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Mukv

DIY Motorised focuser for crayford type focuser

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Greetings

I am new here in the lounge but feel my version of a motorised focuser is worth sharing with others,

The whole project cost less than £28:00 with most parts from Maplins electronics store here in Mansfield.

post-28592-0-66804000-1390068601_thumb.j

The time to build is a little over 3 hours and used some model making tools needle files a small drill and a soldering iron.

If anyone is interested in the details I can post a breakdown of the stages of the build.

Andy

Mansfield Notts

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Hi and welcome to SGL.

Looks great. Please do share how you made, I'm sure lots will find it useful.

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That is a great upgrade when you are able to focus your scope without to touch the focuser! If you want to control it by a computer, you might want to upgrade to a stepper motor and a belt drive later on. Nice to see your mod!

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I've looked into direct usb control and found various circuit diagrams but things get expensive for such a simple project but I have found quite a useful pre made control board that can control DC and stepper motors also servo's all at the same time https://www.pc-control.co.uk/motorbee_info.htm a most useful versatile addition  to diy pc control and maybe useful in other areas.

Andy

Mansfield

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Nice build! Looks very solid. I'd like to see what's in the box!

Hmm. Depending on where you shop (I tend to avoid Maplins, but they can do good discount prices), a clone Arduino Nano microcontroller sells for about £7, sometimes less, a decent stepper motor is about £12 (much less for a 5v motor, maybe £5, which would probably be fine, considering you have a 1.5-3v DC motor there) and an EasyDriver stepper control board goes for about £6. As for controlling it, I've written some simple software to do that, which I'll be happy to share. There are other software resources online too. It would also be easy to make a basic handset-controlled stepper device, if connecting to a PC is inconvenient. Besides eliminating hand-wobble vibration (if "hand-wobble vibration" isn't a recognised astronomy term then it should be!) during focusing, another advantage of a stepper-driven focuser is that you can record the step number of your various targets' focus point, and use that record to quickly find focus next time. This doesn't work so well on solar system objects because their distance varies, but for DSOs it works well. It's hard to get anything like this accuracy with a DC motor, as even under computer control, the only thing software can measure is how long the motor has been running (with a few transistors and resistors added, an Arduino can control up to 6 DC motors). Of course, stepper motors might be an elegant solution to a problem you don't have, but next to the ~£28 you spent, they're certainly not prohibitively expensive. Their main drawback for when you have no access to mains power is that they're power-hungry - unlike DC motors, stepper motors are on and using power all the time, even when not moving, unless you somehow disconnect the power supply.

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love the " hand wobble vibration "  it should be an astro term! in the black box is a pair of battery holders  one holds 2 x 1.2v rechargeable and the other a 1 x 1.2v there is a selector switch to pick the voltage which in turn controls the speed of the motor which is geared 100/1 the led's were  going to detect limit of travel via micro switch top and bottom also direction but it started to take over the idea of keeping it simple and cheap lol. power wont be an issue soon as I am in the build an obs stage of the hobby . the control box is easy to hold hand size but also a nice size for the desk where my camera and guide control is based.I thought about full computer control but when just putting my eye to the eyepiece the hand focuser comes into it's own.

might use computer focus control for a guide scope though..... but that will be later after the rock watching shed is built!

Andy

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Looks very handy.  I'm a big fan of motorised focuser control.

James

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love the " hand wobble vibration "  it should be an astro term! in the black box is a pair of battery holders  one holds 2 x 1.2v rechargeable and the other a 1 x 1.2v there is a selector switch to pick the voltage which in turn controls the speed of the motor which is geared 100/1 the led's were  going to detect limit of travel via micro switch top and bottom also direction but it started to take over the idea of keeping it simple and cheap lol. power wont be an issue soon as I am in the build an obs stage of the hobby . the control box is easy to hold hand size but also a nice size for the desk where my camera and guide control is based.I thought about full computer control but when just putting my eye to the eyepiece the hand focuser comes into it's own.

might use computer focus control for a guide scope though..... but that will be later after the rock watching shed is built!

Andy

Have I got this right - you adjust motor speed by changing the number of batteries in the circuit? If so, you'll probably get away with it on a low-load and low on-time device like that, and if it works then it works. It also won't much bother the motor as you're within its rated voltage range, but it isn't great circuit design - conventional wisdom is to use a pulse width modulator (PWM) / H-bridge control circuit. The PWM uses less power, it enables controlling the speed with a potentiometer and would draw power from all the batteries to evenly distribute the power load, while the H-bridge part of the circuit controls motor direction. That said, I can't find a commercial 3v bidirectional PWM motor controller, possibly because most PWMs are based on the NE555/6 timer chip, whose operating voltage ranges 4.5 - 15v. I appreciate keeping it cheap and simple, but imo PWMs add a little elegance and a lot more control than varying the voltage, and by keeping impedences even, they help keep components happy! If you're handy with a soldering iron then it'd cost peanuts for parts to build a suitable circuit, and your effort will be well rewarded - heh, my own objective seems to be to find the cheapest and simplest way to do it right, but cheap doesn't always mean simple! If you're building an obsy then eventually you'll almost certainly have some 12v DC power supplies about, in which case if you wanted to upgrade without going to steppers (or just to do away with replacing/recharging batteries), it'd be easy to find a geared 12v DC motor and suitable ready-made PWM controller (maybe £10-12 for both).

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Stepper motors do not need to be expensive;

http://www.ebay.co.uk/itm/Stepper-Motor-DC-5V-ULN2003-Driver-Test-Module-Board-5-Line-4-Phase-f-Arduino-/111247480821?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item19e6ddd7f5

And controller;

http://www.ebay.co.uk/itm/Adjustable-Speed-CNC-Stepper-Motor-Driver-Control-Board-6-4-wire-2-phase-2A-/190685857371?pt=UK_BOI_Industrial_Automation_Control_ET&hash=item2c65c3465b

I believe you can drop one of the wires from the motor to make it 4-wire, maybe somebody with better knowledge can confirm this please?

A bit more digging on e-bay may give more choices.

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Thanks for all this information guys... looks like a bit of spending coming up and a few hours in my man cave with a soldering iron and a laptop open! :grin: this coming weekend.

Andy

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I've been thinking about a motorised focuser for a while. One question that's been bugging me though is how to you go on with the focus lock? or don't you need it?

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Greetings

The focus lock is easy to reach in this setup if you need it, I have used it from time to time when using DSLR but it can handle the weight without any problems even after slewing.

Andy

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Thanks for all this information guys... looks like a bit of spending coming up and a few hours in my man cave with a soldering iron and a laptop open! :grin: this coming weekend.

Andy

You're welcome!

Just looked on this site, it seems to have lots of goodies for a new focuser project.

http://www.technobotsonline.com/

Andy

Yep, looks like a lot of fun could be had from there! They have off-the-shelf PWM controllers (but again, I can't see a 3v one - looks like they supply mainly for high-power robotics), or steppers if you want. Their prices are ok considering they're not eBay. Without looking too hard on eBay, here's a robust 6-24v bidirectional PWM board: -click- and a 12v 80 rpm geared DC motor: -click-. If you have a 12v supply then once that's wired in you need nothing more.

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