Intro: Octanis 1: How to Make Parachutes
Octanis 1 will fly to Antarctica and land a satellite controlled rover. To do this, it needs parachutes that will reduce its landing velocity! Here's a guide on how to make Octanis' parachutes. Find out more about the rover mission: http://octanis.org/
Step 1: Calculate the Area of Your Parachute
For our rover that is 2Kg and we want it to land with a velocity of 4.5 m/s the final area of the parachute will be 3.42 m2 and the diameter 2.08 m.
You can calculate this depending on how heavy is your payload and how slow you want it to land, the recommended landing velocity is between 3.5 to 4.5 m/s
Here you'll find a detailed way of how to calculate it yourself:
Like our parachute will be use in an altitude smaller than 1600m, I use the dragging equation:
Where W stands for the weight, ρ is the air density, c the dragging coefficient, Vterm the terminal velocity and A the area of the parachute.
The Vterm will be 4.5 m/s, c is 0.47, ρ=1.27 Kgm3
So the Area of our parachute must be calculate with the formula and for a round parachute, we may want to calculate the diameter d=sqrt(4.A/pi)
Step 2: Cut the Round Shape
You can use any material that's light enough, preferable nylon and cut the circle with the exact diameter you calculate before.
The cheapest option are the IKEA umbrellas, if you're using this ones too you just need to cut the borders or in our case untie them from the metallic part, just be careful unleashing the endings and the center.
Step 3: Cut a Hole in the Midle of the Circle
This hole will help us to gain stability really fast, its diameter should between 15% and 20% of the total diameter of your parachute, in our case the total diameter is 2.08m so its 15% is 0.31m.
Use a compass to draw a circle in the center of your parachute and try to shape as round as possible; don't forget that you'll need to sew the borders of this inner hole so cut a one centimeter less than the calculations.
Step 4: Sew and Harden the Boders
Sew the borders and harden the places where you're going to attach the strings, select at least 12 or 16 symmetrically distributed points around the outer border of the parachute and apply some resine or a second layer of fabric attached with a strong glue. I used nylon thread and some resine in the borders too.
You my want to led it dry under the UV light to get faster results.
Step 5: Cut the Strings and Attach Them to the Parachute
The length of the strings can be as long as you want, just make sure is at least 20% longer that the diameter of your parachute, also you need to attach to the fabric at least 4% of the extremes of your strings.
We made the holes in the hardened points and attached the strings, we made 16 holes and used strings with a length of 2,2 m.