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Author Topic: Steppers out of sync and skipped steps?  (Read 8200 times)

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Online Tweakie.CNC

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Re: Steppers out of sync and skipped steps?
« Reply #10 on: February 18, 2011, 08:31:23 AM »
That's the spirit.
You will succeed and have the finest machine in the end.  ;)

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Steppers out of sync and skipped steps?
« Reply #11 on: February 18, 2011, 08:47:22 AM »
hi  dan like tweekie said you have to have the pulleys tight on the shaft. the shafts have to line up.you cant have to much friction .Dont forget you are talking motors with oz. inch of torque not horse power.  If you dont get the machine right you will through up your arms and give up saying cnc is no good for you. And that would be a lye. If you get the machine working right you will be proud of it and will be boasting all over the place about how well you machine works. That is the reason there are so many people on these forums . WE ARE ALL PROUD OF OUR MACHINES AND THE WORK WE CAN DO.. It doesnt matter if you use wood or metal for the build as long as the electronics and mechanicals are the best you can do. So be paitient and take your time with the build in the end you WILL have a good machine. Check with a company called SDP/SI at www.sdp-sl.com they have catalougs with pullys belts etc. good place Oh and by the way hope you are using timing pulleys and belts other wise you will never time your machine...
Re: Steppers out of sync and skipped steps?
« Reply #12 on: February 18, 2011, 09:01:33 AM »
Yeah, timing pulleys and belts of course.

I think my main issue is the bodgy way I have mounted the pulleys onto the steppers. Making some sleeves that fit over the shafts and also perfectly in the pulleys would be the best way, however I do not have access to a lathe, so it's not an easy option.

I am using these pulleys: http://ausxmods.com.au/t5-pulleys/15t5-27-6.35mm-bore-timing-belt-pulley

The stepper shafts are 5mm I believe, however they don't have 5mm pulleys, and I didn't consider the pulleys being off centre.

I suppose worst case I could send a stepper and a pulley off to a friend with access to such machinery, though I don't like relying on everyone else to do everything for me.

My skills in mechanical construction are pitiful, I'm surprised I've managed to make it this far without screwing the whole thing up. Quite proud of how its turned out considering. My electronics knowledge is a whole lot better, luckily.

Here is a picture of my machine as it is now:
 

Ideally I would have loved to use guide rails instead of bearings for the linear system, though as I'm a student, I don't have a particularly huge budget. I do have all the parts required to finish this machine now, but I need to work out the little bugs first. Not even going to think about putting the laser in until it can run without loosing steps.

Cheers,
Dan
« Last Edit: February 18, 2011, 09:18:44 AM by Things »
Re: Steppers out of sync and skipped steps?
« Reply #13 on: February 18, 2011, 09:18:33 AM »
dont feel bad Three years ago I was in the same vote as you .No lathe never built a cnc machine etc. 6 month later I designed and built a machine that would rival the 100,000 dollar machines . And let someone tell me different. Go to a sight call mechmate.com You will be suprised at what they are making. And I mean people from all over the world. they have a forum they sell plans that are one of the best . A couple of years ago the plans were free. now I think they might be 100 dollars. All my motor shafts are 1/4 ingh so are the pully holes. The jack shaft that I use is 1/2 inch it is the same size as the bearings Then I bored out the bigger pullys to fit . On that site I told you about it tells you how to grind rails how to bore pullys without a lathe only a drill press and grinder etc. check it out.

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Re: Steppers out of sync and skipped steps?
« Reply #14 on: February 18, 2011, 10:17:33 AM »
Just a suggestion but some pieces of shim formed around a 5mm drill may make the necessary sleeves to fit between your motor shafts and the pulleys.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Steppers out of sync and skipped steps?
« Reply #15 on: February 18, 2011, 10:19:32 AM »
Hmm I didn't actually think about that. I have a fair bit of sheet aluminium left over from the table of the cutter (So the laser doesn't burn right through it), so I'll try that tomorrow.

Cheers,
Dan
Re: Steppers out of sync and skipped steps?
« Reply #16 on: February 18, 2011, 11:08:08 AM »
Nice machine there .the v wheels are perfect. They will keep track just about as good as 500 dollar linear bearings . That is if they are lined up. But if you took one otor of the end of each axiz and put a idler pully on the end it would save a lot of work. also your machine would be more stable. I would put a shaft all the way across the x axiz or long axiz from one side of the machine to the other put it in pillow block bearings this could be either motor end or idler end that way you could move you machine with one motor insted of 4 motors. much easyer and would look a thousand times better. You machine from what I can see is like the mechmate design. Check there site out you would be suprized by what you see. and they can give you so much information. If you put the shaft on the lmotor end you could gear the motor down . to give more ower . and make it cut smother.also with one motor it will save you hundred of dollars on motors couplings .drivers etc.  nice machine though.
Re: Steppers out of sync and skipped steps?
« Reply #17 on: February 18, 2011, 10:44:37 PM »
It seems you were right larryc.

Today I woke up, and made some little spacers out of .5mm sheet aluminium. The pulleys still aren't EXACT, but much better.

While playing around with it, I noticed that sometimes the belt would actually skip teeth over the pulley!

I cut the wires to 3 motors, leaving only 1 motor for Y, and 2 for X, and it doesn't seem to have any problems now. I am just going to leave the motors in place instead of swapping them with idler pulleys, as they are cheap and saves me having to come up with something else.

Why they wouldn't run in sync in parallel is very confusing, I don't see how they could actually run out of sync. But apparently they can.

My next dilemma is whether to put a bit of weight on the carriages, or whether to add something like runner bearings underneath. The V groove bearings stay on track better if they have a little bit of force pushing them down onto the tracks.

Torque doesn't seem to be a problem as I first thought, which is why I used 2 steppers. You can still stop it with your hand, but that is good in the case of a softlimits or limit switch failure so it doesn't rip itself apart.

Cheers,
Dan
« Last Edit: February 18, 2011, 10:46:53 PM by Things »
Re: Steppers out of sync and skipped steps?
« Reply #18 on: February 18, 2011, 11:26:16 PM »
Well, I'm happy again now :)

Just did my first engraving, using a much smaller laser I just sat ontop, so no blanking yet, but it works :D

Re: Steppers out of sync and skipped steps?
« Reply #19 on: February 19, 2011, 12:05:05 AM »
Sorry for the triple post, but I have a question. Is there any way you can mirror the output in Mach 3 without having to edit the gcode?

I just wrote my name .. backwards >.<



This is soo much fun :D

Cheers,
Dan