Hovercraft B/C

[retired1]

While it lacks precision, 9 volts applied to a 12 volt fan would produce ABOUT 3/4 of the pressure and CFM. So that fan would not produce enough pressure to lift a 2 kg craft.
That and you will have air losses that were not planned for, so You probably should get a fan that would give you a rated p of at least 700. If you choose to use a lower voltage battery that is rechargeable, then you would need an even higher rating.
Yes, it is legal to use a 12 v fan with 9 v or less.

[Patrick Yepes]

do you think 6th - 8th graders have the ability to design and program (much less run a CNC machine tool) a propeller?

I would say absolutely yes. You would be very surprised at what they'll be able to do if you show them how the basics work. Remember, the whole point of SO is for the students to learn. Let them experiment and try it on their own. If they can't get it, give them guiding advice. Maybe let them do one part of the process and you take care of the actual machine. At any rate, I would encourage you to enable those students with a new skill, especially because you have access to such a machine.

I remember being that Junior High student, and it's the coolest thing in the world to learn something new and advanced for a SO project. It may take longer than you want and it may not be as perfect as you want, but they will have done it, and that's what matters.

I agree with you that it would be very cool for the kids to learn a new skill. I just don't think there's enough time in our current class schedule to add a basic CNC programming class. And I really doubt if any of the kids would be able to master anything but the very basic of machine moves.

On a side note, I think it would be nice to add CNC programming to the Science Olympiad. I realize it probably is a unrealistic goal but I'd love to see new people entering the trade in the not so distant future.

[chalker]

do you think 6th - 8th graders have the ability to design and program (much less run a CNC machine tool) a propeller?

I would say absolutely yes. You would be very surprised at what they'll be able to do if you show them how the basics work. Remember, the whole point of SO is for the students to learn. Let them experiment and try it on their own. If they can't get it, give them guiding advice. Maybe let them do one part of the process and you take care of the actual machine. At any rate, I would encourage you to enable those students with a new skill, especially because you have access to such a machine.

I remember being that Junior High student, and it's the coolest thing in the world to learn something new and advanced for a SO project. It may take longer than you want and it may not be as perfect as you want, but they will have done it, and that's what matters.

Note we have an official building policy that speaks directly to this: https://www.soinc.org/building_tools_policy

[Bazinga+]

Are commercial blades not allowed this year? I see a lot of people putting effort into making custom rotors, but I know there are very well made and fairly cheap blades available for just this purpose. If it is allowed what would be the advantage of making your own rotor when there are many designed with the same purpose and to provide the required lift force?

[chalker]

Are commercial blades not allowed this year? I see a lot of people putting effort into making custom rotors, but I know there are very well made and fairly cheap blades available for just this purpose. If it is allowed what would be the advantage of making your own rotor when there are many designed with the same purpose and to provide the required lift force?

The rules don't mention anything about commercial kits... and there is always General Rule #1: https://www.soinc.org/ethics_rules

[windu34]

Are commercial blades not allowed this year? I see a lot of people putting effort into making custom rotors, but I know there are very well made and fairly cheap blades available for just this purpose. If it is allowed what would be the advantage of making your own rotor when there are many designed with the same purpose and to provide the required lift force?

I think many people are having trouble trying to determine how to attach many commercial propellers to their motors.

[Bazinga+]

I think many people are having trouble trying to determine how to attach many commercial propellers to their motors.

True, but I don't see how making a custom motor would help with that. Personally, so far I have seen some success with using commercial blades with the same inner diameter as the motor, and then simply super gluing it. Its not ideal, but I haven't seen any problems with this.

[Patrick Yepes]

You can buy adapters to attach propellers to the motor shaft.

[bhavjain]

Hey Guys,

Just wondering which specific fan (a link would help!) would be sufficient to be used on a 2kg hovercraft. Not able to find one... Looking at past threads, I've come across these options:

1. http://www.digikey.com/product-search/e ... 70-1126-ND
2. http://www.digikey.com/product-detail/e ... ND/2560506
3. http://www.digikey.com/product-detail/e ... ND/4840565

Also, aren't these are brushless? If so, which of these is allowed?

Thanks.

[LIPX3]

Hey Guys,

Just wondering which specific fan (a link would help!) would be sufficient to be used on a 2kg hovercraft. Not able to find one... Looking at past threads, I've come across these options:

1. http://www.digikey.com/product-search/e ... 70-1126-ND
2. http://www.digikey.com/product-detail/e ... ND/2560506
3. http://www.digikey.com/product-detail/e ... ND/4840565

Also, aren't these are brushless? If so, which of these is allowed?

Thanks.

These fans do have brushless motors. There was a rule clarification that says you are allowed to use brushless motors if they are in a computer fan, https://www.soinc.org/official_rules_clarif . The first fan you linked would not hover. 2 kg * 9.8 m/s^2 / (0.15 m * 0.25 m) = 522.666667 pascals, and that times 4/3 equals 696.888889 pascals (The fan is 12v, but you can only use 9v batteries or less.) If you had a perfect design, you would need a 12v fan with 697 pascals of static pressure. The second fan probably wouldn't hover, as it would have an output of about 764.25 pascals of static pressure with a 9v battery, which is pretty close to 697 pascals with a perfect design. The third fan probably would hover, as it would output about 975 pascals of static pressure with a 9v battery.