Introduction: Pas-car (Pascal Car, You Know As in Pressure?)
I love Pelton Turbines, I think they are a wonderful piece of engineering. I've been thinking of a way to make a fun application with one of these turbines and several ideas have emerged, one that appeals to me a lot is building a toy car that uses it as a means of propulsion. Although the Pelton Turbine was designed and built to take advantage of the linear movement of fluids such as water, I would like to experiment with compressed air also and see what results can be obtained.
In the following INSTRUCTABLE I propose a toy car powered by compressed air that hits a Pelton turbine. The movement of the air flow against the blades of the turbine causes a rotary movement that is transmitted to a pair of wheels by gears. The compressed air tank is placed in such a way that also the minimal force derived from the release of pressure causes forward motion to the body of the car. The fundamental parts of this car have been designed in 3D software design tools and a 3D printer has been used to build them. You will also need other materials that are stated below.
- 3D parts printed with thermoplastics (ABS and PETG recommended)
- 2L soda bottle
- 2 x Bicycle chamber air valves
- 4mm inner diameter silicone hose
- 8 x 624Z bearings
- Instant glue and silicone
- Tools and utensils
- Manual or electric pneumatic pump
- Pressure gauge (optional)
- Pressure clamp
Step 1: Build All the Parts From the Design
What's truly interesting about this project is that the bearings are the only parts that are not made out of plastic, the entire chassis can be made out of plastic either in a 3D printer or using other manufacturing techniques. Silicone or glue is only used in cases where the printing part might have gone wrong or had a slight imperfection. The entire design was made to use only fixing pins and nuts and bolts made also out of plastic.
The entire build guide for the parts is as follows:
- The entire setup uses 8 bearings, 2 of them to the main gears along side the turbine and 6 to the chassis. The ones that are fixed to the chassis need two halves of a fixer, you will need to print 6x bearing_fixer_1.stl and 6x bearing_fixer_2.stl.
- The entire toy car uses 33 bolts and nuts, so: 33x bolt.stl and 33x nut.stl.
- You will need 1x chassis.stl.
- The engine or turbine cover was slit in two parts for easier assembly: 1x engine_cover_1.stl and 1x engine_cover_2.stl.
- The toy car uses 3 wheels: 1x main_wheel.stl that needs1x main_wheel_pin.stl and2x rear_wheel.stl.
- Attached to the turbine are 2 motion trains on each side, one for backward motion and one for forward. The two backward motion trains use 6 fixing pins to hold them in place. You will need: 2x inverse_train.stl, 6x train_fix_pin.stl and 2x train_forward.stl.
When finished printing (and cleaning each part), you should end up with pieces like the ones in the pictures. You might also want to test out the turbine and see if it is efficient and there's no fluid leaving the center blades in an orthogonal angle.
Step 2: Engine Assembly
The engine of the toy car is made with a Pelton turbine attached to gear mechanisms that transmits motion to wheels in the rear part of the car. On each side of the turbine there will be a backward motion train that will be held in place with 6 fixing pins (the same 6 fixing pins hold the two trains together, the guide in the diagram show two sets only to state the fact that the insertion can occur from either side of the turbine).
As a design measure to better balance the turbine in place, only 3 pins can be inserted from each side as each train only has 3 accessible pin holes as you can see highlighted in orange in the diagram.
After inserting the first 3 pins, you'll have to turn the turbine over, rotate the other train so that the 3 accessible pins there will be aligned to the 3 pin holes on the other side.
When this assembly is complete the only thing left to do is attach a bearing on the out most tip of each train and your setup should resemble the one in the picture. If you wish to strengthen the setup with some glue or silicone on each pin hole you're welcome to, but it is not necessary.
Step 3: Engine Cover
The engine or turbine cover is built joining two parts that hold the turbine in place with a nesting point for each bearing in the tip of each train. You'll notice each part isn't symmetrical but the fluid intake for the turbine is, and it's aligned in the center. The reason for this is that while some fluid may leave the turbine cover through the hinges, we remove the possibility of fluid leaving the intake altogether.
When joining the two halves take special care to ensure the bearings rest in the points highlighted in orange in the diagram so that there is less friction when the turbine turns. Also, the blades of the turbine with the inner split must face the intake nozzle, from there the fluid will hit it directly. When everything is properly aligned, hold the two halves in place with 5 bolts and nuts through the sections highlighted in green.
When everything is done, it should resemble something like the part in the picture.
Step 4: Forward Gear and Rear Assembly
To fix the engine block (turbine with trains + cover) to the chassis you will need 4 bolts and nuts through the parts highlighted in red.
You'll need to assemble two forward trains that go on each side of the engine block. Each train is made out of 3 parts: 1 forward gear and 2 bearing fixers. Each bearing fixer must be assembled joining two bearing fixer halves with a bearing in the middle like the guide depicted in the pictures. The setup highlighted in orange shows how the forward gear and the two bearing fixers are assembled. When you've finished building the other side (1 gear and 2 fixers also) fix both parts in place with 4 bolts and nuts for each fixer against the chassis from below as depicted in light green and be sure to align both the gears in the forward and backward train by sliding the center axis of the forward train until you've found the best contact position as depicted in blue.
When you're good to go, attach a rear wheel on each side of the forward gear axis, fix it in place with instant glue, and you're all set.
After finishing your parts should resemble the one in the pictures.
Step 5: Main Wheel Assembly
The assembly of the main wheel is fairly easy, you need 2 bearing fixers (which you already know how to build), one main wheel and one main wheel pin. Slide the main wheel pin through the main wheel and assemble two bearing fixers, one on each side of the main wheel. Join the bearing fixers to the chassis in the sections highlighted in green.
Your setup so far should be looking something like the picture. I used a different style of chassis, mine's two lengthy pieces of plywood since I ran out of plastic.
Step 6: Build the Air Cannister
The pressurized air and water is contained inside the 2L soda bottle. To hold them in, we must modify the bottle to ensure that the pressure remains stable using the two bicycle air valves and there are no leaks. First, start off measuring the diameter of the valves so that you know how much to cut in each side of the bottle. Start with the bottom side of the bottle, use pliers to cut open a small opening where one of the valves can slip through in a tight fit. To do this, remove the cap of the bottle, insert the valve through the main opening and pass it through the newly cut opening, glue from the outside the valve to the bottle.
Now go to the cap, the same procedure applies here, cut an opening, fit the valve through and enjoy here the possibility of gluing from both sides. Finally screw the cap back on. Test the entire setup by pressurizing air inside the bottle with the pump and testing how well you did checking for leaks and pressure. In the picture, the air is pressurized at 20PSI and the bottle looks OK.
When you're sure there are no leaks, deplete the bottle slowly by releasing pressure. When it's empty, remove the interior part of one of the valves with the pliers, and attach one end of the hose and fix it to the outer area of the valve with a pressure clamp like you see in the picture.
Step 7: Put It All Together and Test It Out
Mount the canister in the chassis and hold it in place with zip ties. If you're going to use only pressurized air you can orient the canister in a horizontal way. If you're going to use pressurized air and water in a mix, you need to orient it in such a way that the water will be nearest to the exit valve, so that the pressurized air within pushes it out to the turbine. For this, you can use a light block made out of Styrofoam or cardboard.
In the video you can see how the testing process was carried out.
Step 8: Final Thoughts
The main conclusion is that pressurized water and air provide more propulsion than air by itself. The movement of water through the hose to the turbine as the pressurized air pushes it out creates a differential in pressure that, even after the water manages to exit entirely from the canister, the remaining pressurized air can also provide propulsion. Overall, the toy car manages to achieve greater speed and distance with the mix.
The design proposed is robust, the toy car held together structurally through every test, validating the preliminary work. It is a fun and exciting project to develop. :)
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Make it Move