Re: Getting Started with Servo CNC

Hey Dan,
Thanks for the reply. I sent you a seperate private email for the
pictures, but figured I'd continue here with the on-topic stuff.

> 1. The hole in the shoptask X axis case is too small for a 600 oz in
> servo and I don't know of an easy way to make it larger without a

lot of

I noticed this, and I am sort of torn between machining entirely new
plates or trying to fiddle with adapters. The too small hole (which
means I have to machine the plates anyhow) is pushing me towards
entirely new plates. Also, I could replace the old ones if I decide
that my servo system is better suited to something else down the
line, and steppers would be fine.

> work. If those are the motors that I am thinking about you will also
> need an external power supply because those encoders draw more than

the

> Gecko's can handle.

Check. I allready built a 1Amp 5V regulated supply for the encoders.

> 2. The motors that you probably got have 500 cpr encoders which

means

> that 500 times 4 for quadrature =2000 per rev. Times 2/1 ratio =

4000

> time 10 TPi= 40,000 steps to the inch. Master 5 is limited to ~8000
> pulses per second so your max speed will probably only be about 12
> inches a minute

After I sat down and started thinking about this I realized this
would be a problem. My current thinking is that I gin up a pulse
multiplier with a PIC or something I have handy to output 4 pulses
per input pulse. I have some concern about putting out clusters of 4
pulses to the servo controller because it may freak out due to the
series of step inputs as opposed to a steady stream of evenly spaced
pulses. I may try to lock onto the frequency of the input stream,
but this is additional complexity.

> 3. The shoptask X axis as I recall comes with a 42 tooth driven

pulley.

> The shaft on your motor is 5/8 D so you will probably need a fairly
> large diameter pulley on the motor losing some efficiencies.

I've been contemplating either boring out the existing pulleys (hub
would be marginal size for set screws), or ordering some bigger ones
for a 1-1 ratio.

A better

> solution would to have been to use the smaller motors that are C23

and a

> have a .250 shaft from Jeff Davis on this list. I have used similar
> motors and gotten over 135 IPM with a 3/1 ratio.

Now this is sounding like a better solution. I'll have to check into
those motors. The further I was getting into these large servos the
more I was feeling like I was trying to make a silk purse and all of
that. I got a decent deal on the large servos and I may someday use
them for something else. I'm married to servos at this point due to
my purchase of the gecko drivers (plus I think its a lot cooler way
to go).

I looked over Jeff's web page, but didn't see them for sale. I have
dropped him an email and in the mean time I'm looking for motors on
ebay.

I also just noticed that you have slightly smaller servos on your
page for $160. I think they still have the problem of the larger
diameter shaft. I believe that a nema 34 stepper has a 3/8" shaft
and the shoptask has a similar sized hole.

> Master 5 is set up to run a mill/gantry system but by swapping the
> motors cables for X and Z you would have a correct configuration

then

> all you need is the CadCam program that will give you the correct G

code

> files for a lathe.

Here's where I know just enough to get myself into trouble. Since my
lathe x and z axis are the same as my mill y and x axis
(respectively) I'm thinking I'll either just have to be careful in my
cad program to arrange things to work properly, or unplug and replug
the cables for the different setups.

I suppose I'll figure out what is best with experience.

Thanks for all your help.

-Erik Reikes