15. Mechanical design¶
|This weeks design|
This weeks assignment is making a machine. Other then the previous assignments we work together to make a machine. We have the freedom in designing whatever machine we would like but with three requirements. The machine need to have a mechanism. A system of part working together in a machine. Need actuation: the action of causing a machine or device to operate and automation. The technology by which a process or procedure is performed with minimal human assistance.
As a group we focused on brainstorming for potential projects. A lot of different ideas came to mind. A grinder machinary to avoid the use of dogbones on the cnc machine, a table vacuum cleaner, etc. In the end we decided to make a visual representation of the booking system we have at the Waag. The machine whil read the api of the online bookingsystem and with the use of marbles you are able to see which hours the machine is reserved. Now the type of machine was clear we had to come up with a design. There are many ways of making this machine. We all sketched our own ideas what we had about the looks of the machine. My idea was to make a horizontal calender where you drop the marbles on the right time of reservation.
Brainstorming about calender, mine is bottom right
My group member preferred to make a more complex machine where the machine drop in vertical and each individual marble get knocked of by a servo motor. And when the marbles are kicked of the will go to the top of the machine using a movable stairway. It is a hard machine to make but when we succeed it will be a fun machine to watch.
different sketches for design mechanism
We divided the task between the four of us. Joey is responsible for the row where the marble indicate the time table of the machines. Each individual marble has a servo motor to knock the marble out of place. Joey
*joey design so far * Micky will make the frame of the machine where the different parts will be locked in. Micky
Micky build the frame
Anne will make the marble collector. This will be place above the time table. It collects the marbles and put them in place. Anne
rail and construction by anne
I will be concentrated in returning the marbles on top of the machine. Will research different method in which mechanism to use.
Playing around with carton to test ideas.¶
First we played around with carton to see the mechanisms in real life and test some concepts. Since we based it on a simple sketch the dimensions where not fitting yet. We all focused on our individual parts to see if the concept could work.
This week is foccused on making a machine construction with all the students of the fablab Amsterdam. After some brainstorming we decided to make a visual representation of the machine booking system here available at the waag. We have a few mechanisms that should work together. My first focus is making a stairway to move the marbles from the bottom to the top of the machine.
I liked the visual way of how the marble stairs work and decided i would give it a try to make. When looking at the design it looked remarkable easy but i assumed it was going to be quite a challenge to make the marble run without them falling. The marble we purchase are 16 mm width. I decided to go for the 18 mm wood for the stairways. The example on you tube works perfect but the dimensions are much smaller.
Inspiration how to make stairs
In this video you can see the mechanism work made out of solid wood. Only one stairway is moving and transfer the marble to the next stair. I want to simulate this mechanism but in a greater dimension with the use of a big stepper motor.
*Playing with the mechanism *
The joints function in fusion 360 is very useful when designing multiple parts thats should work together. With this option you can move different object together and replicate the movement. Fusion does not allow you to use bodies with the joint function. First you have to change the object to a component.
Making a component
My first effort to make a marble stairs finished when looking the movement of the two stairs using the joints function. The sairs are separated by a circle combining the twoin a movement. This would not work because of a gap between the stairs and it was tricky to connect a stepper motor to the device.
Simulate the movement using joints
I was sceptical in making the design so i was also looking for alternative when the stairway would not work. Here i made a quick design for a wheel to bring the marbles up to the top of the machine. I realise quick the amount of material needed to make a wheel this big. But always good to have some alternatives.
Trying some alternatives
On friday our group can together and i was motivated to get a stairway before the weekend so i could focus on the mechanism itself. I designed a larger version so the marbles could reach the top quicker. I calculated a 8 cm step per movement. When i was preparing the lasercutter i noticed i had not the material needed to make my initial idea. (which was bad btw.. ) I designed the stairs so it would fit the board available in 18 mm.
Not so happy as i appear on the picture
The result was a useless heavy stairs what would cost me tremendous handwork to make it work. Most likely still to heavy. Lesson learned. Never rush when your idea is not worked out. Back to the drawing board
My first attempt was a bit of a failure. I should have take more time to think about the mechanism before going to start. I was to eager to move on to the next stage for making the movement mechanism. Over the weekend i redesigned my stairs in a way i though it might work. The problem with the previous is besides its way to heavy it would take allot of manual hand labor to get the holes perfect for the marbles to go in and out. I wanted to demonstrate the machine you can make using the machines.
Many alternatives in mind but still want to make a stairway that functions. So next plan was to redesign the stairs so the marble would stay in place when moving step to step. I thought i might be able to laser cut two sides for each stair that function as a rails. I made the rails with a minimal degree of angle so that the marble would run to the end and then slide to the next stairs.
Every time when design in fusion i learn better ways in designing. Mostly because of my mistakes. I needed two sides for the stairs. I first made the stairs itself and then separate the sketch. Later on i wanted to make the slots to fit it together. I would have save time if i would first have the focus on the different slots and the separate the piece to its own design.
A over constrained design in twofold
For every stair i designed two sides. Both with a angle of 2 degree to make the marble move.
A minimal angle to make the balls roll
The other side have a small edge to make the marble run to the other side.
Design of the stairs both sides
Th marble should go out of the stair at the end and the other stair is in mirror. This way the marble should move up the stair.
Before making the complete stair i started making test. My first priority was the design being press fit. Here i looked back at week 4 (computer controlled cutting) to determine the offset i should use for the slots.
The test we made with soft poplarwood
I did some testing and now wood is the same thickness. So i had to run some test before i had a nice press fit construction.
A bunch of testcases before i was happy with the result
Now it was time to test my design. I first wanted to make a test with a few stairs to check the mechanism and if my design worked in real life. Turned out it did not. The marble did move till the end but did not fall of the edge. Did not take the mass of the centre in account. I had to rethink how to safe this design and came up with a small piece centred to guide the marble out.
between the part you see the pieces to guide the marble
When this worked i dared to make the real size stairs.
Puzzle to assemble stairs one
To make a stable base for the stairs i used a thick piece of wood and drilled holes on the right dimensions. The holes on the stairs in my design are 20 cm apart. First i took a offset of 8 mm of the side and draw a line. The stairs are each 16 mm width and i want the stairs located at the side of the base. The next line i drew 16 mm after. This way the stairs will be aligned perfect. The second row i drew 20 mm to the right. Each individual stairs is 4 cm width. This way the two stairs will be placed so the marbles can run to the other stairs.
Drilling hole to mount the stairs
For a mechanism to move the stairway i intend to use a stepper motor. I need to find a connection between the stairs and the stepper motor.
this stepper has a connection
This stepper has already a connection mounted on it. measured the connection point to design a fitting connection to fit. I design the shape by looking and measuring. I used a minimal offset of 0.1 mm to make it fit. I did a few test 3d prints to get the perfect shape that fits with no friction in the design.
When i found the correct dimension i made a wheel of 60 mm with a inner circle of 45 mm. On the inner circle i drew a circle of 3 mm to attach in a later stadium bolts on. This way the stairs will move up and down 45 mm. I decide to give a minimal ofset so i can be sure the marble has space to move to the other stairs. It has to cover a distance of 40 mm. With 5 mm ofset the stairs doesnot have to bbe perfect alligned.
Design to fit the stepper
The wheel will encounter much force from moving the stairs up and down so i changed some settings in cura to make the print more endurable. In setting i gave it a outside solid layer of 1 mm and a cubic infill which is a strong infill method. Further i used the high print quality of .1mm per layer.
Using 3d print to make the wheel
As a temporary solution i made connection pieces to connect the metal with the slider. on side the slide fits in press fit. The other side a hollow tube to slide through the hole.
The next part goes on top of the hollow tube. The other side a Barr thats is mounted tight that goes to the holes of the stairway.This way i can create a steady moving stairs that only moves up and down and driven by by the stepper
Next picture shows the different parts mounted. Here i still use wood for the purpose. Final design will have metal bars.
connecting the parts for sliding
when all pieces were connected i felt steady enough to be used. Next week we will continue with the machine week and put the stairs to the test. It looks promising so far.
result so far
What i learned and what went wrong.¶
The biggest thing i learned from this assignment was not to be to eager to start without having a clear idea of how to tackle the challenge. That was the reason i lost time and material making something without a well thought plan. I like the teamwork with my fellow students. They all take there part serious and we were willing to help each other with the assignment. One thing i would like to see different next time is first ready looking at the challenges of the machine. Having a clear understanding in what to archive and how the different part will fit together.