Hovercraft

[minisimon]

This question has been vexing me as well. My good friend (http://en.wikipedia.org/wiki/Propeller) tells me that propellers max out around 80% efficiency. I'm afraid that we won't get anywhere near an optimum prop, so let's assume 10% efficiency with 300W of CIM, yielding 30 W. When your robot is moving at 2 m/s, 30 W should translate to 15 N, about 3 lbs. If you power your fan or fans with 2 CIMS, you get 6 lbs of thrust, which would make a nice adder to the 7.5 lbs you get from traction.

Now, if someone who knew what they were doing made the prop a mere 30% efficient, then they would have an additional 18lbs of thrust; enough to push anyone around.

Unfortunately, I have no idea where you would purchase or how you would design this propeller. There are some big RC planes out there, but I can't find much information on thrust produced or efficiency. Anybody have any leads?

[ryanking09]

Originally Posted by ExarKun666

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.

This one is for EXARKUN666... You posted somewhere that you were unsure of the numbers that were used in the "LUNACY: initial game layout" in chapter 7. I realized that the <=7 on the carts and the 13-20 mean
the 13-20 is starting count for the moon rocks for that station 20 is max and if u load moon rocks on your robot before start, which max is 7, then that explains where u get the 13 moon rocks at start from, because you would have taken 7 from 20 to put on robot. And the <=4 is indicating that you will have 4 or less of the empty cells at start. I believe that you can load moon rocks and/or empty cells on your robot before start, but i don't see why you would put empty cells on your robot before start.

this is out of context from this thread but i could not find the thread that u originally asked about this so i quoted u here and posted here. Not to get off topic.

[eNyoron]

I think everybody's best bet as of now would just be to check out some hobby shops to get a look at propellers used for RC planes, copters, airboats or anything similar.

[scirobotics]

lol, i think it will be more like a game of air hockey

[Prontopwnage]

hey you guys, your thinking to hard...
You could do the opposite and get more grip... Like that model car that can go on the ceiling! I don't know if that would work... What do you guys think?

[cj.reeves]

is the coeficient of friction independent of surface area under the present conditions

[n_ambrogi013]

i think that someone already discussed earlier in this thread using a fan to generate downforce, effectively increasing the normal force on the wheels.

my question is, how would you calculate the amount of suction force that a fan can generate against a solid surface like the playing field? using drive motors to power a fan is really only worth it if there is a significant traction increase.

also, is it legal to generate downforce with a fan?

[scirobotics]

it is illigal to genarate downforce with a fan

[DonRotolo]

Originally Posted by Prontopwnage

hey you guys, your thinking to hard...
You could do the opposite and get more grip... Like that model car that can go on the ceiling! I don't know if that would work... What do you guys think?

I think you're not thinking hard enough, since you asked.

Originally Posted by cj.reeves

is the coeficient of friction independent of surface area under the present conditions

Yes, as coefficient of friction is a property of the interaction of two surfaces. But I think you want to know about pushing power, which theoretically remains the same because a larger area means a smaller force per unit area, but in reality a larger surface contact area means a very slightly increased pushing power.

Originally Posted by scirobotics

it is illigal to genarate downforce with a fan

Can you quote a rule please? Or is this speculation?

[excel2474]

I've built hovercrafts before and let me tell you that by time your robot is all said and done, you won't be able to hover. I mean, it could be possible, but that would require so much power that it's just not plausible. I just seriously doubt that you could build a hover craft and efficiently complete the mission.

[Devo1098]

Originally Posted by excel2474

I've built hovercrafts before and let me tell you that by time your robot is all said and done, you won't be able to hover. I mean, it could be possible, but that would require so much power that it's just not plausible. I just seriously doubt that you could build a hover craft and efficiently complete the mission.

I'd like to see one of your hovercraft's, they must be crap. out of cim motors and first batteries i've built a hover craft that moves me around, and I'm not talking a hovercraft in the shape of a circle with a shop vac on the blowing port. a full blown movable steering hovercraft. (two cim motors on car radiator fans for lift)

after several years of building model hovercraft's more or less the exact same size as a first robot I'm positive you could lift a decent weight (i wouldn't do 150, it'll make it hard to steer) and move.

on this low traction force with a well maneuverable hovercraft and a driver who actually knows what their doing, that team could out run, out push and plainly out preform the wheels. in this low traction surface i have no doubt a 60lbs hovercraft with a a 20" fan could push a 150lbs robot with those wheels.

driving is sorta an art, like drifting, everybody believes they can do it, because it looks easy, but really once behind the wheel the most frequent thing done is a spin out or end swap.

now i do think it would be dumb to have a complete hovercraft, with the little traction, you want all you can get....not less. my idea is to have a standard chassis, but have some thrust fans with rudders, to get you up to speed faster improve braking and turning. are there any rules that this would violate?

[Woody1458]

If you wish to make a suction device tell me when you find a Unobtanium retailer because that would require something that both makes an airtight seal and has a µ=0

[EStokely]

Originally Posted by Woody1458

If you wish to make a suction device tell me when you find a Unobtanium retailer because that would require something that both makes an airtight seal and has a µ=0

Well lets not assume you need 100% effcientcy.

Any lowering of air pressure under the machine will provided additional Normal Force. So if you had skirts that are within 1/2 inch you would get a reduced pressure when you started vacuuming air out of the area.
Have I done the numbers? no...
Is there a prototype in the works? Yes.

It may not provided enough of a difference to use but I can't dismiss it out of hand.

I suspect a week before we decide yes or no on the idea.

[M. Gildner]

just a thought, but a hovercraft would provide a defensive advantage.
The fan could in theory push cells and rocks away from the trailer.

[Sean Raia]

I dont think that the fan in the back would be a good propeller on its own, but used with the wheels it may give a minor advantage.