Thread: Web Goblin cnc has begun
ITS ALIVE and moving!
I have finished the wiring and connected up the drives and limits.
The panel is a bit crowded but its what I had around and I didnt really want to spend £100 on a new one.
Those drivers generate quite a bit of heat so looks like I will have to install a couple of cooling fans.
I had a bit of a problem getting the pc to talk to the CPU4 control card but this was down to the pc and is sorted now. I have roughly set up the limits and Homed the machine in manual and can jog it around now. One problem I did find was when I tried to home all axes at once the machine homed X,Y and Z ok then tried to go find the A axis which is currently set to Slave X axis. I think I need to edit the Home all macro to fix this though. ( might have to pick Adcnc's brains a bit more)
The Y axis drive belt is sliding off the pulley as well so it needs a bit of fine tuning.
Linking the drivers should be ok as long as the supply cables can carry the load current without heating up. As long as they stay cool the volt drop should be minimal. I will check the full load drawn from the supply when I remember to get my current clamp meter out.
Did you have a look at the link I pm,ed to you?
I did look at the link - it's a good link thanks!
What diameter cable did you use to the drivers?
It says in the driver manual:
'For better heat dissipation, two drivers shall be installed at a clearance of at least 50mm'
With sufficient fans I'm sure you'll be fine though.
Let the resistance of a single piece of wire connecting the drivers be R. Let the current to each driver be the same, call it I. Assume it's steady state, which it's nowhere near so pretty poor assumption...Also assume no impedances other than the wire resistance ... again we should really include it but there's not really enough information to make it worthwhile so I didn't bother.
1st driver gets the supply voltage, V.
2nd driver: V-2*3IR = V-6I
3rd driver: V-2*3IR-2*2IR = V-10IR
4th driver: V-2*3IR-2*2IR-2*IR = V-12IR
So as you can see the last driver is in trouble if I and R are significant. The good thing with your drivers is they're at mains voltage, so I is not very high (maybe an amp, could peak at more) and R is (assuming 1.25mm^2 wire) about 14mOhm. That means you're loosing about 0.2V to the last driver. Compared to the 240V that's not much, but maybe when the currents are changing quickly it could be a problem as then the impedances I ignored would have an effect ... and all the drivers will be drawing different currents.
If you have 50V drivers then a reasonable average current might be 4 amps. Lets say you used the same wire, that's 50-12*4*0.014=49.3V
The thing is that DC voltage will now fluctuate, there's now about 1% ripple on the power supply. This could cause a problem if the smoothing capacitors are not big enough in the driver.
As m_c said, there's more to it than just the voltages.
(On reflection I guess working out the above didn't achieve much, but I thought it was interesting!)
Supply cables are 1.5mm^2. I dont have my regs book handy but they should be good for around 16Amps. All cables are shielded are are grounded at one end only should interference should be minimal. I will check the load drawn and the voltage supply to the last driver and see what they are. If there is a problem it will be simple to change it. I remember the manual saying about the clearance distances between drivers but the panel was already there and begging to be used. A couple of 80mm diameter cooling fans should take care of the heat.
I had managed to sort out the homing problem with the A axis by modifiying the macro.cnc file in USBCNC but I am still having loads of problems with the homing procedure. I home the machine when it is turned on and get messages saying that the homing is complete and that the home switches now act as estops which is what it should do. When I try to run a job I keep getting a message telling me to home the machine first. The only way I can get round this is to turn off the "homing is mandatory" option in settings. I had the machine setup with a slave x axis using axis a for the slave and tried Adcnc's suggestion of splitting the the x axis signal to both amps but this still had the same result. I can only think that there might be a problem in the software but not really sure about this. I am going to try another couple of modifications to the drives to see if I can get this homing procedure to work properly but if not it will stay off for good. I have also managed to get my hands on an old Lincoln welding torch cooler unit which I am modifying to use as my router cooler. Its a nice compact unit so hopefully it will work well. I need to get some more photos posted as well.
Again I have not had much time on my build lately but I have managed to get afew things done. My workshop pc died a couple of weeks ago but I have now managed to get another one up and running. I have had the machine moving about with it again. I have started to get some work done on the spindle wiring.
I need to get this finished and get the interlock from my cooler done as well before I try to run it.
I had also been looking at a way to protect the linear rails from cuttings so this is what I came up with.
Nice and simple idea. The perspex should keep the worst of the cuttings away from the rail and it will also let me see if anything gets in there.
BUILD LOG: It's begun....By Washout in forum DIY Router Build LogsReplies: 158Last Post: 07-06-2015, 09:03 AM