12/22/2016 at 15:17 •
Lets start from the ground up, the base. The original was made out of 8mm MDF because I wanted it to be a stable platform for the cake to move on. It certainly was stable but 8mm was total overkill.
This version will use 3mm MDF with 3D printed elements (not pictured) to strengthen the high stress area at the rear. Using 3mm MDF allows us to use affordable laser cutting services to have the pieces cut out and delivered cheaply.
I consider using 3D printing for the base but my 3D printer on has a 150x150cm (6x6") base. I would need to print in 6 different parts and screw them together and that all seemed a bit clunky to me.
MDF has a nice finish if you want to paint it (in food safe water colors of course) or will happily take an plastic adhesive-backed covering like the original has.
01/02/2017 at 07:14 •
Where the original cake had 2 motors, the new cake will have only one.
This time instead of an expensive stepper motor I want to use a DC motor with a leadscrew (pictured below) because they are cheap ($5 from Ebay) and the control electronics, a DC motor controller shield, is also affordably prices on eBay.
The Cake, including icing, will weight an estimated 1.6kg (3.5lbs). But because of the leverage of the lifting arm the motor will have to move 3x that, 4.8kg (10.5lbs)
I hope to use no more than 6 AA batteries to power the electronic but there is a bit of trial and error to come after my parts arrive in a few weeks.
Naturally I will create a BOM (Bill of Materials) as the project progresses which will include a list of all the final electronics and links of where to buy them.
01/15/2017 at 01:32 •
Recently I have been preparing the body parts for printing and assembly. Adding tolerances (gaps between parts) , beveling (removing square edges for cleaner prints) and adding little pegs with holes so the whole thing can be assembled with the same sized small screws.
I'm just waiting on some red and blue PLA filament to arrive to print some test parts and check all my guesses.
As we are creating something that will interact with food we need to be food safe. PLA is considered food safe (It's made from corn starch) and we will use food-safe petrolium jelly as a lubricant in all the joints.
01/26/2017 at 23:59 •
Two rolls of lovely blue and red ESun PLA filament arrived yesterday from hobbyking.com
I'm excited to get started printing but to avoid wasting time or filament I started with a test print (see montage pic), because there are moving parts it's important to get the fit right.
I'm printing on a lulzbot mini using default medium speed settings profile. I'm aware not all 3D printers are as good as the Mini so I am making the gaps between pin and barrel wider than I normal do. Additionally all the holes sizes are common metric drill bit sides (namely 2.5, 6 and 10mm) so if your printer gets over excited you can just drill the hole to clean them up.
In the original cake I used M3 bolts which are more at home in metal than plastic. This time I am using common hardware wood screws. Only two types: 25mm to securely join the feet to the base and 9mm everywhere else.
The tests print gave me the feedback I need so I can now start printing and begin the print-fail-feedback-repeat cycle until I am happy with the 3D models, then I will publish the stl's here on hackaday.
02/09/2017 at 00:05 •
This week I received my Laser cut base from Ponoko. I think Ponoko will be my go-to online shop for Laser cut from now on. I was really chuffed with their service: functional and easy to use web site app, automated price quotes and fast turn around time. Plus $20 off my first order.. niiice.
The only trade off for this efficiency is that they use set sheet/template sizes so I had to shrink the bases design a little too get it to fit in the most affordable template.
A little bit of masking tape and wood glue and the base is now complete.
02/14/2017 at 14:59 •
I have started 3D printing and so far, so good. There are are many pieces to print so whilst that is happening I have started on the actuation design. Using a gearmotor, leadscrew (m4 thread rod) and micro switched for end-stops.
03/25/2017 at 13:58 •
The first run of the printing is done and I'm really happy with the proportions and the standing motions some of parts aren't playing as well together.
In my experience with 3D modelling and printing this is to be expected. 3D modeling is great for designing the parts but as for interactions, how parts move with each other, there is little substitute for the real thing. So I have a few refinements to make, mostly on how the arms open and shut and how the head is raised and lowered.
In the picture you can see the little lead and steel weights I am using as stand-ins for the cake to make sure the motor and batteries are up the the task.
Also pictured is the switch (top-left corner) that I am using to activate the open and down motion for testing. Currently it is a simple switch, no Arduino yet. I am using 6AA batteries for about 8v of power and so far this seems to be enough juice to lift the frame with 900 grams of weight in 6 seconds.
As soon as I am happy I will post a video and the STLs soon after.
03/28/2017 at 13:53 •