Hovercraft B/C

[ross0814]

Does anyone know if I can get 12V out of a 9V battery? Sounds silly, I know, but I've done the static pressure calculations suggested by chalker a while ago, and the only fans that I can find all run at 12V (which is an issue considering the 9V limit in the rules). Am I misunderstanding the rules? Any help/suggestions greatly appreciated. Thank you!

R

[retired1]

Fans will work over a range of voltages. The optimum for a 12 v fan is 12v, but it will run at about 3/4 of the rpm and the static pressure on a 9 volt source.

[ross0814]

Fans will work over a range of voltages. The optimum for a 12 v fan is 12v, but it will run at about 3/4 of the rpm and the static pressure on a 9 volt source.

Yes, I know this. My problem is, the fans that provide enough static pressure to lift my hovercraft use more power. And if I calculate a higher static pressure to take into account the ¾ deficit, the only fans that are available require even MORE power. Seems like a never ending cycle.

[retired1]

Not really that circular, you calculate how much static pressure you need, go to the list of available fans and find one that 3/4 ths of the listed SP will give you what you need . Unfortunately, the higher power required will go thru batteries faster than a lower powered one. The specs for the energizer max were better than I had thought and there is one battery that is even more suitable based on specs. (I forgot the name)
Our teams went the route of a 7 cell NiMh battery which is rechargeable. Went with one store bought one and one home made one from AA sized cells.
They provide the required lift.

[antoine_ego]

The rules say we can't touch the hovercraft after the motor has been started, but does that imply indirect touching as well, i.e. a string?

[chalker]

The rules say we can't touch the hovercraft after the motor has been started, but does that imply indirect touching as well, i.e. a string?

Note that the vehicle has a max dimensions allowed. So if you have a string attached, you likely will violate the max dimensions rules since the string would have to be part of the vehicle.

[seadog]

Hi - We are new to this event and if you can help out with some of our questions, we would really appreciate it!

1) What kind of speed control is acceptable? Is a potentiometer ok?
2) Does the hovercraft need to break at the finish line? If so, do you have any suggestions on how to brake? For a stopping system, can a timer be used?
3) How is the total time divided between the two parts (written and run parts) and is there a maximum time for the written part?
4) How do you demonstrate the starting and stopping process as written in part II: Vehicle Testing (Letter j)

Thank you so much for your help!

[HandsFreeCookieDunk]

Hi - We are new to this event and if you can help out with some of our questions, we would really appreciate it!

1) What kind of speed control is acceptable? Is a potentiometer ok?
2) Does the hovercraft need to break at the finish line? If so, do you have any suggestions on how to brake? For a stopping system, can a timer be used?
3) How is the total time divided between the two parts (written and run parts) and is there a maximum time for the written part?
4) How do you demonstrate the starting and stopping process as written in part II: Vehicle Testing (Letter j)

Thank you so much for your help!

1) Yes, a potentiometer is fine. Another popular method is to partially cover the thrust fan.
2) No, the ES should have a cushion set up to stop it.
3) All that the rules say is that you will be given at least 20 minutes for the written part. You'll only have 8 minutes to do the runs, so hopefully you'll have all the rest of time for the test.
4) You just have to show the judges how you'll start and stop the motors on the hovercraft and demonstrate that it can be done safely.

[Wen]

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.

Good information. Thanks. Any recommendation on the motor for pushing in terms of.RPM range?

[sridevi]

For the speed changing is it posible to use a potentiometer