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Old 05-23-2017, 03:42 AM   #51
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Oh the 3D printer. Now there’s a sirens call that keeps niggling at the back of my brain.


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Old 05-23-2017, 01:08 PM   #52
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I thought I'd just poke my nose in after reading about concerns regarding accuracy when dividing. You should not be using floating point maths anywhere because you will end up with accumulated rounding errors. It like using a micrometer with a coarse scale. Accuracy can not be better than 0.5 of the smallest division as I was taught and we had to accumulate the error +- the measuring unit when doing maths with such readings. It is far better to reduce everything to the smallest discrete unit you can measure. So if you measure divisions in seconds rather than the much coarser degree, a lot of problems go away. Others will appear though as you need to present the angle to the user. I chose to do this in degrees minutes and seconds.

So by working in smaller units you may only be one step out per division and if you want to go one step further to improve accuracy, you can add and subtract a step or two every alternate division to make the error go away by the time you get round the circle.

Finally, let me just say if you are old enough to remember programming on an 8 bit PC, using floating point maths was fraught with danger due to ongoing errors accumulated from converting to and from decimal numbers and hexadecimal numbers used internally in the machine architecture. 16 bit is not as bad but the issue is still there. Most accounting programs will use a binary coded decimal as the numerical unit to ensure accurate results. Regrettably, few programming languages support such a data type.


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Old 06-08-2017, 07:22 PM   #53
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Hi

Well after trying to fudge the numbers to get my indexer to work with an odd reduction without success, I gave up the idea of using a stepper motor with a gear box. Digging through my odds and ends box I came up with a 36 to 1 worm gear set. Coupled with the existing 2.5 to 1 timing belt reduction I came out with 90 to 1 reduction.

Note that when choosing a reduction your steps times your reduction must divide evenly by 360. I am using 200 steps per rotation, 90 to 1 reduction so 200 * 90 / 360 = 50, and that works. I tried using half steps 400 * 90 / 360 = 100 but that didn't work,


The worm gear has about the same amount of backlash as the stepper with a gearbox. To eliminate that I am using a counter weight. Will need to cast a better weight, the one in the photo is just to test the idea. Will also need to provide a second idler wheel to hold the weight off when the table is cranked all the way back.

The electronics as well as the 12 volt power supply were fitted inside a project box. The fitting for the 110 volt inlet also provided a fuse and an off on switch. To keep the box from heating up a 1.5” computer fan was installed in the backside of the box.

All and all I'm very pleased with the system.

Mark T
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Old 06-08-2017, 08:38 PM   #54
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Nice job, Mark. Can you share the source and specs of the project box? Is it perchance, 3d printed?

Chuck
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Old 06-08-2017, 09:20 PM   #55
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Hi Chucketn

Here is a link to amazon. com for the box. Note it took a few weeks to get

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

And here is the link for the power inlet

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

And the power supply

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

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Old 06-08-2017, 11:30 PM   #56
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Thanks, Mark. I asked because I also built an Arduino based set up and need a box to finish it off. I also just built a 3d printer and would like to print same.

Chuck
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Old 07-13-2017, 06:58 PM   #57
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Bob, that is awesome! thanks for the lesson and example.
is there a way to tell the Arduino you want a specific number of index? say for example, you want 48 teeth....can you just type 48 in the LCD and it will figure out the angle to move? (7.5degrees)
Also, I PM'd you on a question I have with my project. I don't want to hijack your thread with my project.
thanks
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Old 07-13-2017, 07:16 PM   #58
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Quote:
Originally Posted by dmh13433 View Post
is there a way to tell the Arduino you want a specific number of index? say for example, you want 48 teeth....can you just type 48 in the LCD and it will figure out the angle to move? (7.5degrees)
The sketch allows selecting divisions or degrees, then you enter the value via the keypad. I built the same setup for my rotary table, but it's still rough. I need to print an enclosure and add a connector for the power and the stepper.
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Old 07-16-2017, 08:02 AM   #59
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Hello all of you!
Sometimes when you see something it says clonk in the head "That should i build".
This was such a thing.
Ordered missed components, draw a nice box and 3d printed it, hooked it up and its working.
BUT!
I use it for my 4th axels thing to my cnc router. 200steps/rot, beltgear 1:3 and it is impossible to get the controller to give the right steps. I need 1200 and get 1040. Fiddeling with numbers in the script only change between 1040 and 1440steps.

Any tips?
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Old 07-16-2017, 04:58 PM   #60
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Quick and Dirty for 1200 steps . . .
change line 'for(int i = 0; i < tm; i++)' to 'for(int i = 0; i < 1200; i++)'

steps [200] and table ratio [3:1] look to be too coarse for an accurate 'Multiplier' value.
Multiplier = (StepsPerRotation * TableRatio)/360;


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