William

wkhs

starter

15/07/2018 at 15:26

@seanpo tachometer (tacho, speed) measures the rotation speed of the shredder shaft in rpm. If it drops below its working speed, something is wrong so the power should be cut out. That’s a fail safe measure I was trying to add.

wkhs

starter

11/07/2018 at 07:37

Just in case anyone is interested in the programme, here you go:

PID Firmware for Injection

wkhs

starter

11/07/2018 at 07:30

Hi all,

I’m planning to upload the firmware and PCB here.
https://drive.google.com/drive/folders/1-CQXoi1p293H7V2ABN1w5_qbTKHo4KnM?usp=sharing

Do note that they are <span style=”text-decoration: underline;”>not ready for release</span>. (Theoretically they could blow your home up — well, just a disclaimer).

Jokes aside, note the following before you order a pcb.
1. I could remember there is a manual reroute after the PCB was made. It should be the pin A7 (it should not be used a digital pin as it was in the scheme).
2. Be ready to install some dependencies (libraries). My habit is to make a copy of the library directly in the project folder so that I don’t have to install them again. But I didn’t do the same for u8glib (if I remember correctly).
3. The tachometer part is almost done. It can count rpm but it doesn’t stop the machine if it goes wrong.
4. Check the pin configuration of the AC transformer

wkhs

starter

11/07/2018 at 06:28

@xxxolivierxxx: I didn’t have time to work on our injection machine since I graduated. Nth to post sadly.

@andyn: I tagged it belated because it was posted 1/2 year after the shredder was functional already. Now it comes to others’ attention after >1 year. Aha!

wkhs

starter

29/07/2017 at 17:39

Count me in!

wkhs

starter

16/07/2017 at 05:45

@jerzeek, thanks for mentioning. I was planning to release the full schematics. But as I started my internship, I didn’t have time to correct the files.

wkhs

starter

31/05/2017 at 13:43

@iammashed, here are the electronics that I bought…

PID controller
SSR: Fotek SSR-40DA (it’s capable of passing 40 amperes and an overkill for this purpose, but an overkill also means greater safety margin)
Band heaters: ID 30mm x H 45mm (operated at 220V 0.6A each, i bought 4. they can heat the tube at around 1 deg celcius / second)
Thermocouples

I built my PID controller with thermistor myself. That said, I would suggest you find a controller with autotuning. Most controllers can interface with all thermocouples so no worries about that. However, you need to buy a thermocouple which can safely operate in the range. For example, if you want to melt PET at around 260 deg Celcius, get one that works at least up to 300 deg Celcius and the higher the better (again overkill means greater safety… hmm if you forget about the precision and nonlinearity problem)

wkhs

starter

14/05/2017 at 17:44

@davehakkens we added an encoder to detect stalling. But a overcurrent protection shall do the job too.

wkhs

starter

08/05/2017 at 15:21

3. Motors

Men love motor – I just can’t tell why. We started using a combo with 1.5kW 1400RPM on 1:40 But it couldn’t shred PET bottles and kept on jamming. So we changed to 1:80 (works just well) with forward-reverse switch. [how should I post video though?]

And we thought it’s good if we have some auto-stop mechanism, just in case the machines jam and stop. So we added an optical encoder and did some programming. We have 3 relays in total (1 SSR for main power, 2 mechanical relays for forward-backward control). The [yet-to-be-finished] programme would stop any power to these relays and halt the motor.

wkhs

starter

08/05/2017 at 14:39

2. Frame

Never trust aluminium. Never, ever.

A strong and well-built Al frame can easily support the weight of motor, gearbox and the shredder (or yourself). It’s tempting to use them (esp for those who built 3D printers with 2020 Al profiles). But Al is definitely not for the torsion of your monstrous motor!

Whenever the motor tries hard shredding tough things, either the aluminium bends or the gearbox-shredder combo will slide away from each other (depneds on how tight you have tighten the screws and whether your profile is slotted to allow sliding). I couldn’t explain on this observation further (sorry I am a amateur :D).

May be there are better cross sections for the profiles that can do the job but I suggest using steel for precious plastic machines in mechanical parts. (Yes we don’t machine SS in our labs normally. So we either purchased or used the thickest block of Al to make the parts for the injector).

Bring home msg 3: Never trust aluminium. Never, ever.

wkhs

starter

08/05/2017 at 14:26

So I’m gonna start with the shredder first. We started designing the electronics back in Dec last year, and finished the whole thing functional in Mar. It’s hard but great fun too!

1. Laser-cut parts
We just sent out all the files to a manufacturer in Mainland, China. They offered us it done in 150-200 USD (transportation fee inclusive).

It was a great deal until I found they have the wrong thickness… yes it’s 5.43mm not 6mm.

You see that machining? It’s a mechanical engineerer from a lab helping us out to make some extra spacers to make up for the thickness gap. Then we burnt out two drill bits… (weird moment when you see a slot in the drill bit because the steel was too hard that it milled a track on it!)

Bring home msg 1: make sure you know the tolerance before placing orders (until we have parametric designs like OpenSCAD).

Bring home msg 2: buy G-O-O-D drill bits.

wkhs

starter

05/04/2017 at 19:59

It depends on the heaters you use.

I use 4 x 300W heaters on 220V. So it draws 5.5A during normal operations. But to play safe I just buy a FOTEK-40A (capable of 40A) because there are Chinese counterfeit products.

wkhs

starter

02/04/2017 at 06:25

Hi @allie, @gaby1603 and @icybaby, we have some progress in building shredder (done) and injector (testing).

We have also started a FB page here: https://www.facebook.com/preciousplasticcuhk/

wkhs

starter

27/02/2017 at 15:59

[Updates] putting into electronic box
(ignore my breakfast coupons)

wkhs

starter

27/02/2017 at 15:55

[Updates] Connecting wires and enhancing current capacity with bare copper wires

wkhs

starter

26/02/2017 at 07:26

Thanks for tagging.

Hi @allie, this is William. We are a team of 5 (+2 technicians) in CUHK. Currently we are building a shredder and a injection machine. Tell me if you want to know more~

wkhs

starter

13/02/2017 at 04:59

I would love to. But my current version is not yet updated with my improvisation (ie where I corrected drawing faults with jumping wires). I was trying to find if anyone can help me double check on my work. But…I don’t see many enthusiasts in electronics here..

If you’re fine with the current faults, I can send you a copy in advance

wkhs

starter

17/11/2016 at 05:17

As far as I could remember, ~30mm inner diameter (ID) pipe is used for injection. Suppose you have just 30cm length for the column, the pipe has a capacity of 850cm^3.

For your lampshade, calculate the volume using the formula (8) in http://mathworld.wolfram.com/ConicalFrustum.html. I used volume of (R1,R2,h)=(10,8,10) subtracted from the volume of (9.4,7.4,10) [=3mm shell thinkness]. Then the volume is 2555-2227=328cm^3.

So its ok to inject the volume. For weight, the screw thread is likely to be DN28/DN35, they are strong. Total weight of all plastic that can be holded in the column is merely 850 * density = 1.19kg for PET (probably the heaviest you will recycle)

wkhs

starter

08/11/2016 at 15:33

It is probably dangerous to switch electronic boards by plugging it back and forth. But it is possible and cost effective to design a 4-in-1 board (ie one board can be adapted to all four machines, differing only the firmware to be flashed). My latest circuit board is injection + shredder. By then you need 4 identical boards.

wkhs

starter

18/10/2016 at 16:02

However, this PCB is one-sided and has no silkscreen. I chose the wrong footprint for IDC-10P. And the manufacturer modified my signature, strangely.

Probably needs some revisions…

wkhs

starter

16/10/2016 at 11:45

How “detailed”? I’ve seen people casting Al out of 3D-printed PLA. But quality of the resulting mold is limited to the printing quality.

But that is cheap.

wkhs

starter

10/10/2016 at 13:58

@ramdhan2805 I live in Hong Kong (which is far from most industries in China). A delivery company (which I often use its service) gave me a rough quotation:
100RMB (first 0.5kg) + 70RMB/kg * 13kg (subsequent kg, rounded up) = 1010 RMB ~ 150 EUR
The price is for US/UK/France/Ger/Ita/Japan/Thai/Canda… etc.

I might be able to help you guys place orders. The producers don’t seem to communicate in English well I’m afarid

Sadly they don’t ship to Indonesia apparently… I saw another company of similar pricing and can ship to Indonesia.

wkhs

starter

09/10/2016 at 19:16

@ramdhan2805 Probably <200eur. But I have not sure what sort of company does that.

wkhs

starter

09/10/2016 at 03:42

Here in China it only costs 110EUR for all laser cut parts (excluding hopper)…

wkhs

starter

25/09/2016 at 05:57

1: Thanks @davehakkens! How about the shredder parts? It’s not a must to weld, I guess? (Except, well, the sieve perhaps…?)

2a: I have found a specialized coupler for these “keys”. See the attached for the nomenclature

2b: I got an answer from the excellent stackexchange.

wkhs

starter

24/09/2016 at 09:58

How does this compare with arc welding?