basculating end effector problem

Hello all! First time poster here.
I'm building my second delta, this time with a double extruder setup but i'm having a very hard time calibrating it. The problem i'm encountering is that the end effector platform basculates, it oscillates along the Y axis if i perform a pure X traslation and along the X axis (albeit less) if i perform a pure Y traslation.
It's not the familiar bowl shape it makes if some firmware constants are not well set, it looks like a mechanical linkage problem of some sort.
I thought it would be a common problem among delta builders so i searched all around the net but with no success, maybe i'm using the wrong terms (i'm not a native english speaker), i don't know...
Anyway i'm here to ask for help, even only a hint in the right direction would be very helpful! Thank you in adavance

Edited 1 time(s). Last edit at 10/23/2014 09:07AM by ZaKKoS.

If the effector is moving in a bowl shape then you need to play with the following numbers.

In my marlin firmware as I recall the number I played with was.

#define DELTA_SMOOTH_ROD_OFFSET 205.9 // mm <- That one.

However you should make sure your setting the rest as accurately as possible.

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Modicum V1 sold on e-bay user jaguarking11

nope
As I said is not the usual bowl shape trajectory. The center of the effector stays level with the base through the whole movement range. however at non center coordinates the effector (and the nozzles of course) are tilted at an angle...

Are your towers equidistant and the rods of equal length?

thanks for the suggestion Ralph, i'll make sure everything's ok tomorrow!

I know this sounds silly, but have you calculated the steps /mm correctly for your particular setup? I would think that the motors are turning a different speed than desired causing wonky movement.

Another thing to check would be motor current, make sure your not overloading the drivers and causing missed steps.

One more thing to keep in mind would be acceleration. Make sure your not trying to move it faster than the printer can handle. (I had this when homing at nearly 1200mm/s, I had to lower that a bit and its no longer an issue)

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Modicum V1 sold on e-bay user jaguarking11

I can't easily confirm the simmetry of my build but i'm working on finding a way to ensure everything's square and if not trying to compensate for tower misallignment in firmware (i.e. not using the -sin_60*delta_radius calculation but putting actual coordinates, any help on HOW to find them appreciated!)

Another thing I have noticed is that my rods joints have a "huge" play. They're a bit slack(?) and as a result the weight of the effector and what's on it moves everything a little. Monday I'll try to get some steel balls and move to a magnetic joint configuration, hopefully minimizing the play so to troubleshoot everything else better.

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jaguarking11
I know this sounds silly, but have you calculated the steps /mm correctly for your particular setup? I would think that the motors are turning a different speed than desired causing wonky movement.

Thanks jaguarking, I admit i haven't performed any test for that in particular, i have assumed (i know, i know... ) that my belt and pulleys + step count were spot on. i'll double check after the weekend!

Quote
jaguarking11
Another thing to check would be motor current, make sure your not overloading the drivers and causing missed steps.

One more thing to keep in mind would be acceleration. Make sure your not trying to move it faster than the printer can handle. (I had this when homing at nearly 1200mm/s, I had to lower that a bit and its no longer an issue)

I don't think so, before upgrading and adding the second extruder my prints were quite good. No signs of missing steps or dimensional instability. Even now if i put a pen in the middle of the effector it stays true to the bed, and the test prints were not "wrong", only the extruder at non center coordinates lifts so much from the bed that the material doesn't stick!


Anyway i'm really thankful for your help guys!