Hovercraft B/C

retired1
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Re: Hovercraft B/C

Postby retired1 » October 6th, 2016, 12:16 pm

Jenn, I seriously doubt if those would put out enough pressure to lift your craft. They might work for the propulsion fan. The price is certainly right.
Go back far enough to see Chalkers calculations on the pressure required. On the craft that he designed for Wards, the fan he talks about will not lift a 2 kg craft.
Take that calculation and look at bigger (more expensive) Digi-Key fans. Our team 1 cut up a 12v dc car vac and it works well. Windu bought a air mattress infiltrator. PM him and he probably will give you the reference for it. The price is good. What ever you look at, search until you find the pressure that it will put out. You would prefer it to have a high CFM also, but less important than the PSI.

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Re: Hovercraft B/C

Postby chalker » October 6th, 2016, 2:48 pm

Having trouble interpreting the rules clarification that reads: Hovercraft 4.i. should read: "Brushless motors and integrated circuits are not permitted, unless they are an integral part of and are imbedded into a commerically available electronic or computer cooling fan." (9/12/16)

Would a fan like this one on Amazon work?

https://www.amazon.com/dp/B00XP5FEBC/re ... FCEIIA5GUX

Thanks in advance for any insight!

Jenn
It's impossible to tell whether it would work or not, since that listing doesn't provide the important spec of static pressure. But you mentioned you were having trouble interpreting the clarification. I assume you are asking whether the example you found on Amazon would be allowed. While this is not the place for official clarifications, I can unofficially say that yes, those types of fans are exactly what the language in the clarification are referring to.

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Re: Hovercraft B/C

Postby SPP SciO » October 6th, 2016, 5:18 pm

For those that have experience with NiMH batteries, what are proper safety precautions?

I have little experience with batteries. Preliminary testing shows us that the 7.2v battery packs can power our fan much more than a typical 9v can. Plus, it adds significant mass, so if it can be lifted, even better. The only issue - wiring them into circuits. They have those nice plastic connectors at the end; charging them seems safe and easy. My instinct as a teacher says it would be very unsafe to trim the leads from the battery and outfit them with alligator clips perhaps, and then clip them directly into the wall charger. Is there a better way to handle this (commercial solution) or is there some guidance on instructing some middle school students to do some safe soldering perhaps?
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Re: Hovercraft B/C

Postby kinghong1970 » October 6th, 2016, 5:45 pm

For those that have experience with NiMH batteries, what are proper safety precautions?

I have little experience with batteries. Preliminary testing shows us that the 7.2v battery packs can power our fan much more than a typical 9v can. Plus, it adds significant mass, so if it can be lifted, even better. The only issue - wiring them into circuits. They have those nice plastic connectors at the end; charging them seems safe and easy. My instinct as a teacher says it would be very unsafe to trim the leads from the battery and outfit them with alligator clips perhaps, and then clip them directly into the wall charger. Is there a better way to handle this (commercial solution) or is there some guidance on instructing some middle school students to do some safe soldering perhaps?
what about those quick connects?

Image

but curious how a 7.2v power your fan better than a typical 9v.

i know the NiMH batteries have a more steady voltage drop compared to alkali equivalent and means that you'll get the steady 7.2v until you're near the end of charge...
but if for typical runs along a 8' track, would it be an issue if the run is couple of mins at max?

Image

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Re: Hovercraft B/C

Postby retired1 » October 6th, 2016, 6:07 pm

personal opinion: When you buy NiMh batteries, get the appropriate charger from the same store. Also, you can search and find 7 cell NiMh batteries that have a nominal 8.4 volts.
When you buy the battery, be sure to find out what the plastic clip name is, also is it a male end or a female end. You can then go online and by the opposite wire end with a bare end to hook up to your motor.
A number of on line firms sell sets of normally 5 of each at a cheap price from china. 20 Ga wire is pushing it and 18 Ga would be better. You can use 10 Ga but it is overkill for the short time the motor will be on.
Note that these batteries will overcharge by at leas a full volt. This is no problem for the lift motor, but since voltage = RPM it could be a problem obtaining consistent speeds on the track.

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Re: Hovercraft B/C

Postby windu34 » October 6th, 2016, 6:13 pm

For those that have experience with NiMH batteries, what are proper safety precautions?

I have little experience with batteries. Preliminary testing shows us that the 7.2v battery packs can power our fan much more than a typical 9v can. Plus, it adds significant mass, so if it can be lifted, even better. The only issue - wiring them into circuits. They have those nice plastic connectors at the end; charging them seems safe and easy. My instinct as a teacher says it would be very unsafe to trim the leads from the battery and outfit them with alligator clips perhaps, and then clip them directly into the wall charger. Is there a better way to handle this (commercial solution) or is there some guidance on instructing some middle school students to do some safe soldering perhaps?
FOr testing purposes, I open the alligator clip slightly and push it inside the connector and grab hold of the pins that stick out. For use, I solder on the male connector to the motor and click it into the battery
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Re: Hovercraft B/C

Postby Wen » October 9th, 2016, 10:16 pm

Any recommendation on starting Hovercraft Kit for 1st time students?

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Re: Hovercraft B/C

Postby chalker » October 10th, 2016, 5:12 am

Any recommendation on starting Hovercraft Kit for 1st time students?
Ward's Sci carries the official SO approved kits: https://wardsci.com/store/content/exter ... ympiad.jsp

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Re: Hovercraft B/C

Postby retired1 » October 10th, 2016, 9:39 am

Does not look exactly like the picture that you posted. The kit contains an axial fan. Note it is not plural. It says nothing about anything else for propulsion, but the picture has a large boxed in area at the rear which probably contains a motor driven prop but is not listed in the kit. Why is there the tall mesh over the axial fan which is only a fraction of that height based on what I think I see in the picture.
For the original post, note that this is a get started "also ran" kit. It will not be seriously competitive at any state level competition. That said, the test is 50% of the final score and the craft is the other half.

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Re: Hovercraft B/C

Postby Wen » October 10th, 2016, 9:45 am

Any recommendation on starting Hovercraft Kit for 1st time students?
Ward's Sci carries the official SO approved kits: https://wardsci.com/store/content/exter ... ympiad.jsp
Thanks. I tried to order it. It says shipping within 54 days. Wonder if anything else is available for practice.


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