MK2S Molly (Multi Material Dolly) Build Log

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TheBat
Posts: 13
Joined: Thu Jun 15, 2017 12:18 am

MK2S Molly (Multi Material Dolly) Build Log

Post by TheBat » Sun Aug 27, 2017 2:31 am

Since purchasing the Prusa i3 MK2, I've wanted the Multi Material upgrade, however 300USD+Shipping+ the 3-4mo wait list is a bit more than I want to commit to. So I am sourcing the Multi Material upgrade parts and building it myself. Since this is a MM Dolly, I'm calling it Molly.

1. I have read through the upgrade manual and determined the new parts list:
I've put it on a Google Doc for convenience
Total cost for me (including a spool of orange ABS) was ~110USD. Some of the hardware can be sourced from the old extruder and the spare parts bag that came with the original printer, so your milage will vary. Keep in mind you could probably source more things off AliExpress than I did to get your costs down, but I didn't want to skimp on the motors or tube fittings.

2. The Official kit comes with a new hot end, so I had to figure out what the differences are. So I asked on the Prusa Forums. Looks like the PTFE tube just needs to be modified as per this page on Prusa's site.

3. The new dual geared extruders use a pinioned and hobbed gear sourced from Bondtech, which cost 50USD for a single set. Buying 4 of those (200USD) is out of the question for me, so I have a 3d printed solution in the works that should be cheap and easy, but will require minor changes to the new extruder housing.

4. For the Extruder Motor Switch Board I will either have to order from Prusa (If they make it available) or reverse engineer from the firmware changes. Seems like it should just a MUX and some relays.

5. I did not source parts for the Spool holders, since these should be a sufficient replacement: https://www.thingiverse.com/thing:2047554

My order from Amazon is set to come in a week, and my order from AliExpress is set to come in a month or so.

Todos:
  1. Source hardware
  2. Print Parts
  3. Stepper Switcher Board
  4. Modify Hot End tubing
  5. Design new Dual Extrusion drive
  6. Build it
  7. Work in Single Extrusion Mode
  8. Print with it
Update 8/28/2017:
I have figured out what I am going to do for the for the extruder switching board. I found a 16-channel(4-bit) Multiplexer and an 8-channel relay board. The multiplexer cost me $2.50US and the relay board cost $7.00US for a total added cost of ~$10US. It's definitely not going to be as compact or as clean looking as the official solution, however it should be functionally equivalent. These should be last parts that I need to actually buy, and I have updated the parts sheet.

Update 9/12/2017:
I received a few parts in the mail last week, check the post below for more details.

Update 9/25/2017:
I finally have a working extruder prototype! See below for more details.
Last edited by TheBat on Tue Sep 26, 2017 4:40 am, edited 5 times in total.

TheBat
Posts: 13
Joined: Thu Jun 15, 2017 12:18 am

Re: MK2S Molly (Multi Material Dolly) Build Log

Post by TheBat » Sun Aug 27, 2017 2:32 am

Building the extruder:
Here are the final parts I used for my prototype extruder.
Image

Below are the replacement for the bondtec dual extruder gears. Two 10t, 155p gears that I printed for a 5mm shaft with a slotted key. You'll notice that one of the hobbed gears is slightly smaller that the other, I had to turn it down form 9mmOD to ~7.5mmOD. Without this, the filament biting portion could not close enough to actually grab the filament. This solved that problem.
Image

The springs that I originally ordered were too stiff and large, so I just grabbed an 8 pack of cheap bic pens and used the springs out of those. They are roughly the correct size and a stiffness that works well enough.
Image

This is my redesigned idler:
Image
Instead of using a 3mm shaft and a bearing between the shaft and the gear, I've decided to use a 5mm keyed shaft that steps down to 3mm shaft which rides in a 630 bearing (6mmx3mm). The shaft itself is 3d printed.
Image

It works!!!
Image
Last edited by TheBat on Tue Sep 26, 2017 4:52 am, edited 3 times in total.

TheBat
Posts: 13
Joined: Thu Jun 15, 2017 12:18 am

Re: MK2S Molly (Multi Material Dolly) Build Log

Post by TheBat » Sun Aug 27, 2017 2:33 am

Reserved for pictures of final results and first successful prints.
Last edited by TheBat on Tue Aug 29, 2017 2:41 am, edited 1 time in total.

Tsunamijuan
Posts: 21
Joined: Mon Jun 19, 2017 5:34 pm

Re: MK2S Molly (Multi Material Dolly) Build Log

Post by Tsunamijuan » Sun Aug 27, 2017 6:24 am

The original Multi material kit for the Prusa was displayed with a Plastic Quad Y adapter Manifold. However after much testing, Josef Prusa concluded that using a plastic manifold didn't work reliably due to the varying thicknesses of filaments. So the Release version of the kit uses a metal Manifold. I have yet to see pictures of the metal version probably to prevent it from being copied until they no longer have a backlog of orders when it will be released spec wise.

As for the motor switcher board, its not really a switcher at all its just an extension of the PWM channels to drive the additional stepper motor controllers. There is information on the reprap wiki about using the common GRBL cnc sheild with a standard Arduino Mega controller with a ramps board. To add an additional 4 stepper motors. At this point you need to do minimal code changes in the arduino code, they should then be mapped as E2-E5. You then use the tool change event in supported multi material slicing software to load and unload the filament. (ie e0 retract 20mmm, E1 extrude 20mm).

One of several RepRap Wiki posts about this http://reprap.org/wiki/Adding_more_extruders .

I spent alot of time digging into the inner workings so i could do the same thing but without being locked into the Prusa i3 (i am not a fan of printer beds that move in the the X and Y directions). Hopefully this helps you out quite a bit.

TheBat
Posts: 13
Joined: Thu Jun 15, 2017 12:18 am

Re: MK2S Molly (Multi Material Dolly) Build Log

Post by TheBat » Sun Aug 27, 2017 7:49 am

Tsunamijuan wrote:
Sun Aug 27, 2017 6:24 am
The original Multi material kit for the Prusa was displayed with a Plastic Quad Y adapter Manifold. However after much testing, Josef Prusa concluded that using a plastic manifold didn't work reliably due to the varying thicknesses of filaments. So the Release version of the kit uses a metal Manifold. I have yet to see pictures of the metal version probably to prevent it from being copied until they no longer have a backlog of orders when it will be released spec wise.

As for the motor switcher board, its not really a switcher at all its just an extension of the PWM channels to drive the additional stepper motor controllers. There is information on the reprap wiki about using the common GRBL cnc sheild with a standard Arduino Mega controller with a ramps board. To add an additional 4 stepper motors. At this point you need to do minimal code changes in the arduino code, they should then be mapped as E2-E5. You then use the tool change event in supported multi material slicing software to load and unload the filament. (ie e0 retract 20mmm, E1 extrude 20mm).

One of several RepRap Wiki posts about this http://reprap.org/wiki/Adding_more_extruders .

I spent alot of time digging into the inner workings so i could do the same thing but without being locked into the Prusa i3 (i am not a fan of printer beds that move in the the X and Y directions). Hopefully this helps you out quite a bit.
Thanks for the info, especially on the switching board!

As far as the metal manifold, the build manual shows how it works. Small metal tubes are inserted into the plastic manifold. They are labeled as "Cooling Tubes" in one of the troubleshooting guides about dealing with filament stuck in them. I think the main reason for them is for printing ABS and higher temp materials that may fuse to the sides of the plastic manifold. That all being said, I managed to find some steel tubing on Amazon that I will just have to cut to length, so the metal design can be replicated.

Tsunamijuan
Posts: 21
Joined: Mon Jun 19, 2017 5:34 pm

Re: MK2S Molly (Multi Material Dolly) Build Log

Post by Tsunamijuan » Sun Aug 27, 2017 9:53 am

Well there is the fact too that they where printing some of the stuff before for the manifolds. If you watch the tolerances of prints closely, even more so on a production high speed printing environment. You find that there are points that tend to end up miss shapen, its far worse with ABS which is what they primarily print with, since it handles the high temperatures better than PLA or similar plastics. Those tolerance issues makes metal a much better choice.

If you know the angles you want use you should fairly easily be able to drill a small block of metal with a hand drill to be your manifold.

If I get to the point of building a manifold before you do, I will make sure to post my design results and model for you to make use of.

TheBat
Posts: 13
Joined: Thu Jun 15, 2017 12:18 am

Re: MK2S Molly (Multi Material Dolly) Build Log

Post by TheBat » Tue Aug 29, 2017 2:56 am

Tsunamijuan wrote:
Sun Aug 27, 2017 6:24 am
As for the motor switcher board, its not really a switcher at all its just an extension of the PWM channels to drive the additional stepper motor controllers. There is information on the reprap wiki about using the common GRBL cnc sheild with a standard Arduino Mega controller with a ramps board. To add an additional 4 stepper motors. At this point you need to do minimal code changes in the arduino code, they should then be mapped as E2-E5. You then use the tool change event in supported multi material slicing software to load and unload the filament. (ie e0 retract 20mmm, E1 extrude 20mm).

One of several RepRap Wiki posts about this http://reprap.org/wiki/Adding_more_extruders .

I spent alot of time digging into the inner workings so i could do the same thing but without being locked into the Prusa i3 (i am not a fan of printer beds that move in the the X and Y directions). Hopefully this helps you out quite a bit.
I looked more into the switcher board. Looks like Prusa will only sell you one if you have proof of purchase for the MM update. I zoomed in the on the pictures from the assembly instructions to get the part numbers on the chips. The official board has 3 or 4 2-channel relays. The only source I could find for those actual part numbers had a minimum purchase quantity of 1000 units, so I'm just going to use a cheap 8 channel board I found on amazon.

I also looked into the firmware for any changes, and found the change_extr function:

Code: Select all

switch (extr) {
case 1:
	WRITE(E_MUX0_PIN, HIGH);
	WRITE(E_MUX1_PIN, LOW);
	WRITE(E_MUX2_PIN, LOW);
	
	break;
case 2:
	WRITE(E_MUX0_PIN, LOW);
	WRITE(E_MUX1_PIN, HIGH);
	WRITE(E_MUX2_PIN, LOW);
	
	break;
case 3:
	WRITE(E_MUX0_PIN, HIGH);
	WRITE(E_MUX1_PIN, HIGH);
	WRITE(E_MUX2_PIN, LOW);
	
	break;
default:
	WRITE(E_MUX0_PIN, LOW);
	WRITE(E_MUX1_PIN, LOW);
	WRITE(E_MUX2_PIN, LOW);
	
	break;
}
Which is controlling a 3 bit MUX with some of the exp gpio pins on the rambo board similar to how the LCD works. I think it's interesting that they chose to use a 3-bit mux when 4 extruders only requires a 2-bit one (Maybe they plan to release a plug and play 8 material upgrade down the line). So long as I get the pinout correct, this should be a plug and play solution that does not require any FW changes. The only thing that I can think of is this relay and mux combo might be slower than expected and I'll have to put a small delay in the code to account for that.

Tsunamijuan
Posts: 21
Joined: Mon Jun 19, 2017 5:34 pm

Re: MK2S Molly (Multi Material Dolly) Build Log

Post by Tsunamijuan » Tue Aug 29, 2017 6:19 am

Interesting, I had started playing with my stuff long before the final release. So I figured he had gone closer to that had been done in the RepRap blogs and docs. Since its also possible to multiplex PWM signals. Though like i said before most of the arudino mega setups have enough spare pins to allow you to just use those with that cnc board. That CNC board off banggood cost me 10$ i think with a uno and all the step sticks.

TheBat
Posts: 13
Joined: Thu Jun 15, 2017 12:18 am

Re: MK2S Molly (Multi Material Dolly) Build Log

Post by TheBat » Wed Sep 13, 2017 1:29 am

Updated.

TheBat
Posts: 13
Joined: Thu Jun 15, 2017 12:18 am

Re: MK2S Molly (Multi Material Dolly) Build Log

Post by TheBat » Tue Sep 26, 2017 4:53 am

Updated with a working extruder!

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