Re: SLO-SYN 12.7 Amp motors

Les Watts wrote:

> From: Les Watts <leswatts@...>
>
> I have finished the mechanics on my big gantry mill and am ready to hang motors. I am faced with big bucks to
> buy 4 axes of servos (400+ in oz peak torque) and amplifiers.
>
> What got me interested in this thread is an acquisition I made today. Due to a facility move at work I got 8
> slo-syn MH112-FJ4201 1200 in oz steppers with 3180-pi mosfet indexers. These monsters give 900 in oz at 4000
> half steps per second and 100 in oz at 20000 steps. Max speed appears to be 2500 rpm. Even with the typical midrange
> stepper torque droop these things have more oomph that my motor sizing software calculated is needed. Inertia match is good too.
> The indexers are rs232 or parallel programmable in EIA L, H, N, G,X, and F codes. They use 20kHz switching supplies and plug in
> the wall. (120v 5A)
>
> I had no intention of using an open loop system on my machine. I have seen the unfortunate effects of
> slipped steps before. That would be fairly violent when one is moving an 800 lb gantry.

Yes, I think you're right.

> I sure would like to save a couple of grand though. Although new or used for experimental stuff only,
> the ten year old indexers run at 9600 baud only. I calculated that my mill has 5.5X10^18 addressable
> locations using 1024X4 renco encoders- sounds like a real bad combination! I don't think the indexers
> can do precise coordinated moves either. Too slow.
>
> I will consider bypassing the indexer and just using the amplifier portion under PC control with
> encoder feedback for at least slipped step detection and correction. Will EMC do this?

they are working somewhat toward that.

> I also got some .5 and .25 hp pm dc 90v motors. With encoders these are a fair match. But no amps
> other than a bunch of SCR speed controls (no good for cnc).

Depending on what speed these are, the .5 Hp could be enough. A low speed motor at 1/2 HP,
or a high speed motor with belt reduction should handle it. I'm using 1/8 Hp (continuous) motors
on my Bridgeport.

> If I don't use the steppers I will need:
>
> 1) 4 10 amp Copley brush servo amps ($1080) or
> 2) 4 Apex PA60 10A hybrid PWM servo driver chips ($520 + a month of weekends fiddling with heat sinks
> and power supplies) or
> 3) Jons amp design
>
> Leslie M.Watts
> Illinois Tool Works
> Corporate Advanced Technology group

Depending on how far you are from St. Louis, you could come down and see my
setup. That might convince you. I will open that offer up to anyone else on this
list. If you'd like to see EMC run a Bridgeport with servo motors, and can drop
by St. Louis, or happen to be in the area for other reasons, let me know, I'd be
glad to show you one that works.

Jon