Indexer board capacities

[rlbeal]

What is the maximum speed the boards will run a stepper...steps/second..RPM?

What is the optimum/maximum voltage and amperage to supply the boards with safely?

What is the biggest stepper motor that the boards will run? Nema 34? (an associate has an old machine I would like to retrofit, but the motors are huge)

Will they drive both unipolar and bipolar steppers?

Robert Beal

[bruce_clark]

Mr. Beal:

These are not 100% accurate, but this is my best
calculations:

Maximum RPM for a ShopBot (going ONLY in x, y or
combination of both) is 5700 steps per second
(maximum theoretical) but probably REAL life is
closer to 2000 steps per second. That gives you
a theoretical RPM of 855 or REAL life rpm of
about 300.

The driver chip is rated to 46V MAX input, but
rated at a typical driver voltage of 24V with
a minimum of 10V. The maximum rated current is
3 amps per phase for the driver chip.

Now, for sizing your powersupply's current/amp
capability, the easiest way (assuming you are
using a chopper driver--like SB does) is to
multiply 1.5 times the UNIPOLAR current rating.
So, a motor that is rated at 2 amps per phase,
should have powersupply capable of suppling
3.5 amps of current. This is for just ONE motor.
On a ShopBot machine with 4 driver boards and 4
stand size Vexta motors, your _rule of thumb_
supply should be able to provide at least 14 amps
at the rated voltage.

The boards will drive ANY motor that operates
withing the 46V/3amp phase requirements. You
_could_ drive NEMA 56 stepper motors if their
power requirements fell in the drivers
capabilities. Now, you could also driver motors
that have higher ratings (such as 4 amp per phase
motors) but they would not reacher their rated
torque/speed output) but they would still work
AND _probably_ put out more torque than a smaller
motor running at rated power.

Just one thing about OLDER stepper motors.
Basically, there is almost NOTHING that can go
wrong with stepper motors except the bearings can
go bad (from constant use, poor loading/improper
design, or contamination) OR winding can be
burned out or motor can be demagnetized. This
happens when motors are OVER driven (purposely run
at a HIGHER current than rated for). With that
said, there has been a LOT of development of
stepper motors in the last 5 to 10 years. They
are now using rare earth elements to get more
torque out of smaller motors and other
things such as better design, better manufacturing
ect. So, many older LARGE motors are NOT more
powerful than a smaller NEW motor. So, get the
specs for any motor before you ASSUME it is a more
powerful motors.

Second, check the voltage/current rating of these
motors first. A motor that is rated at 24V and
.1 amps will be a very small/low torque motor. A
motor with a rating of 1 volt and 10 amps will
generally be a VERY powerful (torque wise) motor.
Another rule of thumb is, the lower the voltage,
the faster the motor can turn, while the higher
the current, the more powerful a stepper motor.

Now, to answer your last questions, the ShopBot
driver is a UNIPOLAR driver. It will drive ANY
5, 6, or 8 two phase stepper motor. It will NOT
drive a 4 wire motor, nor will it operate a
3 phase or 5 phase stepper motor.

If you have any other questions, feel free to
email me.

REFS:
SLA7026M data sheet (Sanken)
Rules of thumb: IMS Website, AMP data sheets,
EE friends (who work with stepper
motors/drivers) and powersupplies.

Bruce Clark
bwclark@centuryinter.net (mailto:bwclark@centuryinter.net)

[Ted Hall]

Hi Robert,
Bruce's answers above are correct. We will try and post some data sheets in the developers area shortly so that this information is more easy to obtain. Let me re-iterate a couple.

Using our current Control Board:
Maximum stepping speed will be 2000/steps sec
(requires a 486 in DOS; pentium in Win95/98)

Using our drivers (which are unipolar only):
Max voltage is 46v DC (though other boards where
I've seen the same chips used are rated only to
35). Max Current (which is what's relative to
stepper selection) is 3A. This assumes a very
good heat sink. Driver current is
set by a resistor on the driver board. We
currently run motors between 1.7 and 2.0A
depending on the axis, etc...

Bruce and I have discussed modifying the Control Board to control generic step-and-direction drivers. We will probably add that option, but probably not in the next few months.

A slight modification in micro-controller would allow us to double the step speed. But most of the motors that we use have a power curve fall-off at about 2K, so I'm not clear that we would gain much at this point. (I'll try and get our motor performance curves up here too so you can get a feel for the trade-offs.)

[arthur_ross]

Regarding the 46/35 volt rating, I have noticed that Allegro is a little liberal in their chip specs, so it doesn't hurt to be conservative in your application (I'm afraid it's a case of Sales having priority over Engineering :-) )

Arthur Ross/Deltamation Inc./www.signsontap.com

[toml@starband.net]

I am rapidly closing in on my Junkyard Bot. It will be a Bot that is made from surplus/recycled materials that I got from a junkyard (literally) and surplus out of Ebay and various surplus shops. My goal, which is really just a re-stated version of your original goal, is to build a really inexpensive machine that is accurate and will do valuable work.

I am using NEMA 42 frame motors. At 12V they are running at 2.5 amps measured. They seem to provide enough torque to move the carriages with good authority.

I have just come heir to a NEMA 42 motor that has 850 Oz. torque. (snort, grunt, MORE POWER) How could I run another driver that would be in the 5 amp range?