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Positron II First EPP Cut

Discussion in 'Projects on your Phlatprinter 3' started by Darwin, Sep 16, 2011.

  1. Darwin

    Darwin Member

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    Hey Guys:

    A while back I cut a Positron II proof-of-concept proto out of 1/4" fan-fold. It flew well enough for me having forgotten to support the rudder with braces (using the rudder caused all sorts of "interesting" things to happen as a result.) Unfortunately, that was also when my X-axis woes really got traction and I quit wasting foam until I felt I could move forward with a properly calibrated machine.

    Well, tonight I ran my first sheet of 10mm EPP through the PP ///. The original tile cutter Phlatbit worked very well indeed, even on the flexshaft drive. I ran the cut at 50 inches per minute and the edges look to be very, very nice.

    Anyway, here's a pic. I'll post another of the built plane in a day or so. Attached files [​IMG]
     
  2. kram242

    kram242 Administrator Staff Member

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    Darwin, looks like it came out nice! :good:
    Love the holder idea, it lets you use every square inch of foam.
    Thanks for sharing
    Mark and Trish
     
  3. Darwin

    Darwin Member

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    [​IMG]

    Okay, so here's the finished product. I'm setting up with Du-Bro right now to get all the hardware the kits need.

    I flew it yesterday evening and it's awesome. At low rates, it's stable and easily managed. At high rates it's insane. All on an 800 mAh 2S pack and a little red motor from Hobby King. This prototype is actually heavy because I'm using a large speed control.
     
  4. kram242

    kram242 Administrator Staff Member

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    Turned out fantastic Darwin! :doubleup:
    Are you using carbon across the wing for support or leaving it epp?
    Mark and Trish
     
  5. Darwin

    Darwin Member

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    There's actually two CF spars in the wing, CF ribbons in the control surfaces, and CF guys supporting the rudder. The push rods in this prototype are a mix of 1/16" CF and 1/16" FG, but I'll probably just use FG for production. The rods are so short that they're stiff no matter what you use.

    Connections to the surfaces are via Du-Bro hardware, including the control horns. Very easy to do.
     
  6. kram242

    kram242 Administrator Staff Member

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    Sweet How long before your in production? I want to buy one signed from you! :good:
    Thanks brother.
    PM me if you like
    Mark and Trish
     
  7. Darwin

    Darwin Member

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    Writing the instructions now. I need to set up a router template for the wings to cut the main spar slots (very narrow, so I can't cut them on the machine.) Du-Bro should be back to me in the next day or so with bulk hardware pricing.

    So, I'm thinking next week to actually start selling kits. I suppose I should figure out what they're worth at some point so I can set a price, too...

    ;)
     
  8. kram242

    kram242 Administrator Staff Member

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    :good: Nice work Darwin! We wish you all the success you deserve and that you have fun in the process.
    Mark and Trish
     
  9. Darwin

    Darwin Member

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    Fun not happening. The Phlatty is exhibiting extreme unreliability along the X-axis due to skipped steps. Wasn't obvious when cutting the first Positron II proto (although in hindsight I can see it there because I shouldn't have run out of EPP like I almost did based on the CAD.)

    No, it became obvious when I tried to cut a tool board that was 39" long. Not only did it skew to beat heck, but the X-axis pocket I was cutting ended up with ends that looked like a round-toothed squirrel had been at it.

    We need to talk, Mark. Seriously.
     
  10. kram242

    kram242 Administrator Staff Member

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    If you are having skipped steps on the x. It could be from over tightened x belt, which will also cause the foam to skew. If you are actually able to hear the steps being missed try to slow the feeds down and loosen a little tension on the belt. One other thing to look at is if you have the plastic pulley on the X stepper? If you do please let us know. We have found that they are sometimes slipping on the hub causing what looks like missed steps it will need to be replaced with aluminum ones.
    Hope this helps
    Mark and Trish
     
  11. Darwin

    Darwin Member

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    The pulley on my X-axis has the plastic cog with an aluminum hub that the set screw is threaded through. Is this the right one?

    I noticed that the main cogs were mis-aligned by about 1/16". Turns out that one roller was shorter than the other. So I made a 1/16" shim and lined them up. Unfortunately, that did not address the skip.

    I run a back-and-forth test file at 50 ipm.

    I tried not to over-tighten the belt, but I'm unsure of how to tell the difference between "too tight" and "not tight enough".
     
  12. TigerPilot

    TigerPilot Well-Known Member

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    Darwin, you might also check that the two black idler are not binding. While mine where not binding, I choose to change them to two pairs of roller-bearings. Neil, the guy with the electric car gave me that idea.
     
  13. Darwin

    Darwin Member

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    Yoram:

    Idlers are turning. I'll check them with the belt off to assess binding. I have also been contemplating installing bearings in them, but don't have money for it right now.
     
  14. Darwin

    Darwin Member

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    I inserted a Y-step command into my test file and used the Sharpie attachment to generate a visible map of the continued X-axis issues.

    This was run after I made a concerted effort to NOT over-tighten the belt. Skips are still happening, albeit at a lower rate. Note that after the first pass, the band stabilizes for a period of time, but in a shorter range that specified by the cut program. This means that the lost steps were cancelling each other out for a while.

    Eventually, one direction overcomes the other and we can see a "ratchet" action occur where the X-axis is slipping backwards with each iteration. Attached files [​IMG] [​IMG] [​IMG]
     
  15. TigerPilot

    TigerPilot Well-Known Member

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    Darwin, It looks like binding to me, namely binding in one direction only. The +x direction. It's not on the -x direction, when x goes to 0. I checked it on my big screen tv with a ruler. :D In a way, it's almost like a one-way bearing (in a very very simplified explanation).
     
  16. foamlvr

    foamlvr Member

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    I'd look on the back for marks from the rollers slipping, or the foam catching on the front edge of the cutting surface. You may just need a table on the front. Sand the edges of the cutting surface front and back to a radius about the same as the bit that came with the PP. This is just a suggestion, but missing steps in one direction only and so consistently makes me think the foam might be catching on an edge.
     
  17. foamlvr

    foamlvr Member

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    Oh, and Darwin. That Positron II looks pretty cool too.
     
  18. Darwin

    Darwin Member

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    Okay, had a great conversation with Mark today. Gotta love his and Trish' commitment to customer service. Considering all that's had to be faced in bringing something new and innovative to market, they're still able to go the extra mile.

    New pinion is on the way along with a spare timing belt (mine is a bit frayed at the edges.) We had a long chat about X-axis issues and resolutions among other things. I feel like I may be able to wrestle this steer down now.

    I appreciate all the helpful suggestions from you guys in addition to Mark. You never know what's going to click and solve an issue.

    I'm sure once we get this all ironed out, that the PP/// will be solid from now on. This is the last hurdle to clear before I can really start having some serious fun.
     
  19. SilverFox

    SilverFox Member

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    Darwin, please let us know how it turns out. I am having the same issues. I was starting to troubleshoot things when my driver board died on me. Now, I'm out of town and I can't play with any of my toys!! I should have packed one of my micros!
     
  20. Darwin

    Darwin Member

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    I'm going to start a new thread in the PP /// troubleshooting forum. It's my fault for drifting the conversation from "New Projects".

    The Positron II is really cool to fly, btw. It does nifty delta-wing-only tricks that are kind of hilarious to watch.
     

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