Are there problems in my 3D printer design? - Page 1
Forum section: electronics / beginners

author: FlakeyCrust
author_rank: Newbie
timestamp: August 10, 2018, 04:07:47 am
content: 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 theyareconnected.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.

author: hagster
author_rank: Frequent Contributor
timestamp: August 10, 2018, 05:21:36 am
content: 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.

author: brucehoult
author_rank: Super Contributor
timestamp: August 10, 2018, 05:57:16 am
content: 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.

author: FlakeyCrust
author_rank: Newbie
timestamp: August 10, 2018, 06:10:45 am
content: QuoteIt'sbecauseI'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.

author: FlakeyCrust
author_rank: Newbie
timestamp: August 10, 2018, 06:36:17 am
content: Quote from: brucehoult on August 10, 2018, 05:57:16 amI'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.

author: brucehoult
author_rank: Super Contributor
timestamp: August 10, 2018, 06:56:06 am
content: Quote from: FlakeyCrust on August 10, 2018, 06:10:45 amThat'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.

author: FlakeyCrust
author_rank: Newbie
timestamp: August 10, 2018, 07:13:15 am
content: Quote from: brucehoult on August 10, 2018, 06:56:06 amWell 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.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 10, 2018, 01:54:12 pm
content: Quote from: brucehoult on August 10, 2018, 06:56:06 amno 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.