Looking for Raspberry Pi HAT/Servo/Sensor recommendations

As the saying goes “Long time listener, first time caller”…

I’m working on a project to separate, identify and sort Lego parts from a source container of mixed parts. I’m leveraging previous projects that have been posted online (such as Daniel West’s Universal Lego Sorter link)in terms of the mechanics, and have separated the design into stages that will each need motors &/or sensors. The current plan is to have a Raspberry Pi CM4/Carrier board combo run as the core of the project.

Stage 1: Source bin and feeder to stage 2
My current thinking is to use a linear actuator to push one side of an angled container whilst a vibrating motor shakes the contents to reduce friction (based on a volume of particles displaying liquid like properties when vibrations are passed through, e.g. sand). Output with be pushing a small quantity of parts into stage 2 for physical separation. A sensor in stage 2 will act as one of a series of on/ff switches for stage 1

Stage 2: Separator.
A v-shaped channel, with fixed support at the exit end, suspended via springs at the opposite end, using vibration to shake pieces down and onto a conveyor (Stage 3). I think the way to go is to use a break beam sensor to detect the drop of this section and send an off signal to the motors in the previous. Another break beam sensor at the exit end, signalling a stop for the vibrating motors in the stage 2, and activating stage 3.

Stage 3: Identification
I’m thinking a conveyor through a camera box, exiting to a funnel with a variable position exit chute.
Another 2 break beam sensors (one to detect a part in the camera box, another to detect it’s exit into the output chute, and a Raspberry Pi camera to capture an image for identification (this will be sent over network using a queuing broker to a machine learning server).

Once the ID-query-response returns a result (either matching sort parameters or default null), restarts the conveyor to eject the part.

Stage 4: Sort Output
Here I’m thinking a stepper motor to control an output chute by rotating through 180 degrees into a series of output bins. A final break beam sensor in the output chute to signal Stage 2 to output another part into the system.

From the Raspberry Pi out, here’s what I think I need:

  1. Motor Control Hat (or multiple, stackable) capable of controlling all the motors, ideally with software libraries for Python/Linux
  2. Motors:
    Linear actuator
    Vibrating motor x 2 (perhaps 4? if paired would be more effective)
    Conveyor motor (standard servo or DC motor)
    Stepper motor
  3. Sensors:
    Break beam sensors x 4, or alternative. Support software libraries in the same language as the motors would be ideal to keep things as simple as possible
    R-Pi CSi connected camera/lens

Based off Daniel’s project, I plan on using a Tensor Flow convolutional neural network, with MQTT brokering between the AI engine and the Raspberry Pi.

Any thoughts or advice on this, especially around the Pi controlled hardware, is appreciated.


Hi Troy,

Welcome to the forum :slight_smile:

I hadn’t seen the video of Daniel West’s build, it’s very impressive and looks to be a solid design to base your project on.
Overall your game plan sounds sensible to me, I can’t see any major issues that might come up, every build will have little surprises though.

For any complex project I work on I like to have a little sanity check for each stage testing “Is there a simpler way to do this?” with either less parts or less complexity. The only point I can think of currently is it might be worth considering servo motors for the stage 4 sort output rather than stepper motors.
Either should be able to achieve the aim of 180 degree positioning, but steppers will require a dedicated stepper driver whereas you might find a servo you can control directly from the Pi, then only need a DC power supply rail to support it.

The big picture plan looks good. I say go for it with stage 1 and once that is functioning well enough begin the next stage. Lessons learned in stage 1 might allow you to change course before you have committed the budget to something for all 4 stages if hiccups arise.

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