Printing a better world – one bit of plastic at a time

I’ve been working on a robotics project (off and on) for the past 5 years, specifically this little guy here. It has proven to be quite a challenge because the animators that designed WALL-E weren’t really concerned with silly details like the laws of physics or that law that says you can’t be in two places at once. Some of WALL-E’s movements and his appendage/apparatus juxtapositions would require TARDIS-like capabilities to achieve. Undaunted, I launched headlong into my pet project.

Being a long-time R/C model airplane enthusiast, I naturally started fabricating WALL-E using model airplane building techniques; balsawood, plywood and glue. Some rust paint and metal effects, then throw in a bunch of servos and linkages, and this is the result:

Ta-daa! as WALL-E would say. The completed head assembly is about 35cm long and weighs nearly 2Kg. Besides the six servos that control his eyebrows, head droop, head nod and turn the head contains a PIR motion sensor and milliwatt laser. I figured the laser would be great fun for driving the family cat crazy.

Of course I had to be able to move the head up and down, just like the “real thing” but fabricating the lift mechanism and finding a servo powerful enough to move the whole thing, would prove to be a challenge so I decided to look at 3D printed parts as an alternative. But hold on thar, baba Looey! It turns out that 3D printing comes with its own bag of fiddley, finicky, hair-frazzling problems – you can’t just plug these things in download a model and expect your print to come out sparkly and shiny. In this blog I’ll recount some of my experiences with my first 3D printer – a Creality Ender 5 Pro.

While this printer is very capable for the price, it does have some shortcomings, like:

  1. no bed-leveler. While there are add-on kits available for relatively cheap, this is something that even lower-cost printers like the MonoPrice MP10 mini offer as standard equipment.
  2. no out-of-filament sensor. Come on! This is almost like buying a car with brakes as optional equipment. Even the cheap-o MonoPrice printer has this as standard.
  3. a cable-bundle-keeper-out-of-the-way-thingie. OK, this just a minor complaint that’s easily fixed with a piece of coat hanger wire, but still…

While very annoying, these are all things I can work around. What really bugged me was the poor quality prints I was getting because of:

  1. wobbly print bed
  2. filament clogging at the hot end
  3. filament getting tangled and falling off the spool

I also wanted to be able to monitor the print using Octoprint and a webcam. Unfortunately, printing directly from Octoprint is error prone for long-running jobs because of sporadic communication errors. More on this in a later blog post…

To fix my first problem (wobbly print bed) I decided to add a second leadscrew and linear slides directly across from the first set, like this:

First, the electronics box had to be moved back a smidge to make room for the lead screw pillow block and slide rail supports. Next, I used a 2-inch wide piece of aluminum bar stock drilled and screwed directly to the print bed carriage. This essentially extends the length of the carriage so that the slide blocks and lead screw could be attached – here’s a view from underneath the print bed:

A set of GT2 pulleys and belt loop driven by the z-axis stepper motor fixed my wobbly bed. Note the presence of the belt tightener pulley because I couldn’t find a belt loop the exact size needed.

The next enhancement was to add a direct-drive filament feeder. The old Bowden tube arrangement was OK, but I wanted to play around with TPU (flexible plastic) which almost requires a feeder that can retract the filament instantly. It also reduces clogging and the number of times you have to burn your fingers trying to clean out molten plastic from the hot end.

This meant that the filament spool holder had to be relocated. The only appropriate spot I could find was at the back of the frame, here:

This arrangement worked well, until the filament started coming off the spool and fouling up the works. To fix this, I made a filament guide out of a piece of 1/2 inch aluminum bar. This is the L-shaped thingie in the picture above. It has a slot to limit the side-to-side filament movement and seems to work quite well.

I hope this helped – please leave comments or questions below.

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