For a three wheel robot like that, especially running on carpet, I prefer to use a pair of optical mice for movement feedback. It is better if you can use a relay lens to space the mouse sensor up from the floor a little.
@David : I think I have the XY table worked out Proxxon Micromot KT 70 MICRO Compound Table £79 to £86 It gets good reviews from the scientific comunity for accuracy in optical and microscopy usage. Probaly has enough travel to suit the boards I want to make. easily converted to CNC control.
I am afraid I can't answer all your questions.....
- I don't know where you would get an x-y table, but I guess you could get such a thing somewhere...anyone know where?
- I think you'd have to wait a bit before Max will lend you his 3D printer, especially if you want to cannibalise it, but you could always ask :-)
- by a happy coincidence I have two of my little writers. They have a couple of steppers in them for X and Y motion, and a solenoid for Pen up/down. And a uC board for driving them. And a keyboard for inputting the text. It would be a simple matter to rip out the guts and connect the Steppers / Solenoid to something else. If you're serious about this and would like one, I'll send it over....not sure how much the postage would be but it couldn't be worse than the parcels we send to the wife's mom in Zimbabwe.... Let me know.
- If it's a true laser you wouldn't need to up/down it, just turn it on and off. What you would have to worry about is the beam size compared to the step size, the beam intensity and time to correctly expose a "pixel", and whether the sensitised PCB is sensitive to red light (they usually want UV - can you get UV lasers?) You might be able to get a UV LED and focus it with optics....
- There does not seem to be a spell check in these post windows. I can spell, but my fingers don't seem to have mastered it.....
I have been thinking about this for some time. 30 to 40 years ago, I got to like XY plotters when I worked in the LTE labs, where I programmed one to work of an Apple IIe, sadly the plotter is long gone, but I do still have a working Apple IIe.
I am think that XY tables are now coming down in price, so it would be worth a look at using a lazer instead of a fibre pen, to draw on a sensitised surface.
Do you think Max might loan me his 3D printer? It has XY an Z axis movement and the lazer could go in place of the printer head?
Well thats another avenue of research using the cheapest 3D printer, instead of a milling table, which has the greast accuracy?
Your little plotter would be good, now the size of components are shrinking?
What type of laser do I need? Can I use a CD lazer with its constant focus tech.
How do I get my Mac book to spell check on these post boxes while typeing.
> "an XYZ axis plotter with a lazer head, which will write PCB etches direct to photo sensitive resist coated euro boards."
> "Any one up for a Kickstarter project with me on this, or has someone got there before me?"
I'd be in if I could afford it - damn good idea! I got some goodies which were used for writing on drawings - they held a pen and had an X-Y drive and a solenoid to lift / lower the pen. I thought about modifying them - putting a small motor and mill on it but it would weigh too much - drawing pens are pretty light. However a laser diode is a different matter. Also though the X drive was a good few inches the Y drive was only about an inch at the most - enought for writing one or two lines of text. So only very small PCBs. You've obviously given this a lot more thought. Let me know if you get any further with it.
@Max Crusty speaks for me too on this one - what did you want to do with your shaft encoder data? If for speed control or distance measurement you'd get some inaccuracy from slippage - especially if your wheels could be driving at other than 0 degrees to the direction of travel? And I seem to remember you were going to have an on-board accellerometer? From which you could get fairly accurate measurements for speed and distance? Speed control from an accellerometer would (to me) be a fairly horrifying conrtol system to implement, but I seem to remember also that you got your degree in control systems, so to a man of your abilities this should be a mere bagatelle?
Hi Max: I can certainly say that Crusty knows nothing about robot building, but I do wonder about why you need a shaft encoder, and would that be three? one per wheel?
It seems to my mind that DC motors of the old school have comutators and that you can count the number and speed of segments being powered to determine shaft rotation speed. I did this years ago with a guy called John Ewins for a motor speed controller, for a very accurate tape cassette recorder. Design was published in Wireless World probably 35 years ago.
If you are using stepper motors then you know how fast and how many steps you are sending to the motor.
So why the shaft encoder? It will not give any more information about wheel slip versus distance, or does it? and you are still going to have to count the pulses in the Arduino code.
Though I would drop this in as everyone is helping you on the motors at the moment.
I will be going through similar problems as I am going to try to make an XYZ axis plotter with a lazer head, which will write PCB etches direct to photo sensitive resist coated euro boards.
Any one up for a Kickstarter project with me on this, or has someone got there before me?
Max - I've bought a number of motors from Surpluscenter. They have a pretty wide variety. Ov course, since they're selling surplus, you never quite know if you'll be able to buy the same one twice. But they have a good selection and ship things pretty quickly.