Currently there are many challenges around the world about dropping an egg safely from a desired height. Not only for fun, but as scientific experiments many university students are trying to achieve this task for their physics lessons. We can find many designs on the internet, but most of them are just made for fun. Here I will show you how to build an egg dropping machine with a good scientific approach. I have tested this up to 25m without cracking the egg. Further this contains a mechanism which allows the egg to come out and touch the ground after landing.
This device contains 2 main parts.
2) Shock absorbing capsule
Let’s focus on the parachute first.
Step 1: Making the Parachute
Parachute is a good method of slowing down free falling objects in the air. You all might have built small parachutes from polythene sheets and garbage bags as a hobby. But there are several theories and calculations related to parachutes. When designing a parachute we have to consider about the terminal velocity and drifting. Drifting is coming down with an angle without coming down straight. The dimensions I mention here are calculated for a weight between 500g-800g for a minimum drifting. The maximum drift I got for 25m height is 1.8m.
We need following materials.
1) 80cmX80cm silk material or polythene(Here I have used a silk material)
2) Marker and a Ruler
3) A pair of scissors
4) A Needle and threads
5) Super Glue
Mark a circle with 80cm diameter on the silk material and cut it out. Then mark a small circle in the center with a diameter of 2cm and 4 lines symmetrically according to the diagram. Now stitch the lines with your thread. Leave 40cm length of thread (1st Image), free from each end. Glue the stitch lines thoroughly (2nd Image). Cut the hole in the center and rectangular shapes shown in the diagram out and make sure the stitch lines are still holding the silk material well.
Next we have to tie all the parachute lines with equal length. Hold all 8 threads together leaving 10cm from free from the end. Wrap them with another string and glue them to make sure that they do not slip (3rd Image)
Semi sphere is a parachute shape which creates the highest air drag. Therefore when deploying this, an instant tension force will exert on the weight which can make a horizontal movement. This will cause a considerable drift when landing. To avoid this we make a hole in top of the parachute which allows to escape the air inside the parachute and distribute the force gradually. Side holes are called steering holes. This allows to escape the air in horizontal directions and make sure that parachute doesn’t drift and lands vertically.
Step 2: Shock Absorbing Parts
Now we make the main shock absorbing parts. Collect following items.
1) Piece of cloth (approx. 12cmX24cm)
3) Sponge cube around 6cm each side
To make the sand bag cut 2 circles with a diameter of 12cm. Stitch them together from boundary line leaving a small hole to fill sand. Fill your bag with sand until it weighs around 500 grams. Thickness should be around 3cm.(1st Image)
Take the sponge cube and mark a circle with a size of an egg in the center. This is where we keep the egg while dropping. Now carve a semi spherical shape within that circle to put the egg.(2nd and 3rd Images)
Sand bag is a very good method to absorb the shock. Even to make bunkers in military they use sand bags because it provides a massive resistance to bullets. The main advantage is, it doesn’t bump back like springs and sponges after absorbing the shock. Therefore we use the sand bag as our primary shock absorbing method.
Egg holding sponge cube is the protective case for the egg. We cannot place the egg on its any side. The bottom part of the egg have more strength when we observe the force distribution over the shell. So we place the egg as shown in the last figure.
Step 3: Making the Body
Let’s make the device body. Find the following things.
1) 1cm thick sponge sheet ( one square meter would be enough)
2) A hot glue gun.
3) 30cm long plastic tube with 10cm diameter
4) Styrofoam ball with a diameter of about 12cm
5) Piece of an advertising board or some other cartoon board.
6) Cutting knife or a Blade
Take the Styrofoam ball(1st Image) and the plastic tube. Keep the plastic tube on the Styrofoam ball and make a cut on the ball about 5mm deep around the tube’s boundary. Then press the tube to the ball until it goes about 2cm deep.(2nd Image) Apply some hot glue to the hole and hold the tube until it fits. Also apply some glue around the tube.
Cut a 12cm diameter circle from the sponge layer and glue it to the bottom of the Styrofoam ball.
Cut 4 pieces from cartoon/advertising board having a 10cmX5cm size. Glue 2 pieces according to the diagram. Continue this step to the opposite side. These pieces are called fins.(3rd,4th, 5th and 6th Images)
Fill the plastic tube up to 10cm from small sponge pieces ripped from the sheet and press them to pack tightly. Cover the rest of the tube by sticking the sponge sheet inside.(Last Image)
Spheres can distribute applied forces equally within it. Here, Styrofoam ball will exert the shock forces on tube, equally. Fins make sure that the tube will always fall only on 2 sides.Watch the attached video. Sponge pieces are good method than using a single sponge piece to reduce bumping back the top weight.
Step 4: Finalizing the Design
Now all we have to do is put all things together and finalize.
Take the sand bag and plastic tube with ball. Glue the sand bag to the bottom sponge layer of the Styrofoam ball using hot glue(1st Image). Place the egg holding sponge cube inside the tube and press it down to fit it tightly. (2nd Image) Basically your egg lander is ready now.
But wait! If you place an egg and drop it with a height of about 2m you can notice the egg will land safely and bump out of the tube and crack. Now we have to stop this. Collect following items.
1) Piece of cardboard
2) 2 Nuts and Bolts
3) A thin metal wire
Cut a 10cmX20cm size cardboard piece and glue a foam layer on it. Cut it according to the 3rd Image, so that it can placed as in the 4th Image. Then make two holes at the top of the plastic tube, at exact positions of fins leaving 2cm margin from the top. Now fold and place the cardboard piece and put 2 nuts and bolts through the holes and tight the cardboard piece to plastic tube(5th and 6th Images). Make sure egg slightly fits to 2 open areas(7th Image). Now tie the metal wire to the 2 nuts which we use to tie the parachute line as in 6th Image.
When the device hits the floor sandbag absorb the shock and hold the device from bumping. The force from sand bag will be applied on the Styrofoam ball through the sponge layer and Styrofoam ball distributes it equally to plastic tube walls. With this deceleration, sponge pieces will press down and force will be exerted on the bottom side of the egg. Then sponge layers will release the stored energy due to compression which will cause the egg, bump out. But top cardboard layer will avoid the egg, bumping out from the device. After that the device will fall only on two sides which do not have fins. If it falls on fins as it’s unstable it will roll to other side. Simply the device will not fall down on fin sides. After falling down you can notice one of the two openings of the top cardboard arc, is placed towards the floor. Then the egg will roll down, and touch the ground through that opening.
Step 5: Testing
Now we test our device. Tie the parachute line to the metal wire. Then place the egg vertically on the egg holding sponge. Choose a height between 10m-25m. Now hold the parachute while letting the device to hang on parachute lines.
Get ready…..Release the parachute….. Check your egg after landing.
This is a very good device for competitions as well as Easter parties. Enjoy your egg landing machine. No more cracked eggs.
The attached video shows a free drop from 2m height. It's terminal velocity is nearly equal to dropping this with the parachute from 25m height. Hope to upload a full video soon.