[Agro]

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]

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]

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]

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]

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]

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]

PC Power Supply Linking.
http://www.procooling.com/index.php?...s&disp=52&pg=1

[Jack Aubrey]

Many Thanks Shay!

[Agro]

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]

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]

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]

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]

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]

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]

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]

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]

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]

There have good and inexpensive stepper.

[email protected]

[Jack Aubrey]

Thanks for that sdantonio!

[Agro]

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.