Archive | May 2012

Final Cost analysis

So I just finished figuring out what we will need to complete our first prototype. Go to the materials page and check out the concept 2. Now for concept 2 we have two choices. We have the 4″ tube and the 3″ tube. The 4″ tube will put us prob around 275 dollars to build (assuming we had to buy everything) and the 3″ is about 250. If we go by the contest rules, the 4″ is right at 250 and the 3″ 225. The 3″ provides us with some breathing room but would not be the most efficient in terms of manufacturing spools. I’m starting to learn towards the 3″ because we should prob start small for our first prototype. I wanna hear your opinion and we can decide what to go with.

Heater Design

The power of the heater will determine how fast the plastic will melt and get to temp. The equation is

Q=mc(Tf-Ti)

Q is the heat given off

m is the mass of the plastic

c is the specific heat constant

Tf is the final temperature

Ti is the starting temperature

The specific heat constant can be found here. It changes based on temp but you use the average of you initial and final temperature.

m=1000g

c= 2.073 J/gK

Tf=200 C

Ti=30 C

Plug that into our equation we need 352410 Joules to melt the plastic.

A watt is a J/s

Say our heater is rated to 175W, it will take 33.56 minutes to heat the pot. This does not take into consideration losses through the walls.

Concept 2, the pot has a capacity of 2-3 kg of plastic. So the 175W heater would take 2-3 times longer to melt.

New concept drawing

I’ve added a different style machine. John and I talked about it last night. It seams a lot simpler than the other one plus its almost all off the shelf parts. About half the cost is the cast iron pipe and cap (60 bucks).  With this current setup, there is enough volume for a few 1kg spools. Check out the drawings and let me know.This could be brought down if we use a smaller diameter pipe but not much. If we went down to a 3″ pipe we would drop 17 bucks.

Lets make it happen

So I wanted to create a way for us to share info and get organized for this. I think we can accomplish this in a reasonable time.

Here is what I think we should base ours on http://www.reprap.org/wiki/Web4deb

If we use this as a base we have a great start.

Rob