Trying to make a stupid little machine thingy

[Vaughn]

So, i'm trying to make a Fan-type thing out of KNEX, but the motor its got goes way faster than i would like it to. I see my options as
1) Load tons of weight onto it to impede it
2) reduce its powersource.

The power its got is a little box of 2 AA batteries. So my main question is "would reducing it to 1 battery work, and how would i bridge the second batteries gap without setting something on fire"

[Evil Jim]

Add bigger gears between the fan & the motor. This is what an automobile's transmission does.

[Sieg Reyu]

Use half dead batteries.

[Master Gunner]

Add bigger gears between the fan & the motor. This is what an automobile's transmission does.

Exactly. Have the motor attached to a small gear turning a bigger one with 4 times the circumference, and put the fan off the larger gear. Now the fan will be turning at 1/4 the speed of the motor. Adjust gear sizes as needed.

[davefp]

As pointed out above, gears are definitely the way to go. Definitely don't try bridging the gap where the second battery should go. It may not be dangerous per-say, but it's not the right way to go about it.

[AlexanderDitto]

Oh man, I friggin' love these forums.

Your solid grasp of basic mechanics leaves me heartened!

[Rikadyn]

you could also wire in a rheostat

[TomBrend]

Leaving one battery out and bridging the location of the other battery would work fine for bringing the voltage down from 3v to 1.5v, but I would use either a potentiometer (available at radio shack for $3-4) or gears.

[Ottoman]

Gears are better than a potentiometer, though, because you an achieve the same effects on speed without sacrificing any power.

[Vaughn]

Ive got small, medium, and large gears. Should i just go Small-large, or small-medium-large?

[davefp]

small-large. small-medium-large will give you the exact same mechanical advantage as going straight from small to large.

[Ottoman]

Of course, depending on the difference you want, and the relative sizes of the gears, you might want to try small-medium or medium-large, as well.

[empath]

Mechanical Engineering.

I'm with you, Alex" - this sort of thing just warms my heart; 15min after question asked, the most elegant solution provided, and then explained in the intervening time. Other valid solutions provided, but the first wrangles in principles of mechanics, as well as constrains itself to the within the system presented (using K'nex pieces and not bringing in any outside 'jury-rigs')

tl;dr?

[Vaughn]

im devising a plan for small-large, and then have those drive a wheel that spins another wheel that then goes small-large again, and then does the function i want. =D

[Evil Jim]

Please post video or at least photos of your finished project, Vaughn. It will make this discussion even more worthwhile.

[Vaughn]

So hey, after several backtracks and reconfigurings, working with the materials and whatnot, ive figured out i can go SMall-large and then on Large axel, attach a Small beside it, and have that run to another Large. =D

[davefp]

So hey, after several backtracks and reconfigurings, working with the materials and whatnot, ive figured out i can go SMall-large and then on Large axel, attach a Small beside it, and have that run to another Large. =D

Well done! Figuring out mechanics is fun

[Vaughn]

For my desired effect, i think i need a do that exchange 2-3 more times to get it over/around 8 seconds a rotation.

[Metcarfre]

8 seconds a rotation? That's... 7.5 rpm. Quite slow for a fan. Did you attach fresh palm fronds to it or something?

[Dutch guy]

Also, tuning down the voltage is not actually really helping the normal RPM at which the motor runs. Most motors have an optimum speed with whitch they want to run. Halving the voltage doesn't halve this optimum speed, but affects the power tremendously. Hence why gears are better. No loss of power.

[Ed.]

Gears are hard to acquire for Knex I always used to use a rubber belt that i got with one set (was meant for a tracked thing) to transfer power.
Lego is way better for gears.

[Dutch guy]

Lego is way better in each and every way

Fixed that for ya

[Kirkygirl]

@dutch guy:

Lego FTW. Oh dammit! It's the Dutch! AGAIN!

Sorry I had to...

-Kirkygirl

[Ottoman]

Hence why gears are better. No loss of power.

I said that.

[Rikadyn]

remember the old proper erector sets...