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Super Glue Gun 04: Hold Me Closer, ATTiny -- Episode 290

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element14's The Ben Heck Show

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Super Glue Gun
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Previously, the team worked on the triac to control the hot end, extruding glue through the hot end, and finding the best DC motor and drive gear to push the glue to the hot end. In this episode, the team is going to make another test rig using a slightly faster DC gear motor and get started on programming the ATtiny microcontroller that will drive everything in the glue gun.

 

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Ben finds a DC motor with the same form factor as the one he used before, but its 50 rpm instead of 3 rpm. The mounting is different so he goes into Autodesk Fusion 360 to design a 3D Printed mount.  Ben exports his design as a DXF (Drawing Exchange Format) so he can cut a paper pattern on the laser, make sure the holes are correct, and once that done he can print it. The paper pattern is way off so it was good thing he started this way than with a 3D print. It takes many tests to get the right dimensions.

After 3D the part and measuring the distance, the latest revision to the motor mount is a little loose so another revision is made on the 3D printed part. Once the part is dialed in, they’re going to take the glue stick and get its center point, and use that to make their guide shaft. That will get them close enough to do a test with the hot end again. 50 rpm motor gives them a lot more speed than the 3 rpm motor, however more speed means less torque so hopefully it has enough power to push the glue through the hot end. Once it seems to work, it’s time to make the next revision to the 3D printed part so they can push it through the hot end.

Ben has a new board he made for ATtiny development.  It’s got a larger socket on it for the ATtiny20.  He’s also working on a sub socket for the ATtiny4 to give him a couple of options for what he can use. The ATtiny20, is the most likely candidate for use with the Super Glue Gun, as it gives him 6 IO. The board gives him a way to program these little chips as well, especially as they use the TPI – Tiny Programming Interface – instead of the SPI (Serial Peripheral Interface).  Once the board is wired up they can get to work on some code.

Ben goes on Atmel Studio to do some programming for various ATtiny chips. AtmelStudio is based off of VisualStudio and is well integrated with Atmel microcontrollers. Ben goes over logic for programming an ATtiny chip. The PWM pin is set to be an output. On this a 1 is an output and a 0 is an input.  He sets up a timer to drive the PWM. Ben does all the code in AtmelStudio, so they can be develop it on a low level, have a file that’s easy to program, and they can make the device.

An H-bridge is a circuit for reversing the direction of a motor. Ben explores making his own H-bridge on the PCB. He looks for some MOSFETs to make a full H-bridge.  He interested in finding out what that would cost vs. a dedicated, integrated circuit. He goes with a Duel MOSFET, N and P Channel.  Once he finds some power MOSFETs to make his own H-bridge, he’ll wire it up manually so he knows exactly what’s going on and can low level control it with a microcontroller.  They will also need to figure out auto stand that kicks out. They could possibly use a servo, use a timer on the ATtiny and have some PWM running at 50 hertz. For now he’s looking for the cheapest way to possibly drive a motor.

Disclaimer

  • Great episode with lots of detail on how you go about bringing an idea to product.

     

    DAB

  • Liked the wrap-up discussion of design alternatives and reasons you decided for or against.

     

    Liked that Ben is considering costs early and looking for simplest/leanest parts alternatives.

     

    Liked the bottom of the screen notes to define tech acronyms.

     

    Liked that a faster motor was used.  You'll need if for factory packaging applications.  Have you decided what applications the glue gun can support?  You can see various types here:  https://www.gluegun.com/

     

    Not sure why it took so many attempts on paper to get the right positioning of the motor screws.  In the past, Ben took a photo with his camera and resized it to actual dimensions in CAD system.  I thought that was very efficient.  Would this method had worked better here?

     

    If you run the motor too fast, does the glue not melt fast enough and cause slipping/jamming?  The temperature of the heater chamber may not be able to be raised fast enough to keep up with the motor.  There's a finite amount of pre-melted glue in the heater chamber.  Once that is pushed out, the cold glue needs time to melt.  So if the motor has not been used in a few minutes, the glue in the chamber is all melted and can be pushed out quickly.  But if you continue beyond this, the output rate cannot be maintained without additional heat.  So the motor speed may need to be reduced in the software for continuous feeds and keep track how long the motor has not been used so it knows it can blast out fast for a short duration.  Additionally, the heater temperature could be regulated depending on the motor speed.