Colour sorting machine for Lego

The drum scoops are redesigned to be smaller so that fewer pieces are dropped each time. Also I've gone back to six scoops instead of twelve, which leaves gaps between the scoops which is useful when there are only a few bricks left in the drum. 

Here are just a few of the scoop designs I've tried along the way: 

Also, after much coding, a bit of soldering, and the design and print of a case, the TOUCH CONTROLLER! 

So it's been a while since the last log, and the machine has had many outings to school STEM events and the like. It has mostly worked really well, and got lots of interest and sparked lots of discussion - which was the whole point.

However, I've had some ideas for improvements. Some of those were implemented today:

- swapped out the vibrator motor for a larger one (a "280") since the original one got pretty warm and wore out too fast.

- added control of the stepper driver's nENABLE pin so that the stepper current can be switched off between moves to save power and stop it getting too hot. I think the shaft was previously getting so hot the 3D-printed PLA part attached to it actually melted slightly.

- added serial commands to start/stop the machine, adjust motor speeds, and read out a count of bricks in each bin.

The last item is there so that in the near future I can put together a touch-screen controller with a real-time display of brick counts, plus the option to tweak the speeds, stop it if there's a problem, etc. Watch this space...

A bit more tidying up, addition of a hopper and chute to load Legos into the drum, some fine tuning of the angles and software and it's done!

It's not perfect but it is really fun to watch. The main remaining issue is that the scoops inside the drum sometimes pick up quite a few pieces, which then overwhelm the vibe feeder and they end up tailgating each other past the sensor. Something to tweak later. I'd also like to add a touchscreen with start/stop buttons and some readouts of brick counts, speeds, etc. Other ideas in the comments please! 

First time putting together all the parts:

I've chopped up something like 2.5metres of 2020 aluminium extrusion and turned it into a more permanent, more rigid frame for the drum feeder, vibration feeder and sensor head:

The drum is belt driven from a DC motor/reducer gearbox running at about 200rpm. I needn't have worried about the belt wandering off the drum - it's absolutely fine, without any need for additional guides or track to keep it centred. 

Everything's adjustable - angles, clearances, etc. - so the next steps are to do some tuning to get it feeding reliably and quickly, before finally integrating it with the diverter and output bins.

The drum feeder is looking good now. After a bit of trial and error making paddles/scoops from card I've committed to a 3D printed design that works well enough for a first attempt. Physically positioning all the various parts was getting really tricky using the wooden lash-up so have also started the 'finished' build in 2020 profile and M5 fittings.

I think I'll try a belt-drive to power it, from a DC motor and reducing gearbox. Only problem with a belt is that the drum has a slight draft to the sides, meaning that the belt will undoubtedly tend to wander off...

So after a long break to get some other projects finished, I'm back to the Lego sorter and its drum feeder. 

It may look like a food container, sat on some rollers, and with a hole in the lid, but it's much more than that! Actually, not really. That's exactly what it is.

Using a bench supply to control the current (and therefore speed/vibration frequency) of the vibrating feeder was getting a bit annoying, so I finally took the plunge and added an H-bridge driver and PWM control. Initially I tried an L9110S-based module (very cheap on the 'bay) but it wasn't up to it and kept overheating. Plus it doesn't support 'coasting' so ended up being quite noisy and inefficient.

I swapped it out for an L298N-based module (almost as cheap) which is much better. By driving the ENABLE line with PWM, and holding the IN1/IN2 inputs H/L for fixed direction, it's possible to employ coasting, which keeps the motor happier.

However, the Arduino's built in PWM frequency (977Hz) is very noisy, and changing the prescaler to get other values is no better (3.9kHz is also noisy, 31kHz is too fast for the driver). So ended up with a bit of code to set it at about 15kHz, which is perfect. Pretty much silent (to my deaf ears anyway) but with smooth power control and no overheating.

Plus, the L298N has dual outputs, so I've still got a spare channel I can use to control the drum feeder's motor, when I get to that stage.

After quite a lot of trial and error on the feeder, I've settled on a design where one end is a hinge, forcing the vibrating motion to be confined to up-down only, and with low amplitude at the hinge end, and a large amplitude at the free end. It seems to work well at separating parts as long as there aren't too many at once:

Obvs this is a dirty quick prototype using scraps lying around, I'll do a neat version one day out of profile aluminium...