Author Topic: Are there problems in my 3D printer design?  (Read 673 times)

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Offline FlakeyCrust

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Are there problems in my 3D printer design?
« on: August 10, 2018, 04:07:47 am »
I'm trying to build a 3D printer. Unfortunately, I only have a basic understanding of electronics. I have encountered some problems and it would be nice if I could verify that my design is sound before doing any more troubleshooting. I'm mainly worried about signals or power going to the wrong connections, so I have omitted the resistance and capacitance values from my diagram. I haven't had any problems getting the components to work individually (although I haven't been thorough in testing them).

I have included the schematic as an attachment. The wires are colour-coded. Red lines are connected directly to +5V, orange lines to +12V and black lines to a common ground. The rest of the wires are blue. It should be noted that the actual wiring is not represented by this schematic. For example: I have wired the components as if the 5 and 12 volt rails have separate grounds, but the power supply I'm currently using only has one set of ground wires, so they are connected.

Edit: I just noticed that for the 2 channel relay, ground is connected to GND, COM1 and NC2. It should be GND, COM1 and COM2. Please disregard this; it's only a mistake in the schematic.
« Last Edit: August 10, 2018, 04:14:49 am by FlakeyCrust »
 

Offline hagster

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Re: Are there problems in my 3D printer design?
« Reply #1 on: August 10, 2018, 05:21:36 am »
Are you sure you want to design your own main board? There are loads of cheap boards availiable.

Seems like you are using a DC motor for the z axis. How will you accuratly position this?

The mode and enable pins on your steppers are floating.
 

Offline brucehoult

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Re: Are there problems in my 3D printer design?
« Reply #2 on: August 10, 2018, 05:57:16 am »
Yes, not using a stepper for the Z axis seems wacky. That's the thing that needs the MOST precise control in the whole printer!

Also a relay to control the hot end heater?  You want to keep the temperature steady to certainly 1 degree or so, and under a variety of load conditions (e.g. feed rates). It needs to be controlled by a PID algorithm. So you *really* want a PWM output there, going through a MosFET, not a relay.
 

Offline FlakeyCrust

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Re: Are there problems in my 3D printer design?
« Reply #3 on: August 10, 2018, 06:10:45 am »
Quote
Are you sure you want to design your own main board? There are loads of cheap boards availiable.

Seems like you are using a DC motor for the z axis. How will you accuratly position this?

The mode and enable pins on your steppers are floating.

It's because I'm using a DC motor for the Z axis that I'm not using an existing main board. I actually got the motors from an old printer that broke down (a cheap plastic gear broke) and a really old printer I bought used for next to nothing. The stepper motors were rather small, and seemed inadequate for the Z axis, considering the weight, but there was also a rather beefy DC motor. So I decided to use that with a reduction gear made from the remaining gears.

Near the top left corner of the schematic is a box containing an LED and photo-transistor: that's a photo-interrupter. The motor spins a disk with uniformly spaced holes and the photo-interrupter will count how many holes go by, to measure the exact amount of rotation.

As for the floating pins: I just looked at the A4988 documentation and it says the MSx pins already have pull-down resistors, but it doesn't say anything about ENABLE having one, so I will add resistors for the ENABLE pins.

Thanks for taking a look.
 

Offline FlakeyCrust

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Re: Are there problems in my 3D printer design?
« Reply #4 on: August 10, 2018, 06:36:17 am »
Also a relay to control the hot end heater?  You want to keep the temperature steady to certainly 1 degree or so, and under a variety of load conditions (e.g. feed rates). It needs to be controlled by a PID algorithm. So you *really* want a PWM output there, going through a MosFET, not a relay.

I'll change that. I might just use another heat bed module (which is basically just a MOSFET) for the hot end, since I have a spare.
 

Offline brucehoult

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Re: Are there problems in my 3D printer design?
« Reply #5 on: August 10, 2018, 06:56:06 am »
It's because I'm using a DC motor for the Z axis that I'm not using an existing main board. I actually got the motors from an old printer that broke down (a cheap plastic gear broke) and a really old printer I bought used for next to nothing. The stepper motors were rather small, and seemed inadequate for the Z axis, considering the weight, but there was also a rather beefy DC motor. So I decided to use that with a reduction gear made from the remaining gears.

That's kinda backwards. The Z axis is critical on positioning but very very low on power needs. Sure, it might be moving some heavy stuff, but it's only got to move it a fraction of a mm somewhere between once every five seconds and once every five minutes. Sufficient reduction gearing to let you do it precisely enough with a DC motor and optical counter will also let a wimpy stepper do the job.

The X and Y axis have HUGE acceleration and speed needs in comparison. A thousand times more, I guess.
 

Offline FlakeyCrust

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Re: Are there problems in my 3D printer design?
« Reply #6 on: August 10, 2018, 07:13:15 am »
...

That's kinda backwards. The Z axis is critical on positioning but very very low on power needs. Sure, it might be moving some heavy stuff, but it's only got to move it a fraction of a mm somewhere between once every five seconds and once every five minutes. Sufficient reduction gearing to let you do it precisely enough with a DC motor and optical counter will also let a wimpy stepper do the job.

The X and Y axis have HUGE acceleration and speed needs in comparison. A thousand times more, I guess.

Well I'll see how it goes. I already have the hardware built. If it doesn't work, I'll make changes with this in mind.
 

Offline Mechatrommer

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Re: Are there problems in my 3D printer design?
« Reply #7 on: August 10, 2018, 01:54:12 pm »
It's because I'm using a DC motor for the Z axis that I'm not using an existing main board.
That's kinda backwards. The Z axis is critical on positioning but very very low on power needs. Sure, it might be moving some heavy stuff, but it's only got to move it a fraction of a mm somewhere between once every five seconds and once every five minutes. Sufficient reduction gearing to let you do it precisely enough with a DC motor and optical counter will also let a wimpy stepper do the job.
no its not imho. if done properly it can be done. stepper motor is not a holy grail in position control, people even developed (expensive) closed loop system for it to solve its drawbacks. just as the same as brushed and bldc motors.
It's extremely difficult to start life.. one features of nature.. physical laws are mathematical theory of great beauty... You may wonder Why? our knowledge shows that nature is so constructed. We simply have to accept it. One could describe the situation by saying that... (Paul Dirac)
 


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