General Questions

[Flavorflav]

Ordinary solder does not bond to ni-chrome wire. In my experience, it's better twist the wires together (not an easy thing to do) to make a good mechanical connection or to use alligator clips or similar or some sort of screw-terminal arrangement. For "mid-air" connections you can use a #4 or #6 screw (size is not important) with 2 washers and a nut to clamp the wires together. In any case the constant terminal expansion/contraction tends to cause the connections to loosen over time. It's wise to check their security before each use.

Do you think a wire nut would melt? What do you think of those little jewelry crimp connectors?

DS: thanks for the battery info, and don't worry about looking it up - if they lasted several years, a regular lantern should do well enough for one. Even the heavy duty ones are rated at about 11 Ah, and the alkalines are a little better.

[fleet130]

Do you think a wire nut would melt? What do you think of those little jewelry crimp connectors?

Wire nuts would probably melt unless the current is turned off quickly before the heat has a chance to heat up. The wires are also too small to fit most readily available sizes of wire nuts.

Can't picture the jewelry crimp connectors at the moment, but they would probably work. If they're readily available, you can try them. Another method I forgot to mention is Sta-Kon connectors. They are available from automotive, marine and electronic parts suppliers.

I have seen teams who made up several spare heater wires with a Sta-Kon terminal eye on each end. Their device had screw terminals so they could change the ni-chrome wire easily.

[Dark Sabre]

fleet beat me to posting

Though not called for, the large lantern vs the normal lantern with a 9V for scale:


I don't like Zinc Carbons

I wouldn't use one-time crimp connectors on things like nichrome that might break, just because you have to have more crimp connectors to replace the old ones.

I don't know how your setup works, but mine always depended on keeping the nichrome in tension against whatever I was trying to melt, which would also be in tension...so they were always pressing against each other = reliable transfer. I don't see how wirenuts/crimps/solder could help you keep the wire in tension, so whatever is keeping the nichrome in tension might as well be the electrical contact too :shrug:

fleet's screw+nuts idea would serve both purposes, as would an alligator clip setup (if you compress the neck of the standard RadioShack alligator a little, you can turn it into a cone that you can press-fit into Lego technical pieces or whatever other hole).

[Flavorflav]

Continued thanks to both of you for sharing your experience. I have a couple more questions, if you don't mind:

Fleet: Does the wire have to be very thin? I have some NiChrome that looks like it would work in a small wire nut - it looks like maybe 20 or 22 gauge, if I'm recalling correctly, and was planning on using that. It shouldn't be a problem to find wire nuts for it. DS's point about tensioning might make the wire nuts irrelevant, but I would still like to know if I can expect to run into problems with the thicker wire heating too slowly or something.

DS: I don't know how our setup works either, yet. We are basically still planning and gathering resources - Mission has been out so long we have no reservoir of experience to draw on. Do you mind if I ask what you have against carbon-zinc batteries? They're like a third the price of alkalines and they are rated at about 80% of alkalines' charge capacity, so we were thinking of using them.

[Dark Sabre]

I guess it is particular to the brands that you are looking at, but when I was comparing them, I was seeing Alkalines that were 2x the price of Zinc Carbons with Ah ratios like 20.5:5.9, 8.35:3, 2.85:1.1, which made the Alkalines the favorable purchase. That may have changed...have not looked into it recently.

[Flavorflav]

I guess it is particular to the brands that you are looking at, but when I was comparing them, I was seeing Alkalines that were 2x the price of Zinc Carbons with Ah ratios like 20.5:5.9, 8.35:3, 2.85:1.1, which made the Alkalines the favorable purchase. That may have changed...have not looked into it recently.

Okay, thanks. The economics seem to have changed, and if it's just a question of capacity, enough is as good as a feast.

[cypressfalls Robert]

here are links to pictures of various mission possible machines:
http://www.ee.nmt.edu/~tubesing/mission ... cs2002.htm
http://www.ee.nmt.edu/~tubesing/mission ... cs2004.htm
http://www.ee.nmt.edu/~tubesing/mission ... cs2005.htm



edit/ they are from 2002,2004,2005 repectively

[Dark Sabre]

Nice find! I built all those years
If you are trying to ID transfers, here's what those years (div C) were...

2002:
drop in pingpong ball, move it at least 30cm, and launch it.
hydraulics, pneumatics, chem-->gas, chem-->heat, chem-->EMS (light), chem-->elec, ring a bell
6 energy transfers each of chem, elec, heat, EMS, mech.

In mp_2002_05 I think the thing in the front right is either a hydraulics or pneumatics. I assume the white thing in the back is whichever hydro/pneu the front thing wasn't.

2004:
drop a playing card to start, light a candle sometime, and extinguish it.
pneumatics, hydraulics, home-made electromagnet, permanent magnet, chemical battery, chemical precipitation, increasing heat, decreasing heat, reflection of light, diffraction of light, energy released from a non-mousetrap spring, static electricity, use of an electrical transformer, storing energy in a spring, using a toy that squirts water, playing a harmonica
3 energy transfers each of chem, elec, heat, EMS, mech.

mp_2004_17 looks like it's pneumatics is a vinegar/baking soda mixer that...completes a circuit?
mp_2004_21 has a cool looking pneumatics setup. Looks like nichrome melts a fishing line that is holding the pvc pipe up. There might be a spring on the back? inside the mixture inflates the balloon...and does something we can't see Threaded rod for timing.
mp_2004_23 has syring hydraulics.
mp_2004_30 has a rat trap? Safety rules!
mp_2004_33's electromagnet setup would work this year.
mp_2004_46 has a muffin in it. They have a closed film can with wires coming out of it next to the chemical battery, so that might be dark-room for a photoresistor. Hollowed out Sharpies work too.
mp_2004_50 opted for the brute force method on the photoresistor...left side.

2005:
hold a permanent magnet to the machine, launch a pingpong ball out of the machine and then catch it.
pneumatics, hydraulics, home-made electromagnet, chemical battery, chemical precipitation, increasing heat, decreasing heat, energy released from a non-mousetrap spring, use of an electrical transformer, storing energy in a spring, shaking a baby rattle (can dead end), piezoelectric effect, Bernoulli principle, using fiber optics for all EMS transfers, devices announces school name (state, can dead end).
3 energy transfers each of chem, elec, heat, EMS, mech.

mp_2005_28 has a massive electromagnet (green, right side); you don't need that many wraps.


That's what I saw that seemed noteworthy.
Lots of people look like they were using open system hydro/pneumatics, so most of those are no-gos this year. Their pneumatics also used vinegar, which you can't.

[fleet130]

Update on soldering ni-chrome wire. I found several internet resources that say ni-chrome wire can be soldered using acid-based flux. I haven't tried it as i haven't used acid flux for many years and don't have any at the moment. (I just googled "soldering ni-chrome")
Acid residue on an electronic circuit can cause bad things to happen over time. I don't suppose its as critical in a MP device.

[vofbassist]

My partners and I are having trouble with our mission device. We've got everything planned out and working for the most part, but for the challenge where we have to move the mass for ten seconds is givin' us crap. It either goes too fast and flips the switch at the end, or it goes long enough and lacks sufficient force to flip the switch at the end. Our first tournament is this saturday at our school. If it's not too much trouble, would any of you be willing to tell up what you had work for this challenge? If you can't, that's understandable, but we would appreciate the help.