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Member postings for Bob Mc

Here is a list of all the postings Bob Mc has made in our forums. Click on a thread name to jump to the thread.

Thread: Syncing up Arduinos
14/12/2015 18:28:11

Hi Jason.... another good question..!

Andy has hit the nail on the head in his response.

Basically use could have been made of a more powerful processor which would in principle have the capability of providing 2 sets of independent clock pulses from the one processor.... however and unfortunately the Arduino can't do this.

I have to admit that although I worked in electronics for many years I was not involved in programming.

I decided some time ago that it was rather pointless to start learning programming when I had so many other things to take up my time and interest.

the Arduino programming was however much simpler and the open source ideology along with the many forums and articles makes the whole thing less daunting than trying to get to grips with full blown programming.

As stated in the article... 'there are I am sure other ways of doing this' ... and I have recently been told that one of the Atmel processors is capable of providing the required pulses, but I have not pursued it.

My idea in using this system of two Ard'os just kept it simple and easy to understand although wiring up for one clock is not the easiest thing to do.

If you are really considering having a go, I would try to do the wiring of the xtal clock circuit done first and test it using the 'Blink' program ... if the two Leds keep in sync over a minute or so...you are in business...!

The other thing that didn't come out in the article very well was the fact that if there are any overall errors in the leadscrew pitch, this can be accommodated with the system and as stated my leadscrew is just a piece of threaded rod, ....will provide details if you need them.

Please remember that this is a 'model engineering project' and although I have produced a number of different threaded items such as a spindle end nut for my Atlas lathe, the spindle motor of 3.1Nm is not really capable of taking deep cuts and an amount of experimentation is needed to determine what it will actually cut, in hindsight I should have fitted the next higher power of stepper motor, something of the order of 5Nm, the drivers I mentioned are capable of powering a motor of that size.

Any more info required..... I am only too pleased to help.

rgds...Bob.

14/12/2015 16:35:53

Hi Andy... A good question...!

The reason why synchronisation of the two Arduino's is necessary is that the two motors (one drives the leadscrew and the other the Spindle), need to have their relative speeds constant, notice the term 'relative' .

For example if the required ratio of Spindle speed to Leadscrew speed was 1:4 then for 1 turn of the spindle there would be 4 turns of the leadscrew ; if the pitch of the leadscrew was 1mm then 4 turns would produce a pitch of 4mm on the work.

Now if the Arduino driving the leadscrew motor began to increase or decrease its speed relative to the Spindle motor speed, the ratio of 1:4 is altered and the required pitch on the work would no longer be 4mm.

It is an unfortunate fact that no matter how good the clock circuits are in any two microprocessor systems they will not keep in sychronisation if they are completely separate systems.

The Arduino can only provide a minimum clock pulse period of 1microsec duration, using two Arduino's the clock pulse rates will most certainly alter over time which is the root cause of the problem, and so by using only one clock for the two Arduino's the problem of clock drift is eliminated.

It might be thought that the difference in speeds would be so small that it really wouldn't amount to much, however when the work requires long pitches to be made all the errors begin to add up, If you have two Arduino's just try the Blink program with a 500ms delay period for switching the Leds on & off... it won't take long for the two Leds to be out of sync.

Hope that helps, if you need any more info I am only too glad to help.

rgds..Bob.

14/12/2015 15:23:25

Hi Andy...

I wrote the article about using Arduino's .... if you need any information just let me know on this forum.

..rgds...Bob McMenemie.

Thread: Affordable CAD software?.
13/12/2015 12:39:33

Thanks everyone for the responses...

its great to know that once you are a member of this forum there is a wealth of information from people that understand the situation and have the experience to provide a solution...

Thanks .. will be spending some time looking at your suggestions.

..Bob..

12/12/2015 19:48:06

Please let me know if this has already been discussed, however I can't find any reference in the Threads for this topic.

I would like to make a start producing drawings using some sort of CAD, however I was blown away when I saw the price of Autocad..!!

is there anything that would be suitable for model engineers and which could be used for uploading to ME magazine for example, surely there must be something reasonably priced....well less than £50 in my case or its out of my league.

Have looked on Ebay and although there are copies of what is claimed to be Autocad, it appears that they are either free trials or somewhat legally 'iffy'; in the first case I don't want drawings disappearing from my files after a certain time, and in the second case I don't want to end up in clink..!!

Thread: Screwcutting Clutch for Myford Lathes
28/03/2015 19:54:36

Re: Hi Q...

I do apologise to Neil, he has actually sent me a message on the 17th, I am new to these forums, did not realise I had an 'inbox'.

Bob.

28/03/2015 19:49:12

Hi Q....

I am in the process of writing up an article for Neil, so I can't really say much about how to construct the thing when it may become an article, and at this moment in time I still await Neil's confirmation of how long an article he would like but as yet I have not had a reply, having not done anything like this previously I do need an indication of what to do next.

I can tell you that it actually has similarities to the Myford Screwcutting clutch albeit in electronic form so it does have some bearing on the topic of this forum.

I don't think I will be saying things out of place if I say that it would be best to have a reasonable understanding of the Arduino, I only ever had Simon Monks "Programming Arduino" which is more than adequate for this project; read up on the use of the Interrrupt function, I can honestly say that the programs are so simple you don't need to be an expert.

Bob.

17/03/2015 16:14:10

Hi Neil...

I have re-posted but there is a problem with sending to the address you gave me, anyway, the answer is basically

Yes.. will try emailing again.

16/03/2015 22:59:44

Thanks Geoff, ... kind words come from a kind person.

I am hoping to do an article about the 'electrickery' device... have emailed Neil... will have to wait & see, so I can't really say too much about it at the moment.

rgds ...Bob.

15/03/2015 19:51:49

Hello Michael and All... Michael asks..."More details please!".

Its a bit of a story really,

I was given an old Atlas 10F lathe, the tailstock was missing, the leadscrew was worn out and there was no backgearing; it was to go for scrap, I thought it a shame since the bed ways were ok and so I used a piece of 20mm diameter stainless threaded rod for the leadscrew.

After successfully making a new clasp nut the lathe seemed to be performing rather well and gave me the impetus to have a go at making a slow motion drive for the leadscrew; at this point I must tell you I worked in the electronics industry for many years, and although it was easy enough to fit a motor to the leadscrew I had by then seen the Electronic Leadscrew Groups website and was considering making one of their designs, however the cost was rather excessive and I only wanted something which would do the screwcutting..whereas their design was bordering on full cnc.

So I designed my own using Arduino microprocessor boards, the leadscrew control can cut any thread with a reasonable degree of accuracy and will even take into consideration the inaccuracy of the threaded rod 'leadscrew'... The control box can also be used to provide slow motion of the saddle and of course can be sped up to go along faster or slower manualy.

It has taken some time to get things sorted out and I have to admit that headstock drive stepper motor is rather underpowered, however using fine cuts I have made a number of internal and external screw threads, one of which is used on the lathe itself.

It might not be pretty...but it works.

Let me know if you want any more info.. rgds....Bob.

15/03/2015 13:42:30

Hi All... Michael Gilligan wrote on 25/02/15... "Replace outboard gearbox with 'electrickery' & stepper motors"..

Here is one I did earlier using 'electrickery' .

Bob.dsc_0015.jpg

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