Hovercraft B/C

[windu34]

What is the part number of the motor from digi-key that suffice? We have been there and must have missed that.

Here is the link: http://www.digikey.com/product-detail/e ... ND/2560506

That is a really good looking blower! Specs are definitely above the requirement

[TheDabbingMC]

I have a question regarding the 9/12/2016 Rules Clarification. It states "Brushless motors and integrated circuits are not permitted, unless they are an integral part of and are imbedded into a commercially available electronic or computer cooling fan". Is it meant to be read as commercially available electronic fan, or as electronic cooling fan?

Thank you!

Can you clarify?
As per my knowledge, it is meant to legalize computer cooling fans that utilize brushless motors and integrated circuits inside, but only require a power supply (input to fan is only Voltage and Ground)

Thank you for the response! That was actually what I was wondering, sorry about the bad wording. I should have asked whether it was referring to commercially available electric fans in general or only those specifically built for cooling.

[sciolyqa]

Thanks for all the posts. Very helpful.

Another question. About the batteries. The dig-key cooling fans are all 12 V DC fans which will operate poorly with 9 V batteries. The SO rules, if I interpreted them correctly, limit the battery up to 9 V at any point. Could you let us know what battery(yes) you use to drive your 12 V DC fan?

[GoldDigger]

If you properly employ the skirt, shouldn't it be very easy to carry the 2kg? From reading the rules, I understood that the skirt can be in continuous contact with the base surface... Since you guys are talking about the vehicle hovering in millimeters, are you not using a skirt of does your skirt also hover? Or do you all happen to have skirts that are less than 1cm tall when inflated???

[chalker]

Thanks for all the posts. Very helpful.

Another question. About the batteries. The dig-key cooling fans are all 12 V DC fans which will operate poorly with 9 V batteries. The SO rules, if I interpreted them correctly, limit the battery up to 9 V at any point. Could you let us know what battery(yes) you use to drive your 12 V DC fan?

Most 12V fans will work just fine with a 9V battery, just not at peak performance.

[SPP SciO]

Thanks for all the posts. Very helpful.

Another question. About the batteries. The dig-key cooling fans are all 12 V DC fans which will operate poorly with 9 V batteries. The SO rules, if I interpreted them correctly, limit the battery up to 9 V at any point. Could you let us know what battery(yes) you use to drive your 12 V DC fan?

This was (is!) a major challenge for us. Look into RC battery packs, instead of those standard smoke detector size 9V. You'll get a lot more power, but also run into more problems: safety, first off, when it comes to integrating them into homemade circuits in such a way that's easy to recharge them (you'll need to find the right connectors, and do a little soldering, which is challenging for middle schoolers). Then of course, the increase in mass - it can be good (more points!) or bad (hovercraft doesn't work).

[sciolyqa]

SPP SciO,
Thanks for sharing your experience. The students had terrible experience with 9V batteries in another project and completely avoided them. The lead team member wants to use LiPo2s 7.4 v 1000mAh (or 3000mAh if necessary). For performance, I agree with his thoughts, but not without concerns.
The rules were modified once to allow using brushless motors in DC proportion devices most of which are 12 V DC fans. Although the kids understand probably all SO contestants face the same 9 V battery /12 V DC fan issue, they wish the rules would be modified again to allow 12 V power supply, unless they can miraculously find 9 V DC fans for optimization. - A Parent Mentor

[SPP SciO]

SPP SciO,
Thanks for sharing your experience. The students had terrible experience with 9V batteries in another project and completely avoided them. The lead team member wants to use LiPo2s 7.4 v 1000mAh (or 3000mAh if necessary). For performance, I agree with his thoughts, but not without concerns.
The rules were modified once to allow using brushless motors in DC proportion devices most of which are 12 V DC fans. Although the kids understand probably all SO contestants face the same 9 V battery /12 V DC fan issue, they wish the rules would be modified again to allow 12 V power supply, unless they can miraculously find 9 V DC fans for optimization. - A Parent Mentor

As stated above, the motors rated for 12V will work at 9V, and even at 7.4V. A 7.4V LiPo will spin one of those 12V fans much faster than a standard 9V battery. It's all about the right balance of power vs. weight.

As for the rules, not to be nitpick-y, but where you say "probably," the case is "definitely." It would be highly irresponsible of any event supervisor to modify rules of the tournament to allow 12V. There are some 12V power sources that can do significant harm to people and property.

[Sean_Sylvester1]

So after I built my circuit for the thrust fan (back facing fan), my 0.15W potentiometer burned out. After doing some calculations: P=IV --> P=(1A)(7.4V), I get that I need a 7.4W potentiometer. Is this right? The potentiometers I've seen rated at ~8W are upwards of $100. Is a potentiometer not a viable way to vary speed then?

Avoid using pots. When you increase he resistance on the pot, the wire gets hot like a lightbulb filament which is why it pops. That heat is energy loss, so what you want is a way to control voltage. This can be accomplished with pulse width modulation (PWM). Essentially it cycles the circuit on and off at different intervals so that it behaves like a lower or higher voltage is applied. These are also discrete circuits, meaning they are legal

[Cutinup99]

Is dry ice permitted to be used as the repulsive force to make it hover?
It doesn't say anywhere that you cant.