[Agro]

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]

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/showth...4&page=1&pp=15

Cheers

[Agro]

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]

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]

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]

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]

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]

If you switch over to the opto-isolated BoB wouldn't that ensure that you would have enough voltage pulsing the irfz44's?

[Agro]

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]

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

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]

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]

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]

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]

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]

My calcs have to be wrong. It's been sooo long since I have done this sort of thing - I'll try again

[Madclicker]

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]

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]

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]

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]

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.