LED Strips - illumination



  • I want to fit LED Strips to my Delta for a bit of illumination. I'd like to have PWM control of them via the Duet Wifi board.

    I'm only using one hot end and one variable speed fan - which gives me the option of using either the 2nd Heater or 2nd/3rd Fan driver.

    What's the current capability of the Fan drives?

    If I use the heater (probably the better option) can I control the PWM directly in G Code, without it having to use the PID / Thermistor control?

    Ideally it would be nice to control them from the PanelDue (setting the 'temperature' or 'fan speed'). That's not critical though.

    Thanks in advance,

    Si


  • administrators

    You can connect LED strips to unused heater or fan outputs. See https://duet3d.com/wiki/Using_servos_and_controlling_unused_I/O_pins. The fan outputs should be OK up to about 2A maximum current.



  • If you are connecting the LEDs directly to fan or heater outputs, you should have a super stable power supply, that will hold the voltage even if the bed is heating. If not the LEDs will drop in brightness.
    I had this setup but my power supply (came with the kit from T3P3) drops 1V when bed is heating and the LEDs dimm slightly.
    If your bed is heated bang-bang thats not a big problem. But then I tried to tune the bed with PID and the bed PWM is 10Hz, so the LEDs where flickering like crazy.
    I changed the setup with a little step down converter on 12V Vin and GND, so the LEDs are getting 10V supply, and a MOSFET on Fan2 output (Gate with pullup resistor) LED+ on step-down Vout+, LED- on drain and source on GND.
    Now I can tune the bed and use it with PWM without the LEDs flickering and have the ability to change brightness with the fan2 pwm output.

    I hope it helps,
    Andre



  • Good point, AndreS; I use an ATX power supply, and to my astonishment the 12V circuit drops by about a volt when the heated bed switches on - I can hear it as the fan speeds change. I really would have thought the voltage regulation would be more stable.


  • administrators

    Many ATX supplies need to load the 3.3V and 5V lines sufficiently to prevent droop on the 12V as load increases. This is why the Mendel90 printer came with dummy load resistors for the power supply 5V and 3.3V lines. Long discussion here :
    http://forums.reprap.org/read.php?1,173287



  • Thanks Guys.

    My bed is mains operated, through a SSR and the PSU will source sufficient current for the voltage to stay within 100mV of target (24v). I just have two equal strips of 12v LEDs connected in series. They seem to work pretty well connected to a fan output.

    Si


  • administrators

    bright!



  • Simon you have a leadscrew driven delta? Tell us more….



  • Simon you have a leadscrew driven delta? Tell us more….

    As an experiment, I attached a hot end to my Bridgeport CNC Mill - and was rather pleased with the results! It suffered from none of the motion artifacts I could see on my Ultimaker running at about the same speed.

    I thought a further experiment would be worthwhile, making a far more rigid printer than is common. The printer above is all made from 3mm folded mild steel and uses OpenBuilds linear actuators as the towers

    These were chosen as a reasonable compromise between cost & rigidity. They are not bad - you can adjust out all the backlash and they are pretty rigid / solid.

    I played around with different designs for a couple of days before arriving on this:

    Had the parts laser cut & folded - and it became a printer! It's only been whole for a few weeks and only printing for two weeks. It still needs a fair bit of tuning but it's on track to be pretty good. I printed one part (a simple 200mm diameter cylinder) - and I have never seen as smooth, facet free surface. Unfortunately the print terminated after 5mm due to extruder problems, which hopefully this will fix: http://www.thingiverse.com/thing:1872441 I'm still waiting for the drive gear to show up though.

    Once it's proven and working as well as it can, I'll write it up as an open source hardware project on Instructables.com, along the lines of my CNC Plasma http://www.instructables.com/id/CNC-Plasma-Table/

    Si



  • I like it I've seen one other leadscrew/ballscrew delta. The only issue I could see would be lack of speed, but I don't doubt the rigidity or precision. What type of screw (pitch/lead) are they?

    Will look out for the write up. Be nice to see some video of it working, hope you solve your extruder issue.



  • The screws are 8mm/rev - so half to 1/3 the speed of a belt drive. Running RAMPS, speed could easily be a problem - but not with the Duet!

    This is the very first time it moved under power (no microstepping so motors are not quiet - sounds cool from a SiFi Robot point of view though)
    https://www.youtube.com/watch?v=RHBkGtcOjoc

    This is a week or so on with the very first successful print:
    https://www.youtube.com/watch?v=rIT03o2w2TM
    This was before the SSR to drive the bed arrived - hence using painters tape. This is pretty slow, with low acceleration. Once the gear for the extruder shows up (should have arrived Friday!) I'll video some more at decent speed!



  • I really like the leadscrew approach! My only concern is considering there's a fair bit of torque multiplication going on, I imagine crashing the nozzle into your build surface could cause quite a bit of damage!


  • administrators

    You could control the torque multiplication by using smaller motors with lower torque, e.g. Nema 14. Reducing the current on standard Nema 17 motors would not be so good because the rotor inertia would work against you, and the detent torque would eventually cause the microstep accuracy to degrade.



  • I imagine crashing the nozzle into your build surface could cause quite a bit of damage!
    And you'd be right!
    However, the magnetic ball joints let go before it does any damage.
    The torque multiplication was part of what I wanted. Fast printing needs high acceleration which requires torque.

    On a different (commercial) project I found the stretch in timing belts to be an issue moving the end effector fast - it needed high precision and the elasticity in the belt caused judder in the position. That was solved using lead screws - and hopefully they will benefit this for the same reason.

    Si


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