PR Ugrading Help With Gears and Motors

[rb99]

I have not found all my emails and notes from a few years ago. I had purchased 3 25 tooth gears, and 1 20 tooth gear.

My motors are:
3 x PK296A1A-SG 7.2 DC 1.5A 2.2 Ohms .25` step

3 x PK296A1A-SG 3.6 DC 1.5A 2.2 Ohms .5` step

I understand they are not ideal. But they what I have for now.
I also have the original small Z motor, but it won't really help here I don't think.

Which should I have for the X and Y and Z?

Thanks

[rb99]

I am going for accuracy more than speed...

Why does the Z use 20 tooth pinion and not 25 like the other axis? Does less teeth mean more speed and less accuracy?

Edit: I think less teeth = more accuracy...

[Brady Watson]

Run the .5 step on XY with 25T pinions; .25 step on Z with 20T pinions.

This is the same config as a stock PRT 3G with heavy spindle on Z (like 5hp Colombo).


-B

[rb99]

Thanks Brady.

What would be the result if I did it the other way around? Would I get much better X and Y results and then find a motor for the Z?

[Brady Watson]

It is a toss up in terms of ultimate resolution, due to the backlash inherent with the Straight Geared motors. This is why SB went to Taper Hobbed gear motors on later PRTs and all new Standard machines.

The 7.2s will give you 2X the power and resolution (on paper because of backlash) and 1/2 the speed of 3.6s. It depends how beat the used motors are when it comes to addressing backlash. They all have them...even brand new ones.

If running a PR or PRT 3G control box, top speed will probably be around 2-2.5 IPS max. If running 4G controls, it is possible to go 5 or 6 IPS. The older control boxes don't have the ability to throw steps fast enough to the motors to make them go any faster & DB9 serial is also too slow.

You can run any combination of motors on that tool, but I would lean towards putting 7.2s all the way around. I think they are only around $250 each brand new. I'd put that one on the Z.


-B

[rb99]

It is a toss up in terms of ultimate resolution, due to the backlash inherent with the Straight Geared motors. This is why SB went to Taper Hobbed gear motors on later PRTs and all new Standard machines.

The 7.2s will give you 2X the power and resolution (on paper because of backlash) and 1/2 the speed of 3.6s. It depends how beat the used motors are when it comes to addressing backlash. They all have them...even brand new ones.

If running a PR or PRT 3G control box, top speed will probably be around 2-2.5 IPS max. If running 4G controls, it is possible to go 5 or 6 IPS. The older control boxes don't have the ability to throw steps fast enough to the motors to make them go any faster & DB9 serial is also too slow.

You can run any combination of motors on that tool, but I would lean towards putting 7.2s all the way around. I think they are only around $250 each brand new. I'd put that one on the Z.


-B





I am switching the motors to have the 3.6 on the X and Y, with the 7.2 on the Z. I phoned SB and this is what they recommended. They said the 4G controller does not work well with the 7.2 as they won't get enough power. Do you agree?

[Brady Watson]

What does the motor plate of each show for amps?

-B

[rb99]

What does the motor plate of each show for amps?

-B


They show 1.5 amps

[Brady Watson]

Then both motors make the same amount of power. Amps = power/torque. Voltage = speed/RPM.

Since the 7.2s have 2X the mechanical reduction as the 3.6s, it will have 2X the torque, but 1/2 the top speed. Both "motors" are identical. The gearboxes are different.

A 'hot' power supply, like the 63v toroid supplies in the newer 4G boxes will push the power band up and give you some more top speed - IF your COM speeds are fast enough to take advantage of it.

I put a 4x4 PRT together with 7.2s all the way around & it was fantastic. I realized I didn't need all the torque and wanted a little more speed so I upped the 25T to 30T and it actually cut more smoothly (with more teeth engaged in the rack @ the pinion), plus longer pinion life. The motors I had were TH series, so the SG might exhibit a bit more backlash - but other than this, it should be pretty sweet. It's fine with the 25T though...

Conversely, the 3.6s will move faster, but you really don't want speed on a PR. It just can't handle it. Torque + resolution = smooth stable machining & cut quality. Try it...worst case you put the 3.6s on - but I think you will really like the 7.2s if the gearboxes aren't too beat.

When you run UR to setup a config file for the 1st time, it will be for 3.6 motors. Double all the UV values if running 7.2s AND 25T XY and 20T Z pinion...or things will only move 1/2 as far as they should. E.G. - PRT 4G Z axis @ 2291.831 with 3.6 motor, but 4583.662 with 7.2 motor.

-B

[rb99]

Thanks Brady. It is really good to have your experience on this.

Do you think I would be OK with a 3.6 20 tooth on the Z?

[Brady Watson]

You're welcome. It will be fine on the Z, but 7.2 would be better for intricate 3D stuff because you will have more resolution and torque. Try it...If you need more, snag another 7.2 for the Z. All PRTs had the 3.6 on the Z unless you ordered a heavy spindle.

-B