Poll

Will they make it?

Yes
7 (10.3%)
Yes, but the printer will be a heap of crap
28 (41.2%)
No
33 (48.5%)

Total Members Voted: 68

Author Topic: Delta FDM 3D printer for $179  (Read 27105 times)

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Offline Rasz

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Re: Delta FDM 3D printer for $179
« Reply #75 on: March 01, 2017, 11:21:52 pm »
why steppers at all, go closed loop with custom brushed motor servos - with potentiometers moved from inside servo to the arms of delta and control electronics centralized in main microcontroller, + one optical encoder strip for height.
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Offline Assafl

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Re: Delta FDM 3D printer for $179
« Reply #76 on: March 02, 2017, 02:59:29 am »
Lastly, I do not thing an accelerometer would make a bad job of a auto-levelling sensor. It depends I guess on how close they can mount it to the nozzle, and how they compensate for lag (or do the impact at very slow speeds).

Accelerometers are incredibly sensitive, I expect that the impact with the bed would be completely drowned out by the steps of the stepper motors, which might look smooth to the eye. Even the teeth of a belt or gear might cause noise in the signal.

Have you ever set Z0 incorrectly? While I agree the steps are probably detectable and noisy - the impact of the glass is pretty violent. I guess it is how you do the signal processing.

That said - there was a brief period in which the new version of the firmware could not zero properly and I printed without auto levelling. Worked fine. Of course you need to get those transformation parameters right for it to work against a flat plate of glass.
 

Offline janoc

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Re: Delta FDM 3D printer for $179
« Reply #77 on: March 02, 2017, 03:17:37 am »
why steppers at all, go closed loop with custom brushed motor servos - with potentiometers moved from inside servo to the arms of delta and control electronics centralized in main microcontroller, + one optical encoder strip for height.

Those would likely die even faster than the crappy steppers - cheap brushed motors are not the best choice when you need to actually hold position under load, i.e. the motor is stalled. Steppers are designed for this use, brushed DC motor would likely burn out unless it was hugely overspecced. They are not designed to be stalled.


 

Offline janoc

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Re: Delta FDM 3D printer for $179
« Reply #78 on: March 02, 2017, 03:27:40 am »

Have you ever set Z0 incorrectly? While I agree the steps are probably detectable and noisy - the impact of the glass is pretty violent. I guess it is how you do the signal processing.

A violent impact into the printing surface is likely the last thing you want on any machine where you want some semblance of accuracy and of long term stability. You want to go slow and gently and ideally avoiding any contact at all - that's why various probes with flexible tips are used on CNC machines instead.

Accelerometer would completely suck for this - how would you detect where the vibration from the motors stop and the impact to the surface starts? Especially as the motor is likely still "pushing" when you hit it. This would be both inaccurate and messing up the (already poor) mechanics of the machine.

The simplest way to do this is a contact probe or the various inductive or capacitive sensors. If the bed is non-conductive then optical sensor could be used too.

And if your have a semi-decent machine, you don't need automatic bed leveling at all. You level the bed once and it stays put for a long time. My self-assembled Mendel90 doesn't have it and I have never had a problem. But the Mendel is a fairly rigid and reasonably designed machine where it is not difficult to keep the parts square to each other (unlike the various Prusa i3s and similar). The automatic bed leveling on the consumer printers is mostly a kludge working around the mechanical inadequacies of the design that won't stay square.

« Last Edit: March 02, 2017, 03:29:28 am by janoc »
 

Offline Assafl

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Re: Delta FDM 3D printer for $179
« Reply #79 on: March 02, 2017, 05:27:59 am »
Yup. When well calibrated it works fine. I use 1515 beams with linear carriages and it keeps square (on a mini Kossel). Still use the auto leveling. Don't know why. Use resistive pads under the glass to detect the touch. Works well.

The SNR on the accelerometer will depend on how well it is coupled to the nozzle.
 

Online dunkemhigh

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Re: Delta FDM 3D printer for $179
« Reply #80 on: March 02, 2017, 08:46:53 am »
Quote
an accelerometer would make a bad job of a auto-levelling sensor

I might be wrong, but I think an accelerometer for auto-levelling is a good tool for the wrong job. You don't want the bed to be perfectly level relative gravity, you want it to be perfectly parallel to the rails the hot end is running on.
 

Offline janoc

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Re: Delta FDM 3D printer for $179
« Reply #81 on: March 03, 2017, 07:12:29 am »
Quote
an accelerometer would make a bad job of a auto-levelling sensor

I might be wrong, but I think an accelerometer for auto-levelling is a good tool for the wrong job. You don't want the bed to be perfectly level relative gravity, you want it to be perfectly parallel to the rails the hot end is running on.

No, the idea was to detect the contact with the surface (and thus the printing surface not being perpendicular to the Z-axis) by detecting the impact, not to to measure the angle. That would be useless, indeed. Furthermore, common cheap accelerometers likely don't even have enough resolution for doing such measurement with useful accuracy.

The surface impact could be detected, but accelerometer is not the right tool for that job neither if you want any accuracy and reproducible result.
« Last Edit: March 03, 2017, 07:14:41 am by janoc »
 

Online dunkemhigh

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Re: Delta FDM 3D printer for $179
« Reply #82 on: March 03, 2017, 08:03:07 am »
Quote
detect the contact with the surface

Ah! OK :)
 


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