Introduction: Simplified Engine Cut-away
As an Automotive university student I have chosen FabLab Making as an elective course. I'm planning to make a very simplified combustion (a.k.a. otto-) engine cut-away for decorative purposes.
In this course are a few demands on the making of the product:
- A hinge of some sort has to be implemented.
- An (simple) electrical circuit has to be used to for example drive a motor, light, etc.
- The use of at least three machines is mandatory: a 3D printer, a lasercutter and an electric machine of choice.
All my digital drawings are included which also contains the drawings to put it together before making it. So you can assemble the parts in Autodesk Inventor or any other programs that can open .dwg and .ipt files.
A few 2D drawings are also included which can be used for a lasercutter. Be aware of converting these files into a laser cutter compatible extension because it can occur that de drawings will contain double vector lines due to the converting proces.
Step 1: Creating an Idea, Sketch, Boundaries and Planning
As a first step you have to brainstorm about what to make. At first I was thinking about making a brushless gimbal for my GoPro. As a snowboarder I like to film my buddies but I'm not able to make stable footage as snow isn't always smooth ( and I'm not that good in snowboarding to keep the GoPro completely still).
One of the criteria for this elective course is originality on which a brushless gimbal is not at all. A great number of (3D printed) gimbals already exist. So I chose to make a simplified engine cutaway which shows how the combustion (a.k.a. Otto-)engine works.
If you take a look at the image above, I made a sketch. Please do keep in mind it's just a first sketch so the dimensions and proportions are not correct.
The most parts will be laser cut and 3D printed because these parts are quite difficult to make otherwise within the CityLab R'dam.
- In the cylinder you have the round piston and ofcourse the cylinder itself. These will be made with the 3D printer.
- The carter/lower part you have the carter itself, crankshaft and piston arm which connects the crankshaft with the piston. I'm planning to make these parts with the laser cutter.
One of the criteria for the course is to use a third electric machine of choice. So I will be using a drill to drill out holes of moving parts. The 3D printer can make holes but are not that exact which are needed to make it all moving smooth. And probably a hot glue gun will also be used to glue LED's in place.
In the sketch the LED's are not placed yet but they will be place in de inlet- and exhaust port and in the spark plug. They will be lit in order of the inlet stroke, exhaust stroke and spark. This will help show the operation of the engine.
A few remarks are put in the drawing in Dutch so I will translate them for you:
Engine block in three parts:
- Carter/lower part
- LED in inlet port
- LED in exhaust port
- (servo)motor in crankshaft
*LED's simulate the inlet- and exhaust stroke and the spark of the spark plug
*Proportions are incorrect "
With this concept it's also important to know what to make and what definitely isn't possible within the time span of this course. To set the boundaries a MoSCoW list is made:
- Must have moving piston in a cilinder, moving crankshaft powered by a servo or motor
- Should have LED(s) for decorative lighting
- Could have LED's for simulation of ignition
- Won't have detailed parts like valve tappets and -guides
Parts list and production methods:
- Engine block (3D printer, drill)
- Crankshaft (lasercutter)
- Pistonarm (lasercutter)
- Piston (3D printer, drill)
A global planning is made to be sure everything is made within the time span of the course. Because it's my first time I'm working with the 3D printer and lasercutter, the planning is a raw estimation.
- Week 1
- First try on the 3D printer. A simple dice is made
- Week 2
- Drawing of the complete product in 2D and 3D
- Getting used to 2D sketching with Inkscape
- Making of the engine block parts with cylinder but without cylinder head. Made with the 3D printer and drill
- Making of the piston with the 3D printer and drill
- Making of the piston arm with the lasercutter and drill
- Making of the crankshaft with the 3D printer for the axle and the lasercutter for the asymmetrical part
- Assembly of the existing parts, modify to fit for a smooth running
- Making of the parts to couple the motor to the assembly. Propably made with the 3D printer
- Drilling holes for the LEDs and putting the LEDs in
- Assembly of the motor to the rest
- Making of the cylinder head with the 3D printer and drill
- If time is available: making of the camshafts with the 3D printer
- Making of the valves
- Drilling holes for the LEDs and putting the LEDs in
- Assembly of the complete product
- Product evaluation
- If needed: making of small adaptations
Step 2: Create 2D and 3D Drawings for Fitting
As an Automotive student I have some experience with modelling with Autodesk Inventor©. This is a common used program to make 2D as well as 3D drawings. This comes in handy because the 2D and 3D drawings are necessary to make 2D lasercut and 3D printed objects.
Within Autodesk Inventor© it's possible to export 2D drawings from 3D drawings. The other way around isn't easy, that's why it's easier to make the 3D drawings first. All of the drawings are included, so if you're lazy and don't want to draw them yourself, you can download them and use them right away.
I used the following order for making the 3D drawings. This doesn't mean you need to follow this order yourself but I found this the easiest way to make sure everything will fit and look a little bit on scale:
- At first I made the piston. Like everything it isn't at scale but a simplified version of the real deal. The piston is 50 mm in diameter and 35 mm high. The top is flat which makes it easier to 3D print. Or else the printer needs to use support material which I wanted to prevent. A 10 mm hole from on side to another is made to put in a pin which connect the piston with a piston arm. You could make this hole any size you want, I have chosen 10 mm as an aluminium tube can be bought at your local hardware/DIY store.
- Then the cylinder is drawn in 3D. To make sure the piston can move freely within the cylinder, the inside diameter of the cylinder is set to 50.2 mm. This is 0.2 mm wider than the piston itself which should be enough. You can make the outside diameter any size you want but I do recommend to make it big enough to give some strength. I made the wall 10 mm thick. On the bottom side I made the outer diameter a bit smaller so this will be fit into the housing. The overall height of the cylinder is 80 mm, which is determined by the stroke length of the piston. The stroke length is 40 mm which means the cylinder has to be at least 75 mm to make sure the piston can move entirely within the cylinder.
- Next is the crankshaft. This is the asymmetric part which determines the stroke length. The bottom part is a half circle which you can make it as big as you want. I made it 60 mm in diameter, just because of its looks compared to the rest. On the opposite side of its center point a 5 mm hole is made for the bolt which connects the crankshaft with the piston arm. Again, you can make this any size you want. I used 5 mm because I had the bolt and ball bearing already laying around. The distance between this hole and the center point is 20 mm, which gives a total stroke length of 40 mm. The center point is going to be pressure fitted on the motor axle which is quite precise. Some experimenting is needed to make it work as it's dependent on the type of motor and laser cutter you use.
- Then the piston arm is made in a 3D drawing. To determine its size I made an assembly in Inventor© in which I placed the already made components in the right places. The overall size of the arm is 85 mm long and 32 mm wide. The distance between the holes for the ball bearing and the pen in the piston is 65 mm. These are good dimensions to avoid any parts hitting each other like the crankshaft and the piston. On the top a hole of 10 mm is made where on the bottom a 15.9 mm hole is made. I made this 15.9 mm because I had a 16 mm ballbearing laying around which I could use. It's not required to use a ballbearing but I thought it would be a nice little extra.
- The next parts are the pieces for the housing. First I wanted to make a nearly enclosed housing with the 3D printer which is a scaled version of a real engine. But I made it much more simple and more open to show the moving parts. On the upper part of the housing I drew a flat 5 mm thick piece with a hole in it for the cylinder. On the sides I made a puzzle like connection for the side parts of the housing. It's going to be made of 5 mm frosted white acrylic.
- The side parts are also 5 mm thick and are very open to show as much as possible of the moving parts within. On the top sides of the side walls are also puzzle like connections made which are pressure fitted in the top part. The overall height of the walls are 70 mm which is big enough to make sure the moving parts won't touch anything. In the walls are a few slots which are made to connect the motormount to these walls. The location of these slots depends on the type of motor you use to drive the crankshaft. Most important is the length of the shaft of the motor. The tip must not go any further than the crankshaft or else this shaft will block the piston arm from moving.
- The next part to draw is the motor mount. This is a fairly simple piece which is 90 mm wide and 45 mm high. On both sides are puzzle like features which are corresponding to the slots in de side parts of the housing. The holes depends on the type of motor you're going to use. In my motormount are four holes made, three for the mounting screws and one for the motorshaft.
- The last parts to draw are the cooling fins. My intention was to use (semi) transparent acrylic so when a LED or other light source is put behind it, it would lit up nicely around the cylinder. The outside diameter can be made by choice. The inside diameter needs to be the same as the outside of the cylinder when these fins are going to be glued. I chose to make them just a bit smaller so they fit nice and snug around the cylinder so no glue is needed. The dimensions I chose for the inside diameter is 69.8 mm and the outside diameters are 100, 110 and 120 (3x)mm.
(- Just for illustrative purposes I also made a 3D drawing of the motor. Just to show how it all should look like and for digital fitting of the complete object. This 3D drawing is also included)
- Electro motor.ipt
Step 3: Printing and Cutting a Few Test Parts
Then comes the most exciting part, creating the parts with the 2D lasercutter and 3D printer.
First I made a test cylinder and piston to check if it would move smoothly in each other. The downside of 3D printing are the corrugations. Surprisingly enough this didn't turned out to be a problem if the fitting isn't too tight. Although it greatly depends on the type of printer so recommend to do some test parts yourself. For the test I made a 1:2 scale simplified cylinder and piston.
For the puzzle like slots in the lower housing parts and the pressure fitted crankshaft, it's recommended to also make some test parts because of the accuracy of the laser cutter. I made these parts immediately in the hope they will fit snugly but they didn't. So I made them a second time, with success. The final drawings are included.
Step 4: Printing and Cutting the Final Parts
Now it's time to make the final parts. You can make these parts any color you want. Just keep in mind what you want to do with the final product in the future like putting in some lights etc.
After you printed and cut them, you probably have to do some sanding to make everything fit nicely. Especially the piston arm where the ball bearing is pressure fitted. It's imported that is won't come out so be sure you check it often before you sand it too much.
It also can occur that the piston won't move smoothly within the cylinder because of the cooling fins. As mentioned earlier these are a tiny bit smaller than the cylinder so they don't have to be glued in place. But by doing this, the cylinder will be compressed a little bit by them. I used sanding paper to sand the piston just that little bit so it fits nicely.
Step 5: Assembly
Now it's time to put it all together.
There isn't really a best way for doing this but this is the order of assembly I used:
- First I mounted the motor on the motor mount with three screws ( amount and type depends on your type of motor). Carefully tighten them but not too tight. Acrylic is fairly brittle so the risk of cracking it is present when you over tighten them.
- After this I pressed the crankshaft onto the motor. How much effort this takes depends on the precision you made into the laser cut hole.
- In the bottom of the piston arm a ball bearing is pressure fitted. Again, be sure you won't need too much effort to fit it in or else the acrylic will crack. If it doesn't fit, just roll a bit of sandpaper into a little cylinder. Then turn this cylinder into the hole against the direction in which you rolled the sandpaper. The sandpaper will push itself against the hole which makes it a bit easier to make the hole bigger. I used grain 120 which works quite nicely.
- Now you can put the piston arm on the crankshaft by using the M5x20mm bolt, rings and nut. Put a ring between the piston arm and crankshaft to make sure these parts won't contact each other while turning. A ring between the crankshaft and nut isn't really necessary but more advisable.
- After this assemble the lower housing parts; the sidewalls and the upper part of the housing. My sidewalls and motor mount fitted nicely, but this was more luck than advanced calculation. The upper part for instance didn't fit, the puzzle like connections were too different so it won't stay in place when assembled. For this, I made the tolerances a bit too small. I preferred to sand a bit to make it fit than make the part again with the laser cutter of 3D printer.
- The cylinder is placed next. Because the piston will be moving up and down the cylinder, I chose to glue the cylinder to the top of the housing. Not really necessary when the piston can move freely within the cylinder.
- Now it's time to assemble the piston arm with the piston. To do this, you need the aluminum tube which acts as a axle between the two parts. Make sure that this tube fits snug in the piston but turns smoothly within the piston arm. If this is not the case, use the same method of sanding in the step above with the sanding method for the bearing.
- Then it's time to assemble the cooling fins. This is just simply fitting and sliding the fins to the right height. I made the fins a tin bit smaller than the cylinder so I don't have to glue them. A downside is, the cylinder will be become a bit smaller due the pressure of the fins. In my case, I needed to make the piston equally smaller. For this I just used sandpaper with grain 120 until it moved nicely in the cylinder.
- After this assembly is complete, it's necessary to provide it with a power source. I used a DC motor controller from eBay which I already had laying around for a time lapse slider. You can use a direct power source as long you make sure it's DC current and that the voltage isn't higher than the motor can handle.
Now it's complete and ready to be used as a decoration.
Step 6: Extra's
Unfortunately I didn't had the time to make the Should and Could Have's of the MoSCoW list. But it's possible to put in some LED's behind the cooling fins. In order to do this you have to be a little bit creative though. In the 3D drawing of the cylinder I made some holes which run from the bottom to the top. These are channels to put the wires in for the LED's which are put in the holes which you need to drill at the desired height. For this you have to use very thin wires because these channels are relatively small. If you want to do this, be sure you don't drill too far or else there will be visible holes on the inner surface of the cylinder.
For the lighting of the fins, I used five 3mm white LED's which have a emitting field of 90 degrees. This spreads nicely within the clear acrylic. Just be sure you put the LED's against the fins and even glue them to the fins with clear glue. This will prevent any light from leak or bounce of the side of the acrylic where the LED's are placed.
Unfortunately I didn't had the time to specify this circuit completely but I will post this a little time later, I promise.
Until then, enjoy this tutorial and of course: build your own!