[Torchhead]

Here are some numbers to stick in for consideration. Under moderate load the motors are limited to about 500 to 600 RPM with a microstepping drive and 40 volts. If you have a 10 TPI leadscrew you can do the math and come up with 50 to 60 ipm. There will be screams of protest but the RPM number I use is based on reliable operation (no lost steps, no motor stalls) and based on dozens of builds and hundreds of installs. The Acceleration being too high can cause a premature motor stall. 10 is not outrageous but may be too much for your setup.

The bottom line is the faster you spin a stepper motor the less torque you have. It a non-linear curve and drops off more rapidly at higher RPM. A motors RPM characteristics (torque dropoff curve VS RPM) are dependant on several factors (higher impedance motors tend to drop off faster even though they have the same low RPM torque).

The speed of a motor then becomes related more directly to the appled voltage. The current predicts the torque (and changes the torque curve mentioned above).

Just getting bigger motors may not yield a lot more speed because the RPM's won't be much more at the same voltage. You will get better low end performance and possible move the stall point up the curve some but not enough to double the speeds.


It's ususally not and issue with pulse frequency as long as you have MACH, EMC or an external pulse gen. At 25,000 pps and 10X microstepping you can get easily get 750 RPM (if your motor will give you that). Up it to 35,000 and have pulses to spare.


If you want more speed you have to get it down at motor RPMs' where the required torque is greater. That means a lower TPI count (like a 2 start thread) or a step up belt ratio or more volts to the motors (if your drives will handle it).

In a design you balance Speed VS torque and resolution. You have to pick one or the other with steppers. A lot of router builds are using 2 start (effective 5 TPI) or even 5 start leadscrews (effective 2 TPI) and larger motors to get rapids of 300 IPM or more and still have good torque and resolution at normal cut speeds for wood and light metals.

Dual drive gantries (motor on each side) gives you double the torque where you need it the most and eliminates mechanical loses from driving both sides with one motor.

TOM caudle
www.CandCNC.com

[Drools]

Just an update, I have drilled and mounted 3 hockey pucks.
How should I test? Is there a set procedure for doing this?


I also have 8 of these transformers along with one of these MB251 bridge rectifier. and a 10Kuf@70VDC cap. I should be able to make a decent power supply if I were to connect the output of 2 transformers in series.

[Crevice Reamer]

Just an update, I have drilled and mounted 3 hockey pucks.
How should I test? Is there a set procedure for doing this?


I also have 8 of these transformers along with one of these MB251 bridge rectifier. and a 10Kuf@70VDC cap. I should be able to make a decent power supply if I were to connect the output of 2 transformers in series.

Run each axis at a progressively faster IPM until it stalls. Back off a little for reliability and see if this IPM is higher than WITHOUT the HPDs.

Those 2 transformers in series, after full wave rectification, should produce about 40V. Can your driver handle that?

CR.

[Drools]

40VDC would be fine.



- Open Source - The schematic, parts list, and software are all freely downloadable!
- Hobbyist-friendly - No surface mount parts means allows this drive to be easily repaired!
- DMOS driver chips rated at 55V and 3 Amps.
- Easy parts availability - Electronic parts are all available at Digikey. Just add your own - heat sink and mounting hardware.
- DIP Switch selectable modes of stepping:
1. Full Step, Both Phases On
2. Full Step, Wave Drive
3. Half Step
4. Quarter Step
5. Sixth Step
6. Eighth Step
7. Tenth Step
8. Twelfth Step
9. Sixteenth Step (available on special request in place of Twelfth Step mode with a special version of firmware)
- Optically isolated step, direction, & enable signals. These signals are ground referenced so no +5VDC is required - hook directly to your parallel port.
- Selectable automatic idle current reduction to reduce motor heating. Motor current can be reduced if no steps are received for 3 seconds. Oscilloscope Image, 202 kb
- DIP switch selectable motor test mode.
Allows for testing of motor/drive/wiring without an externally generated step signal.
- Motor braking can be activated when drive is disabled.
Alternatively, motor braking can also be disabled such that the motor will freewheel when drive is disabled.
- Motor current is adjustable by two potentiometers. (One for each motor phase)
Fixed resistors may be substituted in place of the potentiometers for cost savings or increased reliability.
- Removable screw terminals for all wiring connections.
- Status LED flashes during normal operation to let the user know the microcontroller is running.
Illuminates solid during a fault condition.
- Quality double-sided printed circuit board with ground plane and silkscreen legend.
Board size is 3.25" x 4.30" with mounting holes for #6 screws in each corner.