Servo reduction Ratio and belt recommendation

[liquidcooled]

So I’m in the process of rebuilding a plasmacam 98z I got for cheap. Redoing the electronics for a number of reasons.

Everything is going good is far and electronics wise I’m doing well and have all the limits and z axis rocking and rolling. And can spin the z axis motor up and down no issues. Have the other two motors arriving in a couple days.

Not real happy driving the old plasmacam motorson there though. They work just real slow when running off the gecko drives and the belt system was really bad on these. It was a 5/16 40 D.P. belts on the original machine for the record.

The original setup on both of the x and y axis are a pulley that has a diameter of .40” (roughly)

The y axis has the be,t from the motor run to a 3” pulley. This 3” pulley attaches to a cross shaft that runs to rack on both sides. This should roughly yield a ratio of 7.5:1 reduction. The pinion on this cross shaft is 1.45” at the root of the cut.

The X axis Has the belt driving a 1.5” pulley. This should give a ratio of 3.75:1. That then drives a pinion on gear rack. The pinion is .7” at the root of the groove.

Motors I’m I’m planning using are Nema 23 servos since the gantry isnt really heavy on this.

Specs: 4700 rpm max, 50 oz constant torque, 350 oz peak torque.

Running gecko 320x with amt 102 encoders.

https://www.automationtechnologiesinc.c ... .php?id=76

So questions I have ?

1. What pulley ratio should I be shooting for for in order to drive the x and y axis at a fast enough speed for proper cutting? How do I calculate inches per minute?

2. What is everyone running for encoder resolution settings?

3. As far as belts go is there an advantage to going with a gates rounded gt2/gt3 shape engagement vs a trapezoidal one?

3. Will a 3/8 ish size belt be of sufficient size to keep from braking or do I need to go to a 1/2” class belt. The 3/8 size stuff is much much easier to find.

Thanks,
Mike

[tcaudle]

do some math. First look at the motor volts versus what you can supply. Top RPM is only at full rated voltage. Its proporional. Then look atthe diameter of the pinion gear . Multiply by PI to get the circumference. That gives you the rotation ratio (how far it rolls per revolution. THEN take te max rpm of the motor at the voltage you are using (gecko only does 80 V max which is why the PCAM motors run so slow beacause they are high voltage DC motors (160VDC I think) and RPM is proportional to the voltage. Getting much reduction with toothed belts is going to be hard. About 5:1 is about all you can expect . So you take the top RPM of the motor and multiply it by the circumference of the gear and that gives you linear IPM if it were direct drive . Then you divided it by the ratio to get final top speed. There is a balance between speed and torque. You want as much torque as you can get while having reasonable speeds for rapids. The motors you describe soundl like the 23 frame 72 volt ones with 50 OZ-in . It pretty easy to stall those so you need torque gain for acceleration. You get more torque with a higher ratio belt reduction . Play with the numbers but be mindful that those G230X drivers will supply up to 20A at 80 VDC and if you stall one of thes small servos (lock the shaft) you can count to about 20 before the motor gets so hot it burns out. Set your torque control way down so it limits to about 5 A .