be
adapting for metric materials (i.e. 18mm MDF) and where components are proving difficult to source in
Australia. The current phase is researching materials and availability, this is actually proving difficult
in the limited market we have over here.

On the up side, Australia deals in both Metric and Imperial measures with the imperial components usually
being considerably cheaper. So with the exception of the MDF I shouldn't encounter any problems there.

This will be a budget job, so I expect it will take many months to get all the bits I need.

One thought was to use aluminium plate for the adjustment blocks - cost is a prohibitive factor there as few
seem willing to supply small amounts of plate. I may resort to wielding these up out of 1"x1/2" steel boxing
as this seems to be the weakest part of the system.

Supplier
Component
Approx Cost


Bunnings (i.e. hardware house)
MDF 18mm 1600x1200 sheet - AU$64 (*2=$128)
All-Thread Rod 45"* 5/16-18 - AU$ 8 (*2=$16)
Aluminium Angle Extrusion - AU$5 ($5)
Screws/Bolts/Glue - AU$50 ($50)


Miniature Bearings INc
Roller Blade Bearings (pkt 10)- AU$14 (*3=$42)
Delrin/HDPE Rod 25*300 ($14)
Flanged Bearings $20 ($20)


Oatley Electronics
CNC PC Interface (K142A) AU$27 ($27)
Stepper Motor Controller (K142B) AU$25 (*3=$75)
Constant Current Power Supply (K142C) AU$29 (*3=$87)

Southern Steel Cash and Carry
Black Pipe (1" and 3/4" - no stock on 1/2") AU$??


TBA
======================
Stepper Motors (what size for a standard JGRO?)
Power Supply (30v)
Acme all-thread instead of the above.



There's probably a lot more to add here...

Cheers
Jason.

EDITS

1. Changed all-thread type based on recommendations. though I will go the Acme if I can find it. Also updated component list.

phillby
04-11-2006, 07:26 PM
Hi Agro,

Welcome to the Zone.Oz is a big place where are you. I'm Sydney Quaker's Hill.

I too Built a JGRO and have developed some modifications as the zone generally developed ideas that seemed oveall to improve the machine. My build log dealt mainly with the electronics and the mods to improve the rigidity of the design.

See the log
http://www.cnczone.com/forums/showthread.php?t=11814&page=1&pp=15

Cheers

Agro
04-11-2006, 07:36 PM
I saw your build log and have every intention of stealing a few ideas ;)

I'm based on Croydon but spend a lot of time getting my house in Marayong ready to be rented out, I'm also currently working in Norwest and will be for the next few months (contract) - so I'm only a short distance from the quackery daily at the moment.

I would love to see your machine in action and see how you went about the project. I'll send you a PM.

Cheers
Jason.

Jason Marsha
04-11-2006, 09:16 PM
If you are going to use allthread rod go with the 5/16-18 instead of the 1/4-20.
The 5/16-18 rod will fit nicely into the the skate bearing hole.

Jason

Agro
04-12-2006, 12:00 AM
I have found a local supplier for Acme all thread. He can only get in sizes 1/2" or larger, the 1/2" is 6TPI.

At 6TPI it shounds like ball screw material to me.

The best part - only AU$100+GST for a 6 foot length. A *lot* dearer then the standard all-thread, but very tempting regardless of the budget.

Question - is 6TPI too low a thread count ?

Cheers
Jason.

Agro
04-17-2006, 07:14 PM
Planning is progressing. I have found suppliers for most components and have started cutting out the MDF parts.

One thought was to make the MDF adjustment blocks, drill a larger hole then normal and 'sleeve' the bolt holes and the mdf block in carbon fibre. When the resin has set this can be re-drilled and tapped, and I suspect this would be substantially stronger than MDF alone. As I have access to carbon fibre fabric and resin...

Any thoughts - has anybody done something similar ?

Cheers
Agro.

Agro
04-19-2006, 07:17 PM
Ok - Starting to BUILD :)

I have decided to go with one of the open source BOB and Driver designs from this site as it looks like I can build the electronics for less than half the cost of the commercial kits and solutions. The hardest part was finding an affordable source for some of the components.

I have decided to go with The 4 Axis PC interface the discrete single axis stepper driver with three axis (?axi?) for now.

http://pminmo.com/4axis/4axisinterface.htm
http://pminmo.com/discrete/discrete.htm

The only difficulty with the above is sourcing the IRLZ44 FET. Locally they cost >AU$9 each. I can get the IRFZ44 for AU$1.20 each so will go with that, if I have a problem with the gate voltage from the parallel port I will add a driver board at a later stage.

I plan on making the PCB's tonight so we shall see how this goes.

I managed to pick up some recycled stepper motors at a good price. I have been told they are 150oz/in, although I suspect they are not quiet that strong. Hopefully the steppers are strong enough for this project.

Cheers
Jason.

ShayArnett
04-19-2006, 09:05 PM
If you switch over to the opto-isolated BoB wouldn't that ensure that you would have enough voltage pulsing the irfz44's?

Agro
04-19-2006, 09:12 PM
Possibly. I am considering it pending the pricing on the Opto's.

I have a large supply of small three legged fuses (trannies) at home so I will more likely resort to using those to drive the FET's.

No reason other than it is what I have available.

Cheers
Jason.

Agro
04-20-2006, 02:23 PM
Ok - I have just had a seizure... I just calculated the size of the current limit resistors that would be required for my steppers. Unless I have made a significant stuff up in the calcs (verified by steppercalc):

Steppers
=======

Type: Sanyo Denki Step-Syn 1.8v 3A 1.8deg/step

phase current (A): 3
coil voltage (V): 1.8
coil resistance (O): 0.60


Power Supply
==========

I had planned on the two PC power supply conversion - so 24V 20A (I think)... By my calcs I will require 23.4 Amps to drive all three motors... That sounds like a whole lot of power.

Current Set Resistors
=================

Based on the above, using a single resistor I would require:

Optimal Resistance: 3.7ohms
Max Resistance: 3.81ohms
Power Rating: 173W :eek:

Ok.. Let's try for multple resistors (2):

Optimal Resistance: 7.40
Max Resistance: 9.62
Mon Power: 87W

That's some damn big resistors.. Using aluminium housed wirewound resistors approx $50 per motor - I think I need to revisit the drivers I had been planning to use.

Do the above figures seem right - I think they are and am a little stunned...

The constant current drives from oatley electronics suddenly seem far more reasonably priced.

ShayArnett
04-20-2006, 02:43 PM
I'm building the a3977 boards (choppers) but they won't do the 3 amps your motors require. The picstep should handle them but i think they are a little more expensive to build. I would definately go with a chopper though, especially if you haven't invested any money yet.

phillby
04-20-2006, 06:44 PM
Agro
The current limiter is needed in each individual motor supply. IE the actual leads to the motor.

I Used Pminmo 3977 circuits the current max is 2.5A on these.

Yes the Picstep is capable of the 3A You need and it is an Aust design. There are testimonies all over the Zone on the work Alan has done on this Design.

By the way a supplier for electronic bits is

http://www.futurlec.com.au/Components.jsp

They have an office in Melbourne but the goods are shipped from Thailand
about 10 days for $4.00 quicker if you pay more.

When ya gunna look at my machine.

Agro
04-20-2006, 07:15 PM
I will look at the PICSteps thanks guys. I was starting to design an addition to the power supply to implement current limiting via a couple of power trannies, although I could see this generating a lot of heat.

How's one night next week sound Phillby ?

Cheers
Jason.

CanSir
04-20-2006, 07:54 PM
Steppers
Type: Sanyo Denki Step-Syn 1.8v 3A 1.8deg/step

phase current (A): 3
coil voltage (V): 1.8
coil resistance (O): 0.60


Hi. I'm a complete idiot when it comes to electronics and this is my first post in these forums so please keep that in mind, but I think your calculations are off. Only when stalled will your steppers draw the full 3 amps they are rated for so if you happen to stall all three axis simultaneously (!) then you'd still only need a supply capable of delivering 9 amps which is nowhere near the 20amps you were worried about. I read somewhere that it's best if your supply is only capable of delivering 67% of the max current requirement and I can see why that would work as a minimum requirement, but I can't see why it would be the "best".

Here is what I came up with for current limiting resistors:

Total Resistance = Voltage of power supply (24v) / Motors rated current (3a)
Total Resistance = 7 Ohms

Resistor's Value = Total Resistance (7 Ohms) - Motors Rated Resistance (0.6 Ohms)
Resistor's Value = 6.4 Ohms

Resistors Voltage Drop = Motors Rated Current (3a) x Resistor's Value (6.4 Ohms)
Resistors Voltage Drop = 19.2v

Resistor's Power Rating = (Resistors Voltage Drop of 19.2v / Motors Rated Current of 3a ) x 2 (I believe this is for the number of phases??)
Resistor's Power Rating = 12.8 watts


My understanding then is that if you're running the motors off of a 24v power supply, you would need (ideally) four 6.4 Ohm/12.8 watt resistors per motor (one resistor for each coil). Incidently, I've read that the ideal supply voltage should be at least 20 but no more than 25 times the motor's rated voltage. In that case, you have the perfect motors (20 x 1.8v = 36v) for connecting three power supplies in series but then you'd need 11.4 Ohm/22.8 watt resistors.

Can anybody confirm or correct my calculations?

Agro
04-20-2006, 09:59 PM
My calcs have to be wrong. It's been sooo long since I have done this sort of thing - I'll try again ;)

Madclicker
04-20-2006, 10:33 PM
Here is what I came up with for current limiting resistors:

Total Resistance = Voltage of power supply (24v) / Motors rated current (3a)
Total Resistance = 7 Ohms

Resistor's Value = Total Resistance (7 Ohms) - Motors Rated Resistance (0.6 Ohms)
Resistor's Value = 6.4 Ohms

Resistors Voltage Drop = Motors Rated Current (3a) x Resistor's Value (6.4 Ohms)
Resistors Voltage Drop = 19.2v

Resistor's Power Rating = (Resistors Voltage Drop of 19.2v / Motors Rated Current of 3a ) x 2 (I believe this is for the number of phases??)
Resistor's Power Rating = 12.8 watts

Can anybody confirm or correct my calculations?


V/A=R

24/3=8

Resistor:

R=8-0.6=7.4

Power:

P=VI=I*I*R

P=66.6W

Choose 2 100W per motor.

The 2/3 PS figure that people use is based on the fact that rarely are all phases energized at the same time. In this case:

2/3 * 18A = 12A

Now, someone tell me where I went wrong...lol

Agro
04-20-2006, 10:41 PM
Thanks Guys.

For the cost of 2 100W resistors per motor I may as well go for one of the drivers with current limiting. The PICStep is looking promising at this point.

Cheers
Jason.

CanSir
04-21-2006, 12:16 AM
V/A=R

24/3=8

Resistor:

R=8-0.6=7.4

Power:

P=VI=I*I*R

P=66.6W

Choose 2 100W per motor.

The 2/3 PS figure that people use is based on the fact that rarely are all phases energized at the same time. In this case:

2/3 * 18A = 12A

Now, someone tell me where I went wrong...lol

Yep, 24 divided by 3 is definately 8 and not 7. :drowning:

I'm wondering if that last line of the formula I used had the multiply and divide mixed up?

Resistors Power = (R Voltage drop x Motor current) / 2

Since voltage drop is I*R, multiplying voltage drop by the current again is the same as P = I x I x R. The divide by two then makes sense because the formula is designed for using 4 resistors instead of 2.


Agro is right though - it's cheaper (and easier) to just buy a current limiting controller!

phillby
04-21-2006, 08:22 AM
I don't mind but it is a short week. I am tied up Thursday's & Friday's. So as Tuesday is Anzac Day Monday or Wednesday would be suitable.

Agro
04-26-2006, 09:56 PM
Some progress.

I'm busy making the BOB and Driver boards. It's been a long time since I have fabricated a PCB - fortunately I still have my exposure box and the photo resist I have still works even though it is 5 years out of date!. I'm using a solution of 5 mils caustic soda to 1.5 litres of water to develop the boards as I'm too cheap to pay for developer. Works well :)

I won't bother with tinning the boards - instead I will add a layer of spray on lacquer to prevent oxidation, the stuff I have solders through easily - another relic (ref resist).

I have opted for the PICStep drivers and the 4 axis BOB as I plan to add a rotating axis at a later stage. I just ordered the LMD18245's so hopefully they will show up in a week or two.

The woodworking was progressing, although I am going to throw out all of the adjustment blocks and start on those again. It is what I deserve for not taking the time to properly align the triton workbench...

I have opted for 3 PC power supplies (250 watt) as I can buy these from a local recycling centre (reverse garbage) for $2 a piece.

I will hopefully get to spend some time re-making the adjustment blocks this weekend.

Jason.

Agro
04-28-2006, 08:41 AM
I threw away the old chemicals and used some new pre-coated boards. A much better result. For any Aussies - the pre-coated boards they sell at Dick Smith are the perfect size for both the Pickstep and the 4 axis BOB. Probably not a coincidence (Alan ?)

Well.. The first of may build steps. I'll drill tomorrow and should have all the components for the picstep and BOB assembly next week.

Agro
05-01-2006, 01:33 AM
All going well.

I am thinking of building the table and Y Axis support out of Unistrut, and doing a modified JGRO gantry on top of that. I guess it's time to learn to use a CAD package, given the unistrut parts are available this could be a go.

Not the cheapest route, but I get the feeling the end product will be better for it.

I will have a go at desiging the base structure with unistrut and see how it turns out.

I have also moved away from the PC power supply for the electronics. I will use an appropriately sized toroid/rectifier/cap solution for the power supply, I should be able to build a good power supply for AU$100.

Agro.

Agro
05-02-2006, 01:43 AM
As people seem to like pictures I have attached a very rough design for the unistrut base and Y Axis rails.

The diagrams are not to scale - I haven't mastered that aspect of CAD packages yet. (for that matter... I used visio as I don't actually own any cad packages).

I would appreciate any thoughts on the design so far. I will convert to a CAD package and scale when I can. I probably need to add a diagonal supports to protect against lateral movement (collapse).

Agro.

sdantonio
05-02-2006, 04:26 PM
Argo,

Looks like you making PicStep boards. One of the other threads has had several people mention that they haven't been able to get the high torque PIC software to work. But the regular torque works fine.

Steven

sdantonio
05-02-2006, 04:43 PM
Also keep in mind that the cable running from the BOB to the picstep has to be reversed (check the pinout carefully).

Good choice on BOB, the opto boards Phil has are running to slow.

Jack Aubrey
05-04-2006, 11:42 AM
Hi Agro

I'd be grateful if you could show how you use 2 PC PSUs to give 24V DC supply. It sounds like a cool idea - especially as I have about a dozen of them gathering dust around the house!

Belated thought - could you gang 3 of them to add 2 x 12 volt and 1 x 5 volt to give 29V?

Cheers

Jack

ShayArnett
05-04-2006, 12:48 PM
PC Power Supply Linking.
http://www.procooling.com/index.php?func=articles&disp=52&pg=1

Jack Aubrey
05-04-2006, 11:33 PM
Many Thanks Shay!

Agro
05-09-2006, 12:04 AM
Power supply Biult :)

I opted for a 300watt toroid based power supply. This setup is now delivering 26v and should push approx 16 amps to power my 1.8v 3 amp steppers. I know I could have driven higher on the voltage but this seems to be the best price/performance option at this time.

I think I should add more capacitance to the PSU filters. Currently 8000uf, I suspect 30,000uf would handle the demand better when the steppers are working. I'll see what I can pick up.

The PSU is housed in an old rack mount PC case and there is plenty of room left over for the drivers. The (almost complete) BOB can be seen at the back of the case. As currently configured each stepper is individually fused.

Some piccies attached :)

Jack Aubrey
05-09-2006, 01:18 AM
I am going the PC PSU route - the link that ShayArnett gave me is a cracker. I have also just bought an IBM dual rack mount PSU on Ebay for £10 (around 16$US)!

However, for my own education... Why toroidal transformer? Are they more efficient than the more common boxy types?

Also, forgive my newbieness(?) but, what does the BOB do?

Agro
05-09-2006, 02:44 AM
A toroidal transformer is much the same as a traditional transformer. As I understand it the torroidal shape of the ferrite core and the associated windings are far more efficient compared to traditional transformer designs. Toroidal transformers are more compact and produce less noise (hum).

As to why this is the case - beyond my high school science I'm afraid.

The toroid is the large, round, silver component in the case photo above.

The BOB (Break Out Board) provides the parallel connection to the PC and provides a number of connections for switches and the stepper drivers. There are a number of BOB designs available on this site.

Agro.

Jack Aubrey
05-09-2006, 03:43 AM
Thanks Agro. High school science well up to the mark! I have a Xylotex 4 axis board that has the BoB built in so no worries. If you saw some of my soldering, you'd know why I buy rather than build!!

CurtisU
05-09-2006, 06:28 AM
Agro, Thanks for sharing your build with us.

How do you, and others, deal with protection of the parallel port. I've read recommendations that an optoisolator be used (isolate the driver/motor circuits). Is it not an issue with choppers? I've not stumbled across any sources for optoisolators.

I've used, with great success, transient voltage suppressors (diodes) on data lines that had a history of damage from lightning surges. I'm considering using these... a passive approach.

Curtis

Agro
05-09-2006, 08:16 AM
There is an opto isolated board in the open source section. I have heard there are performance issues at high speeds. The 4 axis BOB doesn't have any isolation so there is a risk to the parallel port. I'm not overly worried though.

Cheers
Jason.

ger21
05-09-2006, 08:25 AM
Fwiw, I believe I've only heard of a single incident of a PC being damaged through the parallel port, isolated board or not. In about 4 years of reading this forum and a few Yahoo groups, just about every message, every day. So while some people will insist that you need isolation, from what I see, it may not be that big of an issue. Although I believe it can help with noise issues, if they are a problem.

Jack Aubrey
05-09-2006, 08:39 AM
I am a keen aeromodeller and use iso-optilators (!) on my larger aeroplanes. There can be problems with long wires, like signal and power wires for the control surface servos, engine ignition systems etc, picking up noise from a variety of sources. My local club flying site has a cell phone mast within about 400 metres and definitely causes 'glitches'. I have also had trouble from some cheap servos creating noise which feeds back to the receiver and then corrupts control signals to other servos. So optos for model RC are more for signal filtering than for for voltage protection. They are now used very extensively as is reflected by their price - PD cheap. They certainly cannot do any harm!

On the other hand, if anybody overvolts a stepper controller board, I guess that it is likely to command their attention (and finances) such that they won't be keen to repeat the error!

Has anybody any experience of optos solving any control problems with stepper control systems?

sdantonio
05-09-2006, 09:09 AM
Also, forgive my newbieness(?) but, what does the BOB do?

Hi Jack,

The BOB can do several things. First and formost it is an interface between the computer and the stepper drive boards. It can be a straight link (in which you have to be careful of your groung configuration and make sure it is done right), or it can be opto-isolated (in which case your grounds and be a little more sloppy). It makes the connections neater looking and more organized. Xylotex has it built into the 3 and 4 axis boards themselves. In the case of the PicSteps, it allows you to come in with 1, organized ribbon cable connection between the BOB and each driver instead of having to chase down 4 connections per board from the DB25 cable comming from the LPT port of the computer. There is a guy on ebay, hubbard cnc, who is selling a basic, bare bones bob for about $30 with shipping. Phils 4 axis board does much more (more versitile, not to mention cheaper) and is something you would be much happier with int he long run ahen you later decide to set up limits and e-stop etc.

It is also the place where you attach your e-stop and limit switches should you wish to use them.

Steven

stevenmotor
05-09-2006, 12:42 PM
There have good and inexpensive stepper.

mct.motor@msa.hinet.net

Jack Aubrey
05-10-2006, 02:59 AM
Thanks for that sdantonio!

Agro
05-14-2006, 10:42 PM
An update :)

I had a couple of days off last week so I took the opportunity to build some of the electronic bits for the project. I had hoped to do some work on the gantry but ran out of time.

In the past week:

1. Built the power supply.
2. Built the 4 axis BOB.
3. Built the PICSteps.

I am working on fitting all of the bits into an old all-steel rack mount PC chassis I have and should have this mostly completed this week.

Some specs:

Power Supply
=========
I have opted for an unregulated power supply. The final solution actually incorporates 2 transformers with the primary transformer provides the power for the steppers and a small secondary transformer to provide power for the BOB, PICSteps and a number of fans to keep the system cool.

Primary Supply:
27 Volts, 16.5 Amps fully rectified.
32k uF capacitance on the supply (2K/Amp).

Secondary Supply:
13.5 Volts, 1 Amp fully rectified.
4700uF capacitance on the supply.

Boards
====
As reported the BOB and Picsteps have been assembled - pending a couple of terminal blocks to complete the PICSteps that is ;)

The PICSteps were running fairly warm @ 3 amps. As a result I will be adding a reasonably large heat sink to each driver and a system fan to keep the driver boards cool. I was temporarily/accidently over-driving the LMD's (3.5 amps) however they seem to have survived intact. The current limit resistor is set to 6k8 which is the closest I could find to 6k6, so they should deliver a little over 2.9 amps to the steppers.

one hint is to solder pins to the UNDERSIDE of the picstep boards, then to solder the current limit resistors to these pins. Easier access than the top of the board so you won't be burning a hole in the caps on top. I will post piccies of this later.

The BOB is being wired with the 'Break' on the emergency stop line. I will also wire the emergency stop to one of the parallel port lines to signal the software, and add a solid state relay to turn off the router if the switch is activated.

One issue - I am having to drive my steppers *very* slowely (2mm/s) - 120mm/minute. Any faster than that and I tend to get missed steps or stalling on the steppers. These are small steppers (100-150oz/in) and are only intended to get up and running, but I did expect more than that. I may look at converting the steppers to 8-wire to see if this helps.

All in all - I have had a lot of fun to date :)

Agro.

Agro
06-01-2006, 01:32 AM
Time for an update!

Man have I been busy over the past month. Doesn't matter - this weekend it's time to brew some beer and make more of the parts for the CNC :)

So far...

1. PICSteps created. Some problems with one of the PICSteps due I suspect to a dud chip. The replacement chip has arrived so these should all be up and running this weekend.

2. Power supply created and can be reconfigured as required from 25v 18 amp to 50v 9 amp in a few minutes. A little longer if the current limiters need to be changed on the picsteps.

3. Started on the Gantry...

I have started cutting and drilling the MDF. I wound up throwing the first few peices when I realised the saw on my triton workbench was way out of alignment resulting in some very off measurements.

Finding imperial taps seems to be difficult in australia these days. I improvised by grinding a few cuts in a 1/4 inch bolt and this is working a treat - I'm surprised how strong the superglue/tapped MDF is. If I do have any problems I will fall back to MDF/Chipboard screws and liquid nails, I don't think I will have a problem at this point.

I also managed to get the HDPE I wanted for the adjustment blocks. All of the blocks cut to size for the CNC for A$24 which I'm happy with. All I need to do is cut the hole, drill and tap.

I'm planning on using the offcuts (i.e. the hole) for the anti backlash nuts. Failing that I will get some more of the HDPE to make em.

Once I'm at a position for a photo op - I'll post some.

Plans
====

Some key plan changes...

1. I will buy some better bipolar steppers when I get closer to completing the build. The small steppers I have now will do for prototyping/testing.

2. Based on feedback from Phillby and after seeing his setup I will be looking at supporting all of the rails in the build. I'm not sure what I will do yet, I just know I'm going to do it ;)

3. Continually adjusting for differences due to MDF only being available in metric sizes in Aus (18mm). I made a couple of parts without the necessary adjustments and may need to bin em.

Cheers All

Jason.