Hovercraft

I know that this has crossed other teams minds and so I’m just going to throw it out there. It comes down to who can build and control it better anyway…

Rule R-06 states that we must use the wheels provided to “provide traction between the ROBOT and the ARENA.” However if we throw caution to the wind and think about the idea of a hovercraft the shirt used to hover doesn’t provide traction, it reduces traction. Then fans provide thrust.

This would normally make you more easily pushed but this year everyone is going to be getting pushed around (I’ve seem the math, with wheels alone you simply cannot get more traction). This could give you more maneuverability and better control of your bot (and with four CIM’s available and a compressor I’m sure it’s doable).

Is it allowed?
Would it work?
Am I crazy?

Try it out and tell us how it goes. =

From what my team talked about, and this may not be right, but the way we interpreted it is that they would probably get you on the friction between skirt and the ground. It definitely seems like as far as moving components, they don’t really want anything touching the ground, except manipulator parts or w/e.

Of course, I’m not authority, this would be a question for the GDC when the forums go up if you really can’t find anything about it in the manual.

Also you have to remember that you are dragging a trailer, that will be pulling you down, and I think that has to have wheels, which can make it for a vulnerable bot.

From my point of view, at the start of the match, your skirt will be touching the ground and thus be considered as providing friction between the robot and the arena, in violation of <R06>.
Not to mention, I don’t see much advantage in having a hovercraft. You’re better off with rover wheels, in my opinion…you might be able to get up off the ground, butI doubt the fans you’re going to use for thrust will get you very far. Granted, I’ve never messed with many hovercrafts, so I can’t say anything on that for sure.

I think a pure hovercraft would be a silly idea. Throwing away the traction that you ARE allowed from your wheels and opting instead for an even harder to implement and control drive system doesn’t seem like the right idea.

However, using a fan to augment your acceleration and deceleration might work. The wheels can only give you a maximum of about 26.7N of acceleration1 force. If you build a fan that’s good for a few newtons of thrust2, then that can be a substantial increase in your robots straight-line handling, allowing you to outrun someone intent on dropping rocks in your trailer (and maybe even causing a bit of aerodynamic drag against them).

1: Maximum mass of robot: 54.54kg. Weight = 54.54 * 9.81 = 535N. Maximum traction: ff = uFn -> ff = 0.05 * 535N = 26.7N

2I know nothing about fans. This may very well be outside of the possibilities for a 12V fan, but it would be worth running numbers on.

First of all, crazy is relative. For instance, for the next six weeks my relatives think I’m crazy. :slight_smile:

It could, possibly, work. I figure that with wheels your maximum pushing force will be about 9 lbs (150x.06). More, of course, when you’re on the carpet at the edge of the playing field, which may become a factor.

With proper gearing and blades, it would be possible to generate at least a few pounds of thrust using the CIMs. The catch, of course, is that you will have to put a serious safety cage around your propellors.

You will also have to have your motors running at pretty much full blast the whole time you are playing, and will actively have to stop your robot, rather than just relying on wheel friction to bring it to a stop.

So while a hoverbot would be extremely cool, I suspect it would offer more disadvantages than advantages.

But perhaps, if you take the hovercraft idea and run it in reverse, you might come up with an idea to give you an edge. Let’s just say… what if your hovercraft… sucks?

Jason

P.S. R06 states that “robots MUST use rover wheels to provide traction”, so perhaps the hoverbots aren’t allowed unless they have a token roverwheel touching the ground at all times.

I personally also brought that idea to the table, before the idea of a hovercraft. But after reading R06 a few times a vacuum under the bot would be considered a “traction device” would it not?

This is a question that should be posed to FIRST, and I hope they vote in the affirmative that you can make a hovercraft.

And to pose the question as to if we can suction ourselves to the floor is another good question.

To continue this train of thought and get an idea of what would be possible. Note that neither of these would be legal:

A $2600USD model aircraft jet engine puts out 59N: http://www.trimair.com.au/index2.html. However, it is petrol powered and obviously illegal.

A $740 set of ducted fan components can put out 13-15lbs of thrust (57.9N), but uses a minimum of 3200 watts, which is 6.6 times how much power a FIRST robot can use.

You could put free rolling wheels under the skirt so that on start-up, the skirt lifts the robot off the wheels. Also you could use several of those silver motors to power a centrifugal fan similar to this one. They are commonly used in commercial hovercraft and are more efficient at this task than a vacuum or a typical fan partially because it disperses the air evenly. Then use 2 cim’s per fan for propulsion in a dual rear fan set-up.

Here’s the type of fan I’m talking about.

I’d tend to think of it as a “normal force increasing device”. Technically the vacuum would not provide any traction… it would merely increase the force acting on the wheels allowing them to provide enhanced traction.

I believe the Q&A needs to answer this one, though,

Jason

F1 buffs will get this one.

:yikes:

EDIT: Hmm, where did the picture go? Err, anyway…

I like that logic. Let me ask, to get a good vacuum would you need to touch the surface of the playing field or would you be able to make a duct that comes very close to the surface but does not touch?

I would think touching the surface would be required to gain significant benefit from it, however, it might just be a use for all those banebots/FP motors my team never finds a use for, if the Q/A determines its allowed (which i think is unlikely)

When does the Q&A open anyway?

The rules say somewhere (now with edit) that you cannot attach yourself to the arena surface.

<G29>
Arena Interaction –ROBOTS may push or react against any elements of the ARENA, provided there is no damage or disruption of the ARENA elements. With the exception of a ROBOT towing a TRAILER, ROBOTS may not grab, grasp, grapple, or attach to any ARENA structure

To finalize my discussion with myself about fans to augment your own acceleration, I found one designed for a maximum of 300 watts, which is in the range that a FRC robot can legally put out. It puts out 4 newtons while spinning at some mind-boggling RPMs. It would sound really cool spooling up.

So you’d have a drive motor running continuously at near-maximum output for 4 newtons of forward force. Maybe I’m not looking in the right places (after all, R/C fans are designed for applications where they are moving through air quickly), but that seems like it’d be too little force for a hovercraft to be effective.

You could build very light if you wanted maximum acceleration, but you’re still hauling a big trailer behind you and you’d lose pushing matches because your absolute pushing power would be lower (you’d lose your wheel traction in proportion to your weight loss).

A maximum-weight robot would get a 15% acceleration boost by using this little fan, assuming it would be a legal thing to do, you could rig a motor and gearbox to the fan, and the constant 300 watt drain wouldn’t greatly impair other robot actions.

Here is the fan: http://www.modelflight.com.au/rc_model_accessories/wemotec_micro_fan.htm

Definitely an interesting idea, but i was wondering how you were going to get past (R18) which defines the height that the trailer must be attached to the robot - 2 and 13/16ths to the center of the Trailer Hitch from the floor., doesn’t sound like it can be “floating” at different heights… which I think would occur, also they mention that it has to be rigidly attached to a fixed locations.
:yikes:

to keep going:
Thrust = mass flow * velocity
Power = (1/2) mass flow * velocity^2

For a given thrust, we could pick any combination of mass flow and velocity, but to minimize energy used, we want greater mass flow and less velocity.

max power for a single FIRST motor is 480 watts (12V * 40A). call it 500W for round numbers. So for 50 N you could do, for example, 2.5 kg/s air at 20 m/s. Now, to put this in perspective, 20 m/s = 44 mph. Seems a little high to me, but maybe not out of the question. Probably you wouldn’t get anything faster than this. Now put 2.5 kg/s of air in perspective. That’s 5.5 lb/s. Since a cubic foot of air has a mass of ~0.075 lb at standard temp and pressure, we need 73 ft^3/s. That’s 4406 ft^3/min (scfm). That’s a rather large number. Maybe not totally out of the question though.

So, unless I messed up the math, I’d guess that 50N of thrust could be achievable without violating the laws of physics or any FIRST rules, but I don’t think it would be cheap or easy…