[Grascochon]

Hi folks, I'm new here. I've been through the forums a lot and feel that I already know you guys
As a beginner as well as not being the sharpest cutter in the shop, I was trying to research as much as possible before posting obnoxious questions all over the place. But now I think it's time to bother the cnc wizards a little with my broken English. I posted this at the acorn forum, but since there is a lot of experts on this forum, I thought I'd try here as well. There are threads for this kind of stuff, but it's old or for other hardware.

To the point:

I'm trying to set up a freshly arrived Taig mill and a taig lathe (ballscrews).
I went for acorns, dyn2 drivers and dmm 57n-dht motors (was this a good choice?)

I've searched all over and watched the precious Martyscncgarage videos and got to the conclusion that I should use the 2000/8000 pulse settings for Gear_num and pulse count on the Acorn.

Then I came across this bit of text somewhere on a forum (forgot where, sorry):

Electronic gear reduction parameter. GEAR_NUM x 4 = number of pulses needed to rotate motor 1 revolution. For example, if GEAR_NUM is set to 1,000, then 4,000 pulses are needed to rotate motor 1 revolution.

Generally, GEAR_NUM should be set as high as possible for best resolution and smoothness. But GEAR_NUM also affects max motor speed depending on CNC controller pulse frequency so this should be balanced with the speed requirement:

Example 1: Controller max pulse frequency = 100kHz.

Machine target speed = 500IPM.

Motor direct drive on 5mm pitch ball screw.

500inch/min / 5mm/rev = 2540rev/min from motor.

2540rpm = 42.33rev/second.

100kHz = 100,000pulse/sec / 42.33rev/sec = 2362pulse/rev.

So set GEAR_NUM to 590.

Note 1. The GEAR_NUM parameter is only used to calculate the command from the CNC controller. The servo drive and servo motor always maintains position at 16-bit (65,536points/rev) resolution

Note 2. GEAR_NUM setting should allow at least twice the resolution of machine accuracy target. See example 2 below.


Example 2. If motor is driving a rack and pinion axis with a 2:1 reduction and 25mm pinion diameter. Target accuracy = 0.05mm. 25mm diameter pinion = 157mm circumference (linear travel per pinion revolution). 157/2 = 78.5mm linear travel per motor revolution. Twice target accuracy = 0.025mm. 78.5/0.025=3,140points/rev. So set GEAR_NUM to at least 785.

The LINE_NUM is the same as the GEAR_NUM but it controls the resolution of the encoder OUTPUT. The GEAR_NUM is the pulse ratio of the pulse/dir command input from the controller. The LINE_NUM is the encoder output resolution from JP5 connector. The MASSO doesn't read the encoder from the drive so this parameter is not used.

Servo direction, if a servo rotation needs to be reversed (as in a slave situation), the Dir+, and Dir- can be reversed on one of the drives without damage. The Masso also has an option to do this in the Slave axis window.

So from that I thought I would calculate the best settings for my ballscrew taig, dmm 57n and acorn. And I came up with this:

My taig has 2.5mm pitch diameter ball screw, I want to target a rapid speed of 100 ipm on the Taigs.

2.5mm = 0.0984252 inch pitch = 10.16 rpi (rotation per inch)

rpi x steps = spi (steps per inch on driver)/4= steps per inch on acorn

What ipm max speed can dmm 57n motor take (rated at 3000rpm)?



3000 rpm / 10.16 rpi = 295 ipm (motors rated at 3000 rpm)

I need 100 ipm

100 ipm x 10.16 rpi = 1016 rpm (lots of head room to 295 ipm)



So the motors can take 100 ipm (our target) easy = 1016 rpm (torque is consistent up to 3000rpm)

What maximum steps per seconds can Acorn controller do?

MAX frequency is 400 kHz (you have to set this in the wizard, default is 200khz) so that means 400000 steps per seconds

(the pmw can’t be shorter than 0.8us on dyn2 driver, and from what I understand acorn will give us just a bit over 1us pmw at 400khz)


What steps per seconds do I need at 100ipm (1016rpm)?

1016 rpm = 16.93 rps (rotation per seconds)

16.93 rps x steps = sps (steps per second)

controller 400’000 sps (capable) / 16.93 rps = 23626 steps per rotation are available

motor max steps per rotation is 65’536 (16 bits encoder) but we are allowed only 23’626 from acorn at a speed of 100ipm.

the motor has 2.73 times more res than acorn is capable of.
That's why I can't use the full 65'536 the motor encoder could take.



To be safe, I'll set my encoder settings (pulse per rotation) in acorn at 20480 steps per rotation

on the dmm dyn2 driver (GEAR_NUM x 4) it will be /4 = 5120

and our rpi is 10.16

For more headroom but less precision I could go 4096 and 16384



Does this look correct? or do you see obvious mistakes?
I'm gonna try this and see how it goes, but I'd be happy to see what you guys think about this to help me troubleshoot.
I've read somewhere that when people go over 2000/8000 they get problems even though it should work.

Thanks and Cheers.

[mactec54]

Hi folks, I'm new here. I've been through the forums a lot and feel that I already know you guys
As a beginner as well as not being the sharpest cutter in the shop, I was trying to research as much as possible before posting obnoxious questions all over the place. But now I think it's time to bother the cnc wizards a little with my broken English. I posted this at the acorn forum, but since there is a lot of experts on this forum, I thought I'd try here as well. There are threads for this kind of stuff, but it's old or for other hardware.

To the point:

I'm trying to set up a freshly arrived Taig mill and a taig lathe (ballscrews).
I went for acorns, dyn2 drivers and dmm 57n-dht motors (was this a good choice?)

I've searched all over and watched the precious Martyscncgarage videos and got to the conclusion that I should use the 2000/8000 pulse settings for Gear_num and pulse count on the Acorn.

Then I came across this bit of text somewhere on a forum (forgot where, sorry):




So from that I thought I would calculate the best settings for my ballscrew taig, dmm 57n and acorn. And I came up with this:

My taig has 2.5mm pitch diameter ball screw, I want to target a rapid speed of 100 ipm on the Taigs.

2.5mm = 0.0984252 inch pitch = 10.16 rpi (rotation per inch)

rpi x steps = spi (steps per inch on driver)/4= steps per inch on acorn

What ipm max speed can dmm 57n motor take (rated at 3000rpm)?



3000 rpm / 10.16 rpi = 295 ipm (motors rated at 3000 rpm)

I need 100 ipm

100 ipm x 10.16 rpi = 1016 rpm (lots of head room to 295 ipm)



So the motors can take 100 ipm (our target) easy = 1016 rpm (torque is consistent up to 3000rpm)

What maximum steps per seconds can Acorn controller do?

MAX frequency is 400 kHz (you have to set this in the wizard, default is 200khz) so that means 400000 steps per seconds

(the pmw can’t be shorter than 0.8us on dyn2 driver, and from what I understand acorn will give us just a bit over 1us pmw at 400khz)


What steps per seconds do I need at 100ipm (1016rpm)?

1016 rpm = 16.93 rps (rotation per seconds)

16.93 rps x steps = sps (steps per second)

controller 400’000 sps (capable) / 16.93 rps = 23626 steps per rotation are available

motor max steps per rotation is 65’536 (16 bits encoder) but we are allowed only 23’626 from acorn at a speed of 100ipm.

the motor has 2.73 times more res than acorn is capable of.
That's why I can't use the full 65'536 the motor encoder could take.



To be safe, I'll set my encoder settings (pulse per rotation) in acorn at 20480 steps per rotation

on the dmm dyn2 driver (GEAR_NUM x 4) it will be /4 = 5120

and our rpi is 10.16

For more headroom but less precision I could go 4096 and 16384



Does this look correct? or do you see obvious mistakes?
I'm gonna try this and see how it goes, but I'd be happy to see what you guys think about this to help me troubleshoot.
I've read somewhere that when people go over 2000/8000 they get problems even though it should work.

Thanks and Cheers.

I have not read all your post yet, but for starters you want to be using a Gear Number of 500 this is 2000 PPR start with this you will never change it to anything else for what you want to do

The Encoder Resolution has nothing to do with your set up, you can't change the Resolution it will always be 65,536 PPR the accuracy does not change with the Gearing

So set the Gear to 500 and forget it, now you know you have 2000 PPR at the motor so to set up the step/Per you need to know the Ballscrew Pitch or RPI

So I hope this is clear the Gear number does not change the Encoder Resolution this never changes 65,536 PPR

Is this a good system you have yes it is you could not get anything else close to it

[Grascochon]

Ok, thanks. That’s helpful,
But still , I ’m confused, isn’t the gear-num a rescale of the resolution?
my fancy numbers seem to work good so far, but I’ll try with a low 500/2000 to see if I can notice any difference. Probably not.
I wanted to use all the resolution I could squeeze out of the acorn and driver.

From DMM tech support:

Generally, GEAR_NUM should be set as high as possible for best resolution and smoothness. But GEAR_NUM also affects max motor speed depending on CNC controller pulse frequency so this should be balanced with the speed requirement:

[mactec54]

Ok, thanks. That’s helpful,
But still , I ’m confused, isn’t the gear-num a rescale of the resolution?
my fancy numbers seem to work good so far, but I’ll try with a low 500/2000 to see if I can notice any difference. Probably not.
I wanted to use all the resolution I could squeeze out of the acorn and driver.

From DMM tech support:

Generally, GEAR_NUM should be set as high as possible for best resolution and smoothness. But GEAR_NUM also affects max motor speed depending on CNC controller pulse frequency so this should be balanced with the speed requirement:

No the Gear number is a scale, or gear ratio from your supply control output to the drive so the acorn has anything you need for Step/Dir PPR to supply the output to the drive

You keep talking about resolution, that does not change no matter what you use as your Gearing number 500 is the smoothest as there will be more PPR required more PPR = smoothness resolution is 65,536 this does not change

You won't notice much difference on the machines you have as they are not capable of doing very heavy cuts, but you will see the jerk factor, the higher your gear number is

The Acorn has nothing to do with the resolution your Encoder is what is the resolution 65,536 PPR