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kbrown

Frankenwheely - Motorising an Opticstar Manual 2" Filterwheel

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I bought an Opticstar 2" Manual Filter Wheel and the plan is to stick an arduino controlled stepper motor on the wheel perimeter to turn it. Magnets and hall effect switches will be used to keep track of the position and which filter is active. The mechanical design is done using the open source apps LibreCAD and FreeCAD. G-code for my CNC mill is produced using HeeksCAD and the mill itself is controlled by LinuxCNC. Electronic design is done using the awesome KiCad which recently has had a massive boost by the propeller heads at CERN.

 

The mechanics is almost done. Still need to etch the PCB and put it together before the real fun begins writing the firmware :)

 

Clear skies,

K

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Edited by kbrown
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Magnets in place. Had to make some space for them inside the housing. So far so good.

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Here's a basic test of the motor and the mechanics. Everything seems to be working as expected. Plenty of torque, barely any backlash and power consumption is very low when the motor isn't used. Due to the gearing the motor does not need to be energized to hold the current position.

Edited by kbrown
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Finally after struggling for a couple of nights I managed to etch a PCB I can work with. Certainly not the best I've made but not too bad considering this was the first time I used dry film for developing the board. Seems I got a pretty bad roll of it as half of it is so wrinkly it was unusable. Anyhoo I'm going with this even though there's a few spots I have to fix. 

IMG_20171006_011415.jpg

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Still don't know what it's the best way to apply this dry film solder mask stuff. Failed several times due to various reasons. This is the best I could do. Not perfect but I'm not wasting any more time on this. It'll work just fine...

 

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Thought I'd practise a bit more with this dry film photoresist stuff and do a sort of a silk screen legend on the other side of the board. Seems to be really hard to get a nice and even result. This will do for now. Think I'll try ink next time...

IMG_20171010_002803.jpg

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Thanks guys. Tonight I made these super high tech plastic component leg formers to aid getting the hall effect switches in the right place :)

 

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Finally got to solder it together. Everything seems to work as expected too. Getting somewhere now :)

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Just about works. Had to move the hall effect switches (Allegro A3144) right against the housing. 1mm further they didn't register the magnets. Let's see if I have to replace them with more sensitive ones... In this test the red led illuminates when at least one of the sensors is active.

Time to start writing the firmware and the INDI driver for this...

 

 

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I got it to run to next filter on start up and identify it correctly using the hall effect switches I chose. Thanks to a tip in the Arduino forums I was able to "increase the sensitivity" and accuracy of the switches by placing some ferromagnetic metal behind the sensors (just screws stuck on them with blue tack for now :)). This will redirect the magnetic fields towards them making them respond more reliably.

 

Still a whole lot of logic to be programmed and the INDI driver too which I haven't even started yet.

 

 

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Had to do a couple of mods. Added a bracket to hold screws on top of the sensors. They'll serve two purposes: They'll prevent the sensors from moving and also redirect the magnetic fields toward them. Also added a voltage divider from Vin connected to one of the free analog inputs so it's able to detect when running from USB power or external power which is needed to run the motor.

 

Preliminary firmware is now on board. Just need to get the INDI driver in a better place so I can start doing proper tests :)

 

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Here's a demo of the first working version of my Frankenwheely arduino firmware and INDI driver talking to each other. Had to add offsets for forward and backward search directions separately as the triggering of the hall effect sensors varied a little depending on the magnet configuration per slot and the direction they approached the sensors. Shouldn't have to tweak these values from here on as they are stored on board in the arduino's built-in EEPROM.

Now I just need to somehow fabricate the lid for this and do some field tests. I could just mill the lid out of a block of plastic using my CNC mill but that feels a little wasteful. Been thinking of getting it 3D printed somewhere instead. Can anyone recommend 3D printing services in the UK?

 

 

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If you have a design for the lid and\or can create an STL file, I could print it for you....

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Thank you Julian. That is very kind of you! I got a reasonable quote from www.3dprint-uk.co.uk so I went with it. I'm printing a few other bits at the same time as well. They're doing them in polished black nylon. I'm curious to see what the result is.

 

Out of curiosity which printer do you have? I've been thinking of geting one as well...

Edited by kbrown

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I have a Prusa I3 Mk2 multi material, a D-Bot, Wanhao I3 & a mini Mendel.... 

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It's horses for courses, best quality - Prusa I3, small & fast - mini Mendel etc...

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A beautiful piece of work - :thumbsup:

I did something similar but ditched the magnets as they were not accurate enough and had too many holes to drill accurately(No CNC ). With advice and help from Robert Brown ,AKA FocuserPro, I switched to light detection resistors(LDR's), led's(2) and only 6 holes(on a 5 filter wheel 1 row of 5 ,1 row of 1 for "home" ). The software auto seeks home and then auto seeks the number of filter wheels on power up - allowing for 3 to 9 filter wheels to be used. 

Nothing as beautifully made as your set up - good luck and clear skies.

 

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Mine is fixed at 5 filters for now but it would not be hard to add the counting. I'm not keeping track of the absolute position of  the wheel. I just run the stepper until one of the sensors detect a magnet. Then I run a little more to see if any other magnets come into "view" so that I can read which slot we're at. On top of this I apply the user defined offset so that the slot is aligned properly. Seems to be very reliable as long as I don't move the sensors. Neodymium magnets are said to lose less than 1% of their flux density over 100 years so that shouldn't be a problem either. Don't know how temperature changes will affect things. Remains to be seen...

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The 3D printed cover for Frankenwheely just arrived. Had them print a few extra parts too due to their minimum order of £40+vat. Totally happy with the result. Might paint these later for an extra protective layer...

IMG_20171110_145823.jpg

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