Thread: Easy Servo Drive?
I think part of the matter is my gantry is super heavy. It's probably good for cutting metal but I mostly cut wood and want fast feeds. Actually fast feeds are not a problem, it's fast changes in direction that get it confused, like zig-zag ramping on a tiny detailed pocket.
I'd probably build a whole new machine to go along with the servo motors, it it will not be the only thing I do to try and improve matters.
Last edited by Tenson; 13-09-2015 at 10:43 PM.
The way I do circular pockets is to enter with spiral entry to full depth then interpolate outwards with small stepover. There are no Centre direction changes, at the finish the tool retracts straight up or arcs out if programmed to do so.
Thou It's more likely you have the accleration set to high. Or like often the case both velocity and Accel set too high.
How much does the gantry weigh.? Do you have any pics of the machine.
What drives and how much voltage are you running them with.?
Last edited by JAZZCNC; 13-09-2015 at 10:58 PM.
I should point out I mostly use 3mm dia. cutters so this means my direction changes need to be more frequent and smaller. Maybe I'll make a video tomorrow and show you.
Gantry weight I dunno but the whole back is a massive slab of Ali. I guess 60kg.
Again same would kind of happen with closed loop.? The difference being they would or could depending on how much error fault because would still be loosing position due to being overtuned and following error will be reached.
Also what are you using to provide the pulses.? If parallel port then this could also be some of the problem.
The secret to a sound relaible machine is balance and each component needs to match and work nice together with others in the system. One weak link and the machine will be compromised in some way.!!
Last edited by JAZZCNC; 14-09-2015 at 11:36 AM.
Thanks for your replies.
Yes I am using the parallel port of a Sony Vaio Pentium 4 laptop. One thing I notice is that I get an occasional delay when jogging if the wi-fi is active. So I disable it when running.
Motors are 4nm nema 24. One pair for the main gantry (y axis) is driven from 80V and the x axis and z axis are driven from 50V. I thought the lighter weight would need less voltage but I think I probably made a mistake there as I suspect voltage directly affects motor top speed, while current affects torque? In which case my x axis will not be able to reach such a high RPM as the Y axis even though it has less weight to move.
I made a video just now. I must admit there are no problems with it in this case, lol! But I think it shows my point that the direction changes are fast at the center of the circle. This was at 2000mm/min. Circles do seem less round at higher speed and more round at lower speed. In this project I need to cut some 6mm holes and use a 3mm cutter, so the gantry will need to make very small adjustments and fast if the feedrate is high.
Anyway here it is, be gentle!
My Gantry is much heavier than yours and I can cut what you where doing twice has fast you where and still not loose position.
I'm 99% sure your problem is coming from the Laptop and parallel port. For starters Mach3 doesn't suppport Laptop with PP for this very reason of it being unreliable with the pulses coming out of it.
If you where running an external Motion controller you wouldn't be having this problem. To be honest at this speed you probably wouldn't with the PP on a decent PC with good PP. But you certainly won't with External Controller. And you'd still be able to use the Laptop.
I'll lend you a USB Smooth stepper if you want to try one.! . . . . Fry it and you bought it thou.
If your going to buy one then buy Ethernet not USB.
I think that one should use a dedicated PC (I do so) for the motion controller - turned off all visual candy staff, no anti virus, no active power saving and screen saver. In two words - everything which might take processing power or interfere with the time critical pulse generation is turned off. Using Win XP, Mach3 special driver is written for it primarily.
Laptops have built into their hardware means to save power, CPU throttling and so on. On top of that if the CPU (Intel processors) heats to a near critical temperature it has an internal protection by skipping clock cycles to cool themselves down. Had a problem with this and took me a lot of time until I discovered that the CPU cooler has detached from the holder on one side and the CPU was getting hot.
Jazz Thanks so much for the kind offer! Can you link to something that explains what an external motion controller does differently than my current parallel port to break-out-board setup? Looking at the smooth stepper site it basically looks like a USB to parallel port but I assume it must be more than that because such a thing is very cheap and small. Would I still use my break-out-board?
If it means anything I get a 'Time In Int.' on Mach3 sitting at about 4 when idle and jumping between 4 and 11 when running. Does that occasional jump mean something bad?
DeagonFly, the laptop is dedicated to CNC and runs WinXP. I chose it because it has a built in parallel port which I assumed would be better than a USB or PCMCIA adaptor.
External Motion controller is a essentially a High spec pulse engine. Basicly it's a parallel port on Super steriods. It just goes between the PC or Laptop and the BOB. You still need the BOB to distribute the signals/wires etc. It just replaces the Parallel port and takes it completly out of the equation.
In practice What it actually does is far more than just replace the PP. It takes all the Hard work of number crunching away from Mach3 just leaving mach to deal with basic tasks and house keeping. So reduces the PC and Mach3's overhead on it. This is why a Lower spec PC or Laptop can be used with External controller without any troubles.
But there's even more to it than that.!! . . .The quality of the pulses are much much higher and clearer. Also the frequency can be set much higher if higher speed are required.
These two factors are what strangle the PP and why you get missed steps when pushing the machine hard like you have been doing. Just fitting an external Motion controller will see you increase performance by minimum 25% and reliablity will be much higher. I've fitted them and seen machines gain 75% in performance using the same drives and voltage.
Connect a Good Motion controller to Good Digital drives and you'll have no troubles with lost steps and with serious performance. Yes over tune and it will like any system but you will be able to tune much higher before being overtuned.!!
Oh and you get 3x Parallel ports worth of I/O for the price.!!
I won't fit anything but Ethernet Motion controllers. To be honest I try to use Cslabs Motion controllers when ever price always has nothing out there touches them for performance to what you get but they are not the cheapest. And the lower Spec isn't ideal for machines with Slave Motors because it doesn't fully support individual switch homing yet.
Think of a Motion controller like a VERY high end Graphics Card and the PP like the Most crappest basic Card on the market.!! The difference is night and day and easy to see and hear.!
Last edited by JAZZCNC; 14-09-2015 at 04:32 PM.
By Jonathan in forum Electronic Project BuildingReplies: 17Last Post: 05-04-2015, 06:58 PM
By deisel in forum Items On eBay UKReplies: 0Last Post: 29-01-2015, 07:55 AM
FOR SALE: 160v dc servo driveBy deisel in forum Items For SaleReplies: 0Last Post: 27-01-2015, 02:16 PM
By george uk in forum Motor Drivers & ControllersReplies: 20Last Post: 23-06-2014, 07:38 PM
By Tomnewry in forum Motor Drivers & ControllersReplies: 15Last Post: 27-03-2013, 10:30 PM