Messages

171

General Mach Discussion / Re: servo motors

« on: October 24, 2014, 04:34:38 PM »

I'll sneak in and recommend Dynomotion's KFlop combined with a Kanalog, however it does involve a bit more knowledge to setup than the above options. It is however far more powerful and opens up lots more options of what can be acheived.

172

General Mach Discussion / Re: Steps/Inch on Lathe = 75,000; Seems a Tad High

« on: September 15, 2014, 05:52:36 AM »

And the Backlash_Linear is because it leaves open the option to add other backlash modes at a later date.
Linear is the simplest method to handle backlash, but there are other more complex methods.

173

General Mach Discussion / Re: Steps/Inch on Lathe = 75,000; Seems a Tad High

« on: September 15, 2014, 05:49:33 AM »

The official quote from the manual-

Sets or gets the Backlash Compensation mode from either BACKLASH_OFF (0) to BACKLASH_LINEAR (1).  When the backlash mode is set to Linear mode, whenever the commanded destination begins moving in the positive direction, a positive offset of the amount, BacklashAmount, will be applied.  The offset will be ramped upward as a linear function of time at the rate specified as the BacklashRate.  Whenever the commanded destination begins moving in the negative direction the offset will be removed by ramping downward toward zero at the same rate.

What it essentially means, is that when you move in the positive direction, the backlash amount gets added, at the rate specified by BacklashRate.
So to use some random figures, say you have backlash set at 1000, with a backlash rate of 1000.
Now you command a move of say 3000 steps at 1000 steps per second. As the axis moves at the set rate, it applies the backlash on top of the set motion rate*, so after 1 second, the axis has actually moved 2000 steps. After the backlash has been applied, the axis then continues to move at it's set motion rate of 1000 steps per second until it reaches 4000 steps, which if your backlash is set correctly should be the equivalent of moing 3000 steps.
If you then command another move in the same direction of say 1000, as backlash has already been applied, the axis simply moves 1000 steps, so the axis should of now physically of moved 4000 steps (or 5000 steps with backlash applied)

In reverse, the exact same thing happens, but things count down instead of up. So if you start at a physical 4000 steps (5000 with backlash applied), and command a move of 4000 to return to zero, as the axis starts to move, an additional 1000 steps will be added to the first second of motion to remove the backlash amount.

The idea is, that due to backlash applying no load to the drive system, it can be added quickly to motion moves, so that backlash is removed prior to the axis physically starting to move. The 1000 step example I used is very high setting for most systems, and in practical use a backlash setting that high will cause problems. Backlash is essentially a sticking plaster solution, and only really meant to handle very minimal backlash which can't be removed through other means.
Any large amounts of backlash where the tool can pull/push against the backlash, means that if you use a high backlash rate, you can miss steps due to a large amount of backlash being too quickly applied against axis load, however if you use too low a backlash rate, then the backlash won't be applied quickly enough during moves.

174

General Mach Discussion / Re: Mach3 and external motion controller

« on: September 04, 2014, 06:42:27 PM »

The issue is anything that relies on Mach3 to handle an input, is going to have a delay while buffers get emptied.

KFlop is the only interface I know of that can interupt that delay, as it can be programmed so it directly responds to an input change, and not rely on having to notify Mach an input has changed then wait for Mach to decide to do something about the change and add it to yet another buffer.

From what's been mentioned so far, Mach4 will respond far quicker, but I think it will still depend on how individual plugins are programmed.

175

General Mach Discussion / Re: Steps/Inch on Lathe = 75,000; Seems a Tad High

« on: September 04, 2014, 06:32:30 PM »

Just realised the bit I mentioned about making sure Mach isn't slowed by the KFlop settings might be causing you issues.

Take your 75000 steps per inch figure as an example.
Ignoring acceleration for now, if you command a move of 60inch per minute, you need KFlop to generate 75000 steps per second.
Now if you have the axis/channel in KFlop set at a max speed of say 50'000, that means the KFlop/actual motion is going to trail Mach's planned trajectory by an ever increasing 25'000 steps per second, or 1/3" per second.

This also applies to acceleration, but you also have the added complication of jerk.
Using the same 75'000 figure, say you have your acceleration set at 1"/sec^2, this means after 1 second Mach expects motion to be at 1"/sec, and the KFlop should be outputting 75'000 steps per second to acheive this, which you would think is acheivable by setting an acceleration rate of 75'000 in your axis/channel.
However, that doesn't allow for Jerk. If you have Jerk set to 75'000, it's going to take 1 sec for the KFlop to reach max acceleration, by which point you're lagging behind the Mach trajectory.

I can't remember how KFlop handles the lag scenario, but I suspect it just continues to buffer motion.
And having just searched the yahoo list, the axis commanded position will keep increasing while the actual position lags, to the point where either the axis disables because of max following error limit being exceeded, or if trajectory stops allowing the axis to catch up, the axis will come to an abrupt uncontrolled stop.

So the moral of the story is, make sure you're conservative with your Mach settings.

176

General Mach Discussion / Re: Steps/Inch on Lathe = 75,000; Seems a Tad High

« on: September 04, 2014, 06:01:07 PM »

It's count/sec^3, where count is either encoder counts, or microsteps depending on what you're driving.

KFlop has no interest in whether you're working in inches or mm, it's only interested in raw numbers. It's upto Mach/KmotionCNC/whatever other interface you're using to create the raw numbers via a format that humans are more likely to comprehend.

177

Show"N"Tell ( Your Machines) / Re: A Wee Prober

« on: September 02, 2014, 06:51:08 PM »

Tweakie, do I sense a hint of sarcasm in that post?
I'm not sure if there will a next installment as such, as the only things I've got planned to do now is cut a whole for the scale connectos, and put the door on the cabinet.

Dickeybird, the KFlop is a very powerful and highly configurable option.
Provided you can input a suitable signal, you can close the loop with pretty much anything a KFlop output is capable of driving.
Some combinations will require some custom C code, however most common motion control related inputs are handled easily through the standard options. I think the only main requirement for a suitable input, is it has to be quadrature.
Also, it's sampling rate is 180uS on all inputs, so even standard inputs can be used for some pretty time critical stuff.

178

General Mach Discussion / Re: Steps/Inch on Lathe = 75,000; Seems a Tad High

« on: September 02, 2014, 06:39:22 PM »

Couple things if you're using that file as is.

Remove the bit that disables the amplifiers after being idle for a period, as it means position can be lost if the steppers happen to move when power is removed.
Also when running mach, I'd remove the SetBit(45) line, and instead set an enable in mach to Port 1 Pin 45, so the amps only get enabled when Mach does.

Jerk is a measurement of how quickly acceleration/deceleration is applied, and in KFlop is a measurement of counts/pulses per second per second per second (I bet you had to read that several times, as it took me a while to get my head around it!)
Without jerk, which is how Mach3 runs, on acceleration there is a sudden increase in the rate of pulses, which leads to a sudden change in force as something stationary suddenly has to accelerate. With jerk, the rate at which the acceleration is applied is controlled, so you get a smoother start to acceleration.
Think of it as when you press the accelerator in a car, if you suddenly stamp it to the floor, you start accelerating quickly and provided you've got enough horses under the bonnet, you get abrubtly forced back into the seat.
Now taking the same car, if you gradually press the accelerator to the floor, you ultimately get to the same acceleration rate, however you don't get as abrubtly forced back into the seat.

The trick is applying enough Jerk, so things accelerate smoothly and quick enough without causing jerky movement. It does essentially result in a very basic S-curve motion profile.
One thing to note, is while running KFlop with Mach, you have to ensure that the Mach settings aren't limited by the KFlop settings, as the KFlop max speed settings will over rule Mach settings. This can lead to a condition where actual movement is ever increasingly lagging behind Mach. I'm not sure what would happen if the lag becomes too big, but it's something to be aware of.

However none of that explains your step per unit issues.
I'd maybe try dropping the acceleration rate and speed rate down in Mach, incase you're loosing steps during the moves. Another way to check for this would be to set up a dial gauge against the carriage, zero the axis, then do a rapid away, then a slower feed return to the gauge. You're most likely to lose steps during the rapid, so doing a rapid in one direction followed by a slow return is more likely to show up lost steps.
Might also be worth checking that all your couplings are tight.

My next move after that would be visually check the motors are turning the correct number of turns for a requested move. i.e. mark the motor/coupling then command a move of 0.125" and check the motor does rotate one full turn. And if it does, check your screw is 8tpi.

179

General Mach Discussion / Re: Steps/Inch on Lathe = 75,000; Seems a Tad High

« on: September 02, 2014, 02:09:44 PM »

You don't need or use the mot files. They're solely motor config files, which are only any use via the config&flash screen.All you use for most things are c files, which are what configure the motors for normal use.

180

General Mach Discussion / Re: Steps/Inch on Lathe = 75,000; Seems a Tad High

« on: September 02, 2014, 01:07:19 PM »

That's correct, however the example files are set up for 3 or 4 axis, so you'll need to change it.