Homebrew PCBs

Electronics are a new area of interest for me (my skills lean toward 
mechanical design and fabrication, although I'm relatively 
comfortable with programming). A CNC project has forced me to dive 
head on into this world, and I'm in need of some tips to start out.

For example, I have a need to route the output of my drives on the 
basis of a three-position switch: e.g. "Off | Mill | Lathe". 
When "Mill" is selected, one group of output terminals become "live", 
when "Lathe" is selected, a different group becomes live.
I could almost handle this if all outputs were 5V TTL signals. 
Unfortunately, only 7 of the 9 are. The other two drive the motor at 
up to 80VDC @ 20A. This is clearly beyond simple signal switching, 
and I don't have the experience in power circuit design to figure out 
how to proceed.

Another, perhaps simpler puzzler for me is how to take a 17VDC, 4A 
unregulated signal and produce both a 5VDC & 12VDC regulated signal 
from it. Presumably, it's a matter of finding suitable voltage 
regulator ICs, but even approaching a simple circuit like this 
completely solo has me a little nervous.

I realize this forum might not be the right place to post such 
questions, so what is the appropriate place? While I'm open to book 
suggestions (and am plowing through a ton right now), I really 
appreciate the human interaction and practical advice that are best 
found on forums. Any suggestions? Are there professionals out there 
who offer design services for simple stuff like this at reasonable 
prices?

Thanks in advance for any tidbits you're able to throw my way.

On Friday 22 September 2006 01:18 pm, bigjamma wrote:
> For example, I have a need to route the output of my drives on the
> basis of a three-position switch: e.g. "Off | Mill | Lathe".
> When "Mill" is selected, one group of output terminals become "live",
> when "Lathe" is selected, a different group becomes live.
> I could almost handle this if all outputs were 5V TTL signals.
> Unfortunately, only 7 of the 9 are. The other two drive the motor at
> up to 80VDC @ 20A. This is clearly beyond simple signal switching,
> and I don't have the experience in power circuit design to figure out
> how to proceed.

thats not good
disconnecting the motors while the system is powered up will blow
the drives pretty much instantly

you'd be better off getting the extra drives so you have one for 
each motor ,using separate power switches for mill and lathe
and putting a switch box on the TTL signals only

Brian
-- 
"Nemo me impune lacesset"

>Another, perhaps simpler puzzler for me is how to take a 17VDC, 4A 
>unregulated signal and produce both a 5VDC & 12VDC regulated signal 
>from it. Presumably, it's a matter of finding suitable voltage 
>regulator ICs, but even approaching a simple circuit like this 
>completely solo has me a little nervous.

 

How many amps are you looking to pull through the 12 and 5 VDC lines?

 

>Len







[Non-text portions of this message have been removed]

On Fri, 22 Sep 2006 22:18:22 +0200, bigjamma <bigjamma@...> wrote:

>
> For example, I have a need to route the output of my drives on the
> basis of a three-position switch: e.g. "Off | Mill | Lathe".
> When "Mill" is selected, one group of output terminals become "live",
> when "Lathe" is selected, a different group becomes live.
> I could almost handle this if all outputs were 5V TTL signals.
> Unfortunately, only 7 of the 9 are. The other two drive the motor at
> up to 80VDC @ 20A. This is clearly beyond simple signal switching,
> and I don't have the experience in power circuit design to figure out
> how to proceed.

maybe contactors (relays) will be best, you won't need to switch rapidly  
and very often?
Watch inductive kickback from the motor with any sort of switch, but  
contactors are most tolerant to abuse.
Also make sure you don't kill the drivers, some stepper drivers like to  
die if you disconnect the motor.

> Another, perhaps simpler puzzler for me is how to take a 17VDC, 4A
> unregulated signal and produce both a 5VDC & 12VDC regulated signal
> from it. Presumably, it's a matter of finding suitable voltage
> regulator ICs, but even approaching a simple circuit like this
> completely solo has me a little nervous.

Yes, regulators, either linear or switching, depends on how much current  
you need etc..

> I realize this forum might not be the right place to post such
> questions, so what is the appropriate place?

This is xactly the right place.


ST

>The other two drive the motor at 
>up to 80VDC @ 20A.

Matches a Gecko G320 servo drive. Whatever, switching contacts in 
the range 20A@80VDC would seem to be in order. But if it's the G320 
then you can get by with a lower rating than that. IIRC, 20A is the 
current it trips at so this is a peak rating not a continuous 
rating. Also, will you ever be using 80VDC motors?

Once you've decided on the contact rating, I would recommend 
115/120VAC relays/contactors driven by an appropriate solid state 
relay. The SSR would only need TTL voltage levels for control. Here 
is one being used to control a 3.5A 120VAC drill motor in my CNC 
drill setup;

http://www.pbase.com/eldata/image/46673208

The wires on the left are in the 120VAC circuit and on the right is 
the TTL level circuit. Note the part number and look it up on 
Digikey's web site for zero crossing and snubber features. You 
should be able to get by with one with a lower current rating based 
on the relay/contactor coil current but keep the other features.

You should post this in the Electronics 101 forum if you haven't 
done so already.

--- In Homebrew_PCBs@yahoogroups.com, "bigjamma" <bigjamma@...> 
wrote:
>

On Sat, 23 Sep 2006 11:04:00 +0200, Stefan Trethan <stefan_trethan@...>  
wrote:

>
>> I realize this forum might not be the right place to post such
>> questions, so what is the appropriate place?
> This is exactly the right place.


Oh sorry i didn't spot that this was not on E_101.
It belongs there of course ;-) (Thanks Derek for mentioning that)

ST

>thats not good disconnecting the motors while the system is powered 
>up will blow the drives pretty much instantly

A separate 5VDC supply dedicated to control and a simple electronic 
interlock can prevent switching in the presence of the 80VDC. That's 
provided he goes for all TTL control as I suggested.

--- In Homebrew_PCBs@yahoogroups.com, Brian Pitt <bfp@...> wrote:
>

--- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" <eldata@...> wrote:
...
> You should post this in the Electronics 101 forum if you haven't 
> done so already.

Yes, electronic design questions should be posted there, not here.

http://groups.yahoo.com/group/Electronics_101

Steve Greenfield
listowner of Homebrew_PCBs and Electronics_101

--- In Homebrew_PCBs@yahoogroups.com, "Steve" <alienrelics@...> wrote:
>
> --- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" <eldata@> 
wrote:
> ...
> > You should post this in the Electronics 101 forum if you haven't 
> > done so already.
> 
> Yes, electronic design questions should be posted there, not here.
> 
> http://groups.yahoo.com/group/Electronics_101
> 
> Steve Greenfield
> listowner of Homebrew_PCBs and Electronics_101
>
Thanks for the responses so far, everyone! I'll move the post over 
there (had never heard of that group, so thanks).

Quick responses to the questions asked so far:
 - Yes, this is the Geckodrive G320 servomotor drive. I'll be using 
72VDC motors with 8.3A continuous draw. My power supply is indeed 
capable of producing 20A, so it's possible under heavy strain of a 
single axis that a single drive could see 20A peaks.

 - For the 12V & 5V lines, I'd be looking at being able to supply at 
least 1.5A, although the reality in use will probably be fractions of 
an amp (logic circuitry, Gecko G100 pulse generator, limit switches 
and encoders will be feed off of these supplies).

>Quick responses to the questions asked so far:
> - Yes, this is the Geckodrive G320 servomotor drive. I'll be using 
>72VDC motors with 8.3A continuous draw. My power supply is indeed 
>capable of producing 20A, so it's possible under heavy strain of a 
>single axis that a single drive could see 20A peaks.

Hopefully Steve will allow me one post on this subject. I don't
belong to E101 as yet.

You may wish to join the CAD_CAM_EDM_DRO Yahoo group, too. This sort
of thing is right up their street, and there are folks there using
Gecko's in many different configurations.  Mariss Freimanis, the
designer/producer of Gecko drives, is a frequent contributor
there as well.

Here's the email add'y from his postings:

mariss92705@...

Good luck!

Ron Yost

--- In Homebrew_PCBs@yahoogroups.com, Ron Yost <musik42@...> wrote:
>
> >Quick responses to the questions asked so far:
> > - Yes, this is the Geckodrive G320 servomotor drive. I'll be using 
> >72VDC motors with 8.3A continuous draw. My power supply is indeed 
> >capable of producing 20A, so it's possible under heavy strain of a 
> >single axis that a single drive could see 20A peaks.
> 
> Hopefully Steve will allow me one post on this subject. I don't
> belong to E101 as yet.
> 
> You may wish to join the CAD_CAM_EDM_DRO Yahoo group, too. This sort
> of thing is right up their street, and there are folks there using
> Gecko's in many different configurations.  Mariss Freimanis, the
> designer/producer of Gecko drives, is a frequent contributor
> there as well.

I have not visited that list in quite a while, but when I read
regularly there they were -very- strict about staying on topic. Just
an FYI.

If you look in the Links here, under Related Lists and Forums, there
are a few CNC forums. Including two started as spin-offs from
Homebrew_PCBs.

CAD, CAM, EDM, DRO list
Very focused list about building many times of homebrew CNC machines.
http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/

CNC PCB Design
Building and using a CNC mill to make PCBs and related parts. Started
by Dave Mucha as a companion list to Homebrew PCBs to move the CNC
specific stuff to it's own forum.
http://groups.yahoo.com/group/CNC-PCB_Design/

DIY-CNC
Building your own CNC machine. Mill PCBs, cases, parts, etc. Started
by Ballendo, a great companion group to Homebrew PCBs.
http://groups.yahoo.com/group/DIY-CNC/


Steve Greenfield

>If you look in the Links here, under Related Lists and Forums, there
>are a few CNC forums. 

There's also;

http://groups.yahoo.com/group/geckodrive

--- In Homebrew_PCBs@yahoogroups.com, "Steve" <alienrelics@...> wrote:
>

--- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" <eldata@...> wrote:
>
> >If you look in the Links here, under Related Lists and Forums, there
> >are a few CNC forums. 
> 
> There's also;
> 
> http://groups.yahoo.com/group/geckodrive

Then you should add it to the Links!

Steve Greenfield