Hovercraft B/C

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windu34
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Re: Hovercraft B/C

Postby windu34 » October 1st, 2016, 10:57 am

So based on the fact that the craft must have a noticeable displacement off the table, skirts are required? Mine can hover about half a millimeter without a skirt and there really isn't a need for a skirt unless its required
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Re: Hovercraft B/C

Postby sciolyFTW_aku » October 1st, 2016, 11:52 am

So based on the fact that the craft must have a noticeable displacement off the table, skirts are required? Mine can hover about half a millimeter without a skirt and there really isn't a need for a skirt unless its required
Hello,

A half a millimeter seems really small... but if you push down on your hovercraft, then release it, and it comes back up again, you should be good :) .

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Re: Hovercraft B/C

Postby sciolyFTW_aku » October 1st, 2016, 11:54 am

To get a good score do you need to have a fast Time Score and a small Mass score?
To elaborate on the time score: the goal is for your device's time to be as close as possible to the target time, hence you will need to design and test your device so that you can modify it for all of the allowable target times (see the rules).
Hello,

Sorry to double post, but does anyone have any ideas for adjusting the time of the hovercraft?

Thanks,
sciolyFTW_aku
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Re: Hovercraft B/C

Postby Zioly » October 1st, 2016, 12:10 pm

To get a good score do you need to have a fast Time Score and a small Mass score?
To elaborate on the time score: the goal is for your device's time to be as close as possible to the target time, hence you will need to design and test your device so that you can modify it for all of the allowable target times (see the rules).
Hello,

Sorry to double post, but does anyone have any ideas for adjusting the time of the hovercraft?

Thanks,
sciolyFTW_aku
At first, I thought adjusting the weight of the Hovercraft would be the most effective way to control the Hovercraft's speed. Then, I realized that for the National competition, this is not a great idea, as you'd be losing to the people who maxed their craft's weight at 2000 grams. However, for Regionals and States, it could be viable. In the long run, it's probably best to adjust the fan speed. From this, my friend suggested a speed control chip, but (I believe) those aren't allowed. If your Hovercraft has only one fan, and you have an airflow director, you could change the amount of air that goes towards the back. Finally, the most viable solution I've thought of for two fanned craft's is just switching the batteries, although I'm not sure how consistent or inconsistent that could be.

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Re: Hovercraft B/C

Postby windu34 » October 1st, 2016, 12:27 pm


Hello,

Sorry to double post, but does anyone have any ideas for adjusting the time of the hovercraft?

Thanks,
sciolyFTW_aku
You are going to want to use a variable resistor or a ducting system to constrict airflow
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Re: Hovercraft B/C

Postby sciolyFTW_aku » October 1st, 2016, 1:10 pm

At first, I thought adjusting the weight of the Hovercraft would be the most effective way to control the Hovercraft's speed. Then, I realized that for the National competition, this is not a great idea, as you'd be losing to the people who maxed their craft's weight at 2000 grams. However, for Regionals and States, it could be viable. In the long run, it's probably best to adjust the fan speed. From this, my friend suggested a speed control chip, but (I believe) those aren't allowed. If your Hovercraft has only one fan, and you have an airflow director, you could change the amount of air that goes towards the back. Finally, the most viable solution I've thought of for two fanned craft's is just switching the batteries, although I'm not sure how consistent or inconsistent that could be.

Sorry for the wall of text.
You are going to want to use a variable resistor or a ducting system to constrict airflow
Thank you both for the advice. But, how would you be able to use an airflow director? Do you mean the air is sent through a tube, which is then split into smaller tubes and you can control which tubes are open, or by changing the size of the outer exit of the large tube?

Thanks,
sciolyFTW_aku
B-)

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Re: Hovercraft B/C

Postby windu34 » October 1st, 2016, 1:37 pm

At first, I thought adjusting the weight of the Hovercraft would be the most effective way to control the Hovercraft's speed. Then, I realized that for the National competition, this is not a great idea, as you'd be losing to the people who maxed their craft's weight at 2000 grams. However, for Regionals and States, it could be viable. In the long run, it's probably best to adjust the fan speed. From this, my friend suggested a speed control chip, but (I believe) those aren't allowed. If your Hovercraft has only one fan, and you have an airflow director, you could change the amount of air that goes towards the back. Finally, the most viable solution I've thought of for two fanned craft's is just switching the batteries, although I'm not sure how consistent or inconsistent that could be.

Sorry for the wall of text.
You are going to want to use a variable resistor or a ducting system to constrict airflow
Thank you both for the advice. But, how would you be able to use an airflow director? Do you mean the air is sent through a tube, which is then split into smaller tubes and you can control which tubes are open, or by changing the size of the outer exit of the large tube?

Thanks,
sciolyFTW_aku
For simplicity's sake, I would change the size of the outer exit, but I suppose both methods could work
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Re: Hovercraft B/C

Postby retired1 » October 1st, 2016, 2:34 pm

Another opinion.
I think that people would have problems with using only one fan with the wild combination of distances and times = speeds.It will take a rather large fan to be able to both lift and propel the heavy craft at the max speed. It is a lot simpler to have 2 fans. The lift fan is a constant. whatever size and voltage that will do the job. The propulsion fan needs to either control the RPM or the amount of air diverted. The amount of air diverted will depend on the RPM of that fan. A fully charged NiMh or NiCd or Li ion or poly has a vastly different initial voltage than one that has run for a while. If you look at the curves, you will find that after the initial voltage drop that the voltage tends to steady out. (for longer than I thought). That is also dependent on the electrical draw of the motor. If it is a high amperage motor (watts) then the curve will be less steady. So a method to control the voltage is nice.

A huge difference in this event is the apparent allowance of using a full bottom covering rather than just edge skirts. This amounts to the craft being fully supported by the "bag" rather than a flow of air. This should require a much smaller lift fan.

In earlier blog, Chalker said that he could not get edge skirts to work. It is not easy, but is doable. It took us about 8 tries to get it. It does require a stouter craft than the one he designed for the only certified SO vendor.

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Hovercraft Division B

Postby MrGood » October 1st, 2016, 3:05 pm

So I've been working on my hovercraft design for the event, and is wondering if anyone has tips on building an air vent that will provide enough air for the hovercraft to reach a few centimetres off of the ground (2-4) in order to have less friction on the base so that my hovercraft can build enough momentum.

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Re: Hovercraft B/C

Postby windu34 » October 1st, 2016, 3:42 pm

Another opinion.
I think that people would have problems with using only one fan with the wild combination of distances and times = speeds.It will take a rather large fan to be able to both lift and propel the heavy craft at the max speed. It is a lot simpler to have 2 fans. The lift fan is a constant. whatever size and voltage that will do the job. The propulsion fan needs to either control the RPM or the amount of air diverted. The amount of air diverted will depend on the RPM of that fan. A fully charged NiMh or NiCd or Li ion or poly has a vastly different initial voltage than one that has run for a while. If you look at the curves, you will find that after the initial voltage drop that the voltage tends to steady out. (for longer than I thought). That is also dependent on the electrical draw of the motor. If it is a high amperage motor (watts) then the curve will be less steady. So a method to control the voltage is nice.

A huge difference in this event is the apparent allowance of using a full bottom covering rather than just edge skirts. This amounts to the craft being fully supported by the "bag" rather than a flow of air. This should require a much smaller lift fan.

In earlier blog, Chalker said that he could not get edge skirts to work. It is not easy, but is doable. It took us about 8 tries to get it. It does require a stouter craft than the one he designed for the only certified SO vendor.
Why would it be advantageous to use a full bottom skirt? Your speed would be effected much more by the surface texture of the table and the friction coefficient plays a major role and it is important to keep it minimal for the best competition-to-competition consistency. I understand it is much easier to implement, but the costs in performance are quite vast
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