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