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DIY Focuser Design

Mav359

By Mav359
in DIY Astronomer

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Mav359

Mav359

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slightly updated design, pretty much to scale now.

Ive decided to put all the connections on header pins to keep it modular and use a matrix strip to fill in the middle. The power, Arduino board will still be mounted in a box on the tripod close to the USB hub, that way i only have one cable drop off the OTA. I might put a power switch on that box so i can kill the power whilst its standing still.

I have now managed to order a 62mm Dia timing pulley that will fit over the focuser shaft and a 16mm Dia Timing pulley for the motor, these were as far opposite in size range as i could get, it also now means it will be geared correctly. Once i  have assembled it all i'll have an exact center point distance which i can give to cross-morse who can then make me a belt to fit. I reckon i know it but that can wait till i'm sure.

I reckon i have spent about £80 so far, compared to the £700 it would have cost me had i bought so if it works as planned its the best value for money DIY i have ever done

:grin: :grin: :grin: :grin:

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Mav359

Mav359

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In true Iron Man style i give you the (incomplete) Mark I.

Still waiting on a lot of bits to turn up including the Ardunio board & i still need to order the timing belt but so far so good.

I have had to change a couple of things, the RJ11 is (will be) located around the side of the project box  and i'm putting all of the electrics into the same box down south somewhere.

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Mav359

Mav359

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Can anyone tell me how long my timing belt needs to be? The tech guy at Cross Morse is out till Tuesday but if someone can work it out for me i could get it ordered today

The center distance between pulleys is 113mm,

the small pulley has a 16.17mm Diameter

the large pulley has a 64.68mm Diameter

Cheers

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Chris Rowland

Chris Rowland

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There's a calculator here http://www.technobotsonline.com/timing-pulley-distance-between-centres-calculator.html,  it works in numbers of teeth, teeth pitch and belt length to give the distance between centres.

Guessing 40 and 10 teeth and 5mm pitch gives a belt length of 356mm.  I've never done this before but it looks as if it might give you some useful information.  I guess belts don't come in that length and you need to adjust the distance to match the belts sizes that are available.

BTW I don't see how you can have a 6:1 ratio because the diameters you quote are in a ratio of 4:1.

Chris

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astromerlin

astromerlin

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Hi Alan, It's all good. Counting teeth is ok as the diameters work out roughly right, I've been retrofitting CNC machines for years and have always geared by teeth count. If you need absolute precision you can adjust the gearing in code. If you need more gearing then code microstepping in the Arduino.

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Mav359

Mav359

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:grin: :grin: :grin: :grin:  :grin:  Well the MARK I works........

i put it all together and so far so good, i'm happy enough with the Pulley end of the design but dropped a glanger with the box of electronics. The project boxes i had were two small for me to get all the bits in so i put the boards in different boxes and gaffer taped them together. Ive ordered the timing belt so that is the last step.

As it does work as expected & because i now know i can do it there will deffo be a MARK II  version of the elctronics box, smaller, better placed on the tripod etc....

The software does do the job but its very basic, is there anything else from a software point of view it will work with?

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opticalpath

opticalpath

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Ok Cool

 

Does it matter in this case? Is 4:1 enough?

 

I ask that like i can change it but i doubt i could.

I'm sure it's the ratio of teeth that gives the accurate reduction factor. The quoted diameters may just be nominal anyway .... and do they mean inside or outside diameters, the toothed part or the larger outer guide fence? :confused:  

 

Think of it this way: suppose you make an index mark on the belt. One full turn of the 60-T pulley moves the belt on by 60 notches from the index mark.  Now imagine the belt passing over the smaller 10-T pulley.  A movement of 60 notches on the small pulley means the index mark has to pass over 60 teeth, and that means 6 revolutions of the 10-T.  So it's 6:1 (or 1:6 driven the other way), regardless of the quoted nominal diameters of the pulleys.

 

Adrian

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opticalpath

opticalpath

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Nice job. The EasyDriver certainly makes life easier IMO. Its one disadvantage: heed the warning never to connect or disconnect the motor whilst the driver board is powered on, otherwise you will probably kill the driver chip. If, like me, you have a remote box containing the electronics, and a plug and socket arrangement to connect the motor ..... use a locking type connector. It's very easy to pull that plug and forget to power off first :eek: .  I also wired in a LED near the socket to remind me

Adrian

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