Re: Propulsion that does not involve driving wheels
 

To those that think that vertically-oriented fans for downforce are illegal because they alter the maximum tractive force your robot can achieve:

Say you have a robot with a heavy weight on a vertically moving elevator. The weight starts low and can be lifted by a motor. As I lift the weight, my downforce is temporarily increased. If I had a 120 lb robot to start, my weight exceeds 120 lbs when I am in the act of lifting. In fact, any time I change the robot CoG, I alter my apparent weight on the playing surface. If I then lower the mass, my apparent weight decreases. Try it for yourself - stand on a bathroom scale holding a textbook, and watch your weight TEMPORARILY change as you lift it up and down.

Changing the altitude of my robot's center of gravity is something that is allowed. Are we to believe that if your robot will be lifting anything this year, you must account for it in your weight?

-Jared

Re: Propulsion that does not involve driving wheels
 

While I agree that using a fan is VERY questionable due the fact that we are "working on the moon" However if you back and look at the moon rover built and used later on (ask your dad about) T

hey used steering technology from JI CASE (crab steer) and the tire technology I think came from Goodyear. They used a tire that was basically a "wire basket". Take a look, they were way cool!

I found my bucket.... it has a hole in it!

Re: Propulsion that does not involve driving wheels
 

Ah, well. Bill has beaten us.

Re: Propulsion that does not involve driving wheels
 

So sayith first... and so it shall not be done.
But boy it would have been cool.

Re: Propulsion that does not involve driving wheels
 

So my 120 lbs robot is not allowed to pick up any balls? If a robot carries a lot of balls it will have a greater normal force and more traction.

The rule referenced seems to be talking about weight, which by definition is a force due to gravity. Pushing off other objects (such as air with a fan) will result in a greater normal force, not weight.

Back in 2002 there were a lot of robots capable of lifting the primary game piece (a movable goal) specifically to gain normal force for traction. If my memory serves me, this resulted in a lot of torn carpet- but it was legal that year (R29 seems to prohibit similar strategies this year).

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.

Re: Propulsion that does not involve driving wheels
 

Hi Justin,

I'm going to admit that I'm confused by your apparent suggestion that the FP motor spins slower than the CIM. I believe that the CIM's no load is around 5,000 RPM, while the FP's is around 15,000 RPM.

I think that the helicopters have two big advantages - variable pitch and more efficient motors. The variable pitch rotors allow pitch adjustment to match their current airspeed; our prop was optimized for some airspeed greater than 0. I believe that the brushless motors that RC planes and helicopters use are more efficient than our brushed motors. Although the CIM and FP can consume 480 W legally, they only output ~200 W at sustainable currents according to their curves.

Working from this, it makes sense for someone to try and get their hands on a variable pitch prop and try it with a couple of motors, eh?

Re: Propulsion that does not involve driving wheels
 

this idea is amazing. just needs a prototype for testing

Re: Propulsion that does not involve driving wheels
 

What I really meant by saying use a cim was that a FP motor cannot direct drive the prop that you had on the shaft. A prop could be sized for that motor and would be very small relatively 3" or less most likely. The CIM however has more torque directly on the shaft at a slower RPM and would be more likely to be able to direct drive this prop, however it would most likely be too slow also.

If you could measure the speed of that prop on the FP motor Im sure it wasn't going nearly as fast as it needed to be.

If you read back in some of my posts here I do suggest using a model heli head assembly as your variable pitch prop setup. Or even the tail rotor assembly form a rather large model heli, would be a bit simpler to implement.

I do however agree that the motors available to first are less efficient, and never disputed that. I dont expect to see the same amount of power output from these as from a brush less motor. I would also not think of using only a prop as propulsion, only as an aid to propulsion, I think ever little bit will help this year!

EDIT: reading MINISIMON's post agian, wow I didn't realize that those motors were THAT inefficient.

Re: Propulsion that does not involve driving wheels
 

My team (3013) tested what is the lowest wind speed need to move the orbit balls. We used a little wind tunnel that is used for model rocket wind test. We found that it was around the wind speed was around 5.2, but that just slightly moved the orbit ball. but i belive if you can get a small fan that can produce a wind speed of a little more than that then it would work. The only problem that my team sees with the fans is that it might interfere with driving the robot. But we have not build and tested one yet but hopefully we will have our prototype done by tuesday or wednesday of next week. When we get it finished and tested I well post the results.

Re: Propulsion that does not involve driving wheels
 

What about compressed air? Rather then fighting friction with driving wheels. Of course you will need a well built machine for the increased collisions. Use the walls-think billards!

Re: Propulsion that does not involve driving wheels
 

Team 1678 tested this with a leaf blower--basically there are a cpuple of problems

1. The air has to be moving pretty fast to actually safely get the ball away from the trailer. The only way we were able to do this was by colimating it so tightly that it wouldn't be very useful anyway
2. It's only effective against shooters--if the ball is dumped into the trailer it doesn't have enough time to pick up velocity
3. The trailer has to be free to move, which means that you either need to track it or have a HUGE jet of air

Theoretically, you could solve all these problems just by moving enough air--but that might be a bit impractical.

Re: Propulsion that does not involve driving wheels
 

[SARCASM]Yes, and having an extra 50% ability to move about could be of no advantage whatsoever[/SARCASM]

The nature of the competition is to creatively solve problems to gain an advantage while maintaining compliance with the rules. If I can get going better and out-maneuver you easily, I can drive around you and dump my orbit balls into your trailer while you're still trying to get up to speed.

Who do you think more likely to win a match under this contrived situation? And who do you think is more likely to end up in Atlanta, the team that wins all its matches, or the team that doesn't?

Re: Propulsion that does not involve driving wheels
 

Our best numbers at the moment are that realistic static thrust could be on the order of 27N/kw.

The kilowatts are mechanical power. Input power to the motor is irrelevant. The peak power point on the CIM's is 337 watts but that takes 68 amps and 12V and we have neither.

A pair of CIM's operating at 40 amps each could produce about 0.4 - 0.5kw net on the shaft for a static thrust of about 10N - 13N. You can get these numbers only by matching blade size, blade angle, RPM, and torque. Motors produce maximum power when torque is 1/2 the stall torque and speed is half the no-load RPM.

I caution teams that airplane propellers are designed for flight. The blades are usually stalled until moving at considerable forward speeds. Same for most ducted fans. Large helicopter rotors may be the best bet and have the advantage of adjustable blade angle.

Re: Propulsion that does not involve driving wheels
 

Well, the GDC giveth, and the GDC taketh away.

And just like that, a little bit more room for innovation is taken away.

Re: Propulsion that does not involve driving wheels
 

The way I read that rule is that using it for -traction- I haven't read the entire topic, but you could still use a fan for propulsion, as long as you have wheels on the floor.

You can't just create a low pressure surface under your robot to keep it from moving, as someone else suggested somewhere on CD, however.

Re: Propulsion that does not involve driving wheels
 

Im really not surprised in this ruling, however, I am surprised that they used that rule to do it. I thought if they did they would use the possible damage to the field rule. but in any case, this will probably be better for the health of the nearby persons... lots of plastic dust will happen this year!

Re: Propulsion that does not involve driving wheels
 

Brad's right.

The recent ruling is that use for traction is illegal.

There are three other rulings relating to this topic, however. One governs use as goal-blocker. This is allowed. The other two govern propulsion. This use is allowed.

But using a fan or vacuum to increase normal force is out. If you show up at a regional with that sort of system, you'll need to remove it or face the inspectors with <R06> and the refs with <S04>.

Re: Propulsion that does not involve driving wheels
 

The ruling makes use as a goal blocker a rather lot more difficult, however. You'll have to mount any such goal blocking device horizontally, as any vertical inclination is going to increase your normal force. And that's going to seriously reduce the effectiveness of such a device.

Re: Propulsion that does not involve driving wheels
 

Our tests today using the 9015 FP motor direct driving an 11 x 4 prop produced 1.6 lbf of static thrust with a motor voltage of 9.6 V rms. The voltage was low due to much longer than normal wire lengths for safety reasons. The test setup was jaguars driven from the cRIO.

Scaling things to to proper voltages and a better prop we now believe that 4 lbf is readily achievable with a pair of FP motors and off the shelf 11x3 props.

With props custom designed to extract the maximum power and thrust from the FP motor, our calculations show that a pair of FP's could produce more than 8 lpf of thrust.

Re: Propulsion that does not involve driving wheels
 

just thought id comment on the stats of the RC motors. BL motors spin @ 60k RPM depending on voltage and KV rating. There are different sizes to best fit your needs. best part...the efficiency is OUT THE ROOF. My $300 NEU motor is 95% efficent :D

cant wait for the day FIRST brings brushless into the scene:D :D