Re: Propulsion that does not involve driving wheels
 

I'm not questioning whether the GDC is going to come eventually outlaw vacuum systems if Bill thinks they're going to outlaw it... But that sounds like a pretty specious justification right there. Especially as you're only penalized for damaging the arena if you damage it. If you can prove you won't damage it, then you should still be allowed to operate under that reasoning.

Re: Propulsion that does not involve driving wheels
 

Bill's Blog is actually quite encouraging for vacuum proponents. If you can design a system which doesn't damage the field then Bill's blog implies that it would be legal.
As for the working on the moon argument--on the moon you could stick on some hydrazine thrusters, but you obviously can not do that in FISRT. There are differences between the playing environment and the moon.

Re: Propulsion that does not involve driving wheels
 

We'll be competing in Trenton, NJ, which (last I heard) has an atmosphere. And the rules don't say we can't use it.
With a tiny bit more to noise...:D
Oh really? As others have said, if I were to shoot seven moon rocks straight up in the air in 1 second with my 27x37x59 inch robot weighing 120.0 pounds, for a brief time the normal force my robot would exert upon the arena floor would exceed 120.0 pounds. This is perfectly legal, and if you disagree show me the rule.

When they weigh my robot, it is powered off and without a battery - by definition they are not measuring the normal force, they are measuring WEIGHT.

At this point, the argument against using a fan to push you down* is specious at best, and bizarre in my opinion. (*Think of a fan mounted at the 50 inch level - no suction on the floor involved). But, I also admit that I wasn't even thinking of implementing this at any time.

OK, so my original post was about using fans to propel a vehicle horizontally like a swamp boat. Our current progress is measuring the forces this can generate. We will absolutely also be using a conventional drivetrain - as someone said in the Hovercraft thread, why give up what propulsion you can get easily? My thought is to double the propulsive force offered by the wheels, and I am looking for a 12" fan blade with which to experiment.

Don

Re: Propulsion that does not involve driving wheels
 

Running with Don's return to the original post:

238 ran a test that involved attached a 16" diameter RC airplane propeller to the output shaft of a Fisher Price motor. We rigged it to a digital bathroom scale with 0.5 lb resolution, put our safety glasses on, and turned it on. Registered weight difference: 0 lbs.

Now, there are a variety of things that we could have done wrong. It may be that the battery wasn't fully charged, our scale wasn't one of quality, or that our motor had seen better days. We definitely weren't operating the propeller at its ideal rotational speed or airspeed. These are issues that we would love to pursue, but we're going to focus on wheels first. Let us know what you find out. Good luck!

Re: Propulsion that does not involve driving wheels
 

I was a proponet of the fan boat idea untill I took an old twin radiator fan out of a dodge and tried to blow a cell; it didn't move. The cells have too many holes that let air thru. So blowing balls away looks a little busted. Although last year they said the same thing about launchers and shooters and see how that turned out:p We'll see, someone will find a way lol;).


*after thought* : if could have been because I was using a dodge fan. everyone knows those things are weak:cool:

Re: Propulsion that does not involve driving wheels
 

As long as it wasn't powered by a Dodge starter motor ;)

Re: Propulsion that does not involve driving wheels
 

The problem with your 16" prop especially if it was directly on the output of the FP was you had way too much prop diameter there. If you were to put the same on the CIM you would see a difference, and if you gear the CIM up by oh 1:2 then im guessing you may see even more. However, a reduction in diameter doesn't equal a increase or reduction in pitch of the prop in all cases either.
for instance try turning your 16" prop at around 4000rpm or more and see what it does!

this video
http://www.youtube.com/watch?v=ccGVZRG8DdM
shows 26" diameter blades, variable pitch up to 10 degrees or so, and a motor consuming 350 watts and that heli weighs about 1.87lb and normal rotor speed for those is usually near 3000 rpm
Here a slightly lighter heli lifts 2000grams, thats 4.4lbs plus its own 1.5lb weight. using an 11.1v battery and a 35A speed controller so he had 388W of power, granted using a brush less motor. This would be the coolest thing... both to see and feel.. thats some major air movement!!
http://www.rcgroups.com/forums/showp...ostcount=12275

Re: Propulsion that does not involve driving wheels
 

Incidentally, the GDC has allowed using propellers on the robot in Q&A.

Still no word on making a nice big downforce, but one thing at a time.

Re: Propulsion that does not involve driving wheels
 

im still leaning towards our chepo-swerve drive.....

another problem with fans is they would take up lots of space for ball collecters ans such....

Re: Propulsion that does not involve driving wheels
 

A few members of our team calculated how much thrust we could get with a leaf blower (reconfigured to run on kit motors), and with 2 1/2 hp (2 FP's and 2 CIMs) it would barely provide more thrust than possible with the wheels. This is with a 120 CFM, 150 MPH (iirc, but I know it was that ballpark) blower. For such a small advantage, this would be a very dangerous system (fast moving air + any debris/dirt/unprotected eyes = bad situation).

Re: Propulsion that does not involve driving wheels
 

IMHO I don't think that trying to create downforce will bear much fruit. Use that force for propulsion instead.
Indeed. So if we take this one step further: Mount the leaf blower AND use driven wheels... then you'd be something like twice as fast maneuverable as anyone else... Think that'll bring any advantages?

Re: Propulsion that does not involve driving wheels
 

I don't think leaf blowers are the appropriate model for an air-based propulsion system for a robot. They're very much about accelerating a fairly small amount of air to rather high velocities in as small a space as possible. They generally do this by generating a (relatively) high pressure differential using an impeller. This isn't nearly as efficient at producing thrust as something like a propeller or fan. These are designed for moving much larger masses of air, but at somewhat lower speed and vastly smaller pressure differentials. So, I think you're much more likely to generate a useful amount of thrust with fans or propellers, as opposed to leaf blowers.

Re: Propulsion that does not involve driving wheels
 

The Q&A question referred to a model aircraft propeller in a "ducted fan" configuration. If you can do it...

Re: Propulsion that does not involve driving wheels
 

Actually none of this is neccesary..the floor is drivable..you just need to think how to use it too ur advantage

Re: Propulsion that does not involve driving wheels
 

I agre with this. I believe getting every little bit of traction from the wheels, make them all powered, steer, and just practice driving a lot.