Vid:
Tell me if you want some specs. or whatnot.
try a condensor fan from an airconditioner, works great;)
Have you tested to see if it (or 4 of them) can generate enough force to move your robot?
Have you measured the thrust this produces?
If you noticed, those fans remain stationary. Their high pitch allows them to push a lot of air, yet have minimal thrust because of all the stalling. I’m pretty sure it wouldn’t be a good idea. We’re currently running 12.25 - 3.75 plane props which at meant for maximum thurst.
Can some other team argue that this interferes with their robot’s movement? Just curious.
If it has enough thrust to have any effect on your robot, then why not on the robot in front of you?
Anyone?
Not yet, we haven’t had time to make a rig to measure it, or obtain a newton meter for that matter =/
If you say that, then perhaps bumping into other robots should be illegal?
Anyone?
=P
Umm that wasn’t a hit at your design
It was a serious question.
You probably could argue that it interferes with your robots movement, but IIRC there’s no rule that says interfering with another robots movement is illegal. So, arguing that it interferes with you would be irrelevant.
Yeah i know, but i don’t see why it would be any different from physical contact such as bumping and throwing balls at each other.
I mean, it is part of our plan to abuse the fact that we might be able to blow balls away from our trailer, but really, nothings stopping any other team from making a fan, right? =)
Wrong tone? Do i sound bitter or sarcastic or something? Sorry XD
I think he’s mainly referring to the word “abuse.” So in other words yeah… I think it’s you’re tone. In other news your “sorry” seemed pretty much sarcastic with your XD at the end of it lol.
Just drop it. Its cool.
woot, 1403 post, Cougar Robotics
To return to the original point of the message. Thank you for the demonstration–while you don’t have a newton meter avaliabe it is very simple to build something which will have a similar effect. Take a box and suspend it making a pendulum (longer suspension will mean greater accuracy), mount your fan set up on it and let her rip. By measuring the angle off normal created when your fan is turned on and using a simple bathroom scale to measure the mass of the box and your fan set up you will have more than enough accuracy. Here’s the math:
Fractional force of gravity pointing in the horizontal direction: Fgx
Force due to gravity: Fg
Angle created by string from normal: theta
Fgx=Fgsin(theta) By inspection
Fprop=Fgsin(theta)
Note that this lets you give a force in Lbs which are much nicer than newtons.
For teams looking into propeller propulsion here are some helpful hints:
Static thrust depends ONLY on prop diameter and RPM, Pitch only impacts power use and top speed. So you will want the largest diameter, lowest pitch prop you can mount, and spin it as fast you can.
Look at the power curve for the motor you have chosen, and select a prop that will run at the peak power point.
To find where a prop might run, here is a link to download a freeware program of great benefit. The page is in German, but the program is in English. The download link is at the top left of the page. The program is called THRUSTHP.
http://www.hoppenbrouwer-home.nl/ikarus/software/thrusthpv20d.htm
Here is the calculator we used to calculate the maximum thrust and size of engine required:
http://personal.osi.hu/fuzesisz/strc_eng/index.htm
As others have said the pitch of the props have no effect on static thrust, only the maximum speed at which the craft will be traveling it, and the pitch have enormous effect on the engine. To other teams attempting this method of propulsion, use the smallest pitch you can find (12.25x3.75 was the smallest we found). It will provide the same thrust and require less power.
Due to a loose belt during our first test run, we couldn’t run the prop up to full speed 
Spinning that blade at 10k rpm according to our calculator (from above) we will get about 6lb of thrust (12lbs total with 2 of them). Is 12 lbs of thrust enough to move the robots?
Our other possibilities for props are using a 28x4 (still havn’t found a low pitch prop this big) spinning at much lower speeds to get more thrust. and one more question if anyone knows this, besides requiring more power, is there a reason to use a 2 prop vs a 4prop blade? Using a 4 blade 28x4 prop spinning at 3500 r, according to this calculator (above) would provide nearly 35lbs of thrust
I seem to recall some theoretical math stating the CIMs driving a wheel on the floor could only generate 9 lbs of thrust, so it might be feasible.
A two bladed prop is more efficient than a 4 bladed one. Don’t ask me how I know though because it was demonstrated to my R/C flying club one year. If you could make a 1 bladed prop that would be the most efficient.
Please, please, please do not exceed the max. rpm rating for the prop. I’ve seen blades break and imbed themselves into wooden benches 10 feet away.
These props are not toys and should be treated as you would a circular saw.
I know you will use proper guarding around the prop. If a prop gets knicked THROW IT AWAY!!!
Other than that it looks like it would do the job of moving your bot around. I think the only problem you will see is a slow take off (no pun intended 
)from a dead stop.
BTW I have been flying model airplanes for 30+ years.
Btw, just to clear some stuff up, we plan on having two of these prop and motor systems, hooked up together with like a car driving system. Seeing as how Max power of the CIM motors occur at 2671 RPM, the RPMs on the prop would be 3.5 times that. I’d guess that been the minimum, so the RPMs would range from the max power RPMs(2671) to the free load RPMs (5342), resulting in the prop RPMs ranging from 8348.5 to 18697. But due to imperfections such as friction and air resistance, it’s pretty much guaranteed that it won’t be spinning nearly as fast as the free load speed.
Oh and final, there will be a steel wire safety housing around each prop. =D