It's an option. If you go into General config there's a setting called Home SW safety. Tick this and it will enable limits while homing. Obviously if sharing the same switch as limits this needs to be off.Quote:
Originally Posted by cropwell
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It's an option. If you go into General config there's a setting called Home SW safety. Tick this and it will enable limits while homing. Obviously if sharing the same switch as limits this needs to be off.Quote:
Originally Posted by cropwell
And do you think you'll need more than 10 inputs and 24 outputs.? I'm also not sure if some of those Outputs on the second port can be configured as inputs in software.? Only if you plan on having an ATC will you probably need more than 10 inputs.Quote:
Originally Posted by dazp1976
Regards the Cheap BOB then yes, of course, it will make a difference. It's like having 500HP engine and fitting bald tyres.? Pointless.!
Any machines only as good as the weakest link so fitting a good card with a cheap BOB that probably can't keep up doesn't make sense to me. This whole thread proves this.
I fit good electronics, which yes cost more, but I never have any of this shit to deal with and the extra cost is made back by the fact I'm not running around fixing machines or put another way the owner doesn't have any downtime which costs money.!! . . . . You get what you pay for.!
If your going to use a cheap BOB then save your money don't buy ESS or ETH400 and use Linux CNC. You have half a chance of good machine and won't cost anything other than it's a steep learning curve.
What gobsmacked me the most was the amount of noise before I ever put mains on to the VFD. It's enabling the motors that introduces all the trouble. And the fact that the same noise is on the ground of the BOB. I thought the screening and earthing was quite reasonable but noooooo!Quote:
Originally Posted by Doddy
One thing that all this does point out is how noise-resistant it is to use NC microswitches on the limits. Under normal operation all the limit inputs have a hard-wired, all metal connection short circuit on them. This is why I've never had any of this trouble before. Ironically I did briefly consider using miniature relays to act as the 12 or 24V to 5V interface but considered it unprofessional and was in fear of being laughed at by my forum fellows. Actually it would work a treat! I doubt if the variation in triggering delay would noticeably affect the accuracy of the homing and the low-pass filtering effect would be even better than your suggested opto-couplers!
Re the 'experience', which isn't really as great as you so kindly implied: When I was a trainee at the BBC, back when Boris Johnson had a poster of Prime Minister Thatcher on his school dormitory wall, one of the trainers gave a demonstration of how there's no such thing as an earth connection at radio frequencies. This was at the Daventry short wave station which is now long gone. We went out into the antenna field and he took a coin out of his pocket and dragged it at head height down the side of a steel support post which carried one of the feeders to an antenna. This post was about 20cm or so in diameter and solidly concreted into the ground. There were distinct, bright sparks between the coin and the post!
Dean,
For a commercial machine that has to earn it's keep I'm in complete agreement with you. I'd have gone bankrupt a long time ago if I were mad enough to try and use the machine I've built as part of a business. But for me it's just a toy I have in my shed and I can't justify spending large amounts of money on it for new parts I can probably do without if I apply some time and ingenuity to the problems that arise. With the $AUD currently worth no more than about 60 US cents, prices of most other board options are way too high.
In practice this $20 BOB has done everything I need from it for several years now and the current noise problem is nothing to do with the board itself. I'm actually quite impressed that it worked so reliably before, with NC microswitches to hide the problem, and has proved quite robust as well, not complaining at all when I accidentally put 12V on one of the 5V limit inputs.
Building and modifying the machine and learning from the problems that occur is part of the fun of making it for me, it's hobby in itself, though there is an ever-increasing list of other projects on hold that are waiting for it to be working properly again.
That doesn't really suprise me - I remember when I powered up my first PWM audio amplifier - which was switching roughly the same voltage and frequency as a decent microstepping drive - and the radio in the workshop promptly went off. Holding a 'scope probe 6" above the speaker leads gave a few volts of noise in thin air, I ended up using screened speaker cable :listening_headphone:. Are the cables to your motors screened I wonder? As with the sensors when I extended my cables I cut them very short then extended with screened (2 pair) which might explain why I've not had any problems in a setup which seems somewhat similar to yours - I'm using basically the same type of sensor albeit in the M8 size. The motor cable screens I returned to the HT- pins on the drivers (always return your shit to where it's generated!) which then has a VERY SHORT ground lead down to the aluminium back plate of the enclosure which acts as a ground plane - being an RF man you'll appreciate the benefits of those.Quote:
Originally Posted by Kitwn
Voicecoil,
I thought I'd been quite careful with the wiring: the BOB is in it's own aluminium box, the outputs to the drivers are 4 core screened, the cables from the drivers to the motors are screened, the PSU for the BOB (it's the original ATX supply in the PC case that is my control box) is a separate unit from the motor PSUs, the VFD is separately mounted on the wall, the spindle power cable is proper screened cable designed for the job.
The weak point is the sensor wiring which was not all screened cable for the old microswitches and has not been totally replaced yet, but will be soon. All the grounding of every component in the control box will need to be looked at again as well. No going down to the pub this evening for me!
Simon,Quote:
Originally Posted by Cube3
Apologies for not getting back to you earlier, I got somewhat sidetracked away from the original reason for this thread.
That's a very interesting video and I especially like the improvised current transformer for investigating noise, I hadn't seen that trick before but it will be useful in future. As I've discovered the VFD is not to blame (yet!), it's enabling the motors that generates the noise I'm investigating at the moment. Once that's been quietened down I can then see if the VFD adds any problems. It wasn't an issue when I had NC microswitches for limit sensors so my fingers are crossed on that one.
Well, you've done a thorough job then, strange that you're seeing so much induced noise - unless it's induced pickup of magnetic field radiation?. It will be interesting to see what you come up with as a fix.Quote:
Originally Posted by Kitwn
Hadn't considered magnetic induction, probably not the cause at such a high frequency, but I'm willing to be proved wrong. It wouldn't be the first time!Quote:
Originally Posted by Voicecoil
I've still got some investigation I want to do. The controller is connected to the machine by screened multicore cables which have plugs on the end which fit into sockets on the machine itself. The two X axis sensors and the Z&Y sensors have one 8-way for each pair. I want to disconnect the cables and see if that makes a difference. This will help to decide if the noise is being picked up in the wiring within the machine itself where the Z and Y sensor cables run through the same drag chain as the motor wiring or whether the problem is within the controller itself. Both will be dealt with anyway but knowledge is never wasted. I'm also tempted to use the technique I learned from the video that Cube3 linked to to look at the noise on the motor cables with my laptop oscilloscope. But 6MHz???
While I wait for RS to deliver the bits required I'm doing some necessary tidying up. There isn't much room in my workshop with the machine itself pulled off the wall to get at all the wiring (note for new builders: If you have to put your machine up against a wall, do NOT put the drag chains and all the gantry wiring on the 'wall' side of the machine in order to keep it conveniently out of the way). The only place to put the trolley with the PC on is in the doorway to the rest of the shed (sorry, that should be 'studio' if my wife is listening) if I want to leave it all connected so the picture below had to be taken through the window!
Attachment 27733
The weirdest things can happen with EMC issues, at 6Mz a couple of bits of wire running parallel for a few m probably makes a half decent transformer :teapot:Quote:
Originally Posted by Kitwn
No chance of that for me either - 'coz of the virus they've been shut here for over 2 weeks :dejection:Quote:
Originally Posted by Kitwn