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  • Author Author: dubbie
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HoloPiBot #5 : Some Movement Has Been Achieved

dubbie

In my unofficial attempt at the Picasso Design Challenge I have made some progress and I now have two motor units fixed to the display screen. I did have some problems in drilling the acrylic sheet used to make the holder for the display as it is very brittle. I cracked both of the back sheets that make up the four layer holder, in three different places. I thought I had placed the sheets onto a stable flat surface before I started drilling, but unfortunately I forgot that I was resting the display on the heads of the four screws used to hold it all together, so of course when drilling between two of these supporting screw heads the acrylic would bend slightly. When the drill broke through the bottom of the second sheet, the bending was enough to promote crack growth so it kept snapping. It took me three attempts to work this out, but afterwards I managed to avoid any further snapping or cracks. It is not too much of a problem functionally as I have now glued everything together. It is just irritating - I should know better.

 

I plan to add four motor units to the display, one at each corner, but unfortunately I did not have enough motors so I had to order motor. While I was waiting for the extra motors to come I decided to just 3D print some supports for the two corners that did not have motor. I managed one and then my 3D printer also choose this time to run out of plastic spool so the video below just shows two motors and one support.

 

 

The system is just about working and with the two step motors powered to move forward the whole system does actually move. The step motors I used are small but they are also incredibly low power and have virtually no turning torque what so ever. They are just feeble. With only one motor if I added the battery pack to the display it just stopped moving. With two motor units it just about keeps going. I am hoping that with four units it will be acceptable. The system is moving slowly at the moment but that is the plan, so that it can display a magnified image of the Picasso painting that it is covering. Once I have more spool for my 3D printer and four motor units added I will also see about implementing the ability to turn as well as move forward.

 

 

The Raspberry Pi 3B+ starter kit and the camera V2 have been ordered so I will also soon (he said optimistically) be able to start displaying images on the display. Then it will be almost finished!

 

Dubbie

  • in reply to dubbie

    Thank you Dubbie,

     

    about the 3D printing technique, I will describe it with some images in my next post on month of the robots.

     

    Enrico

  • in reply to balearicdynamics

    Enrico,

     

    Another good tip. I will definitely try this one.

     

    I might also try drilling a smaller hole first and then drilling that out to the required size.

     

    Dubbie

  • in reply to balearicdynamics

    Enrico,

     

    I had noticed that just before breaking through the acrylic there was increased vibration. Your tip on using the pillar drill is a good one so I will try that if I have to drill acrylic again.

     

    Also, your tip on making a shaft hole slightly smaller and then heating the axle is also a good tip and I will investigate that further as I want to 3D print some larger but thin wheels (these are better for HoloPiBot as they reduce the friction when turning. This reduced friction is not a problem when moving forward as it is four wheel drive.). There are existing larger thin wheels but they seem to have a circular shaft rather than the double flat on the stepper motors. There is also room to put an Allen screw or similar into the side of the 3D printed part so I might try that as well.

     

    Thanks for these very good ideas.

     

    Dubbie

  • in reply to balearicdynamics

    UPDATE

     

    I forgot, sorry but after I discovered Perspex it is more than two years I never bought acrylic stuff. Without a column drill, you can use large (5 cm) paper adhesive tape on both sides where you should drill or saw. This absorbs the vibrations and with a minimum of caution you avoid breaking the material.

     

    Enrico

  • in reply to dubbie

    If –as you say– you need sure use this material, to drill acrylic there is a technique. Better if you use a drill column, you should put the tool rotating ad high speed to produce the smallest waste as possible, and move down the drill point for very short periods, like a punching operation. This avoids that the acrylic becomes heat. The problem is just his; when the hole around becomes heat, acrylic tends to melt with the drill tool, and the small block of plastic lock the acrylic around, create horizontal vibrations that open and breaks.

     

    About the shaft, I should say that 5 mm is not only, is very big image !!! I have managed 3 mm shaft with 3D printed parts. There are two techniques. The first is to make the hole a bit (0.1 - 0.2 mm) smaller, then with hot air (or the soldering iron if you haven't a hot air source) heat the metal shaft to about 80 DEG for a short period and push the plastic pulley inside. It melts a while then solidify without deforming.

     

    If you have more space, the most reliable alternative is using a small Allen screw and a bolt But if I don't see the design I can't tell more.

     

    Enrico