Hovercraft B/C

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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

JennJ wrote: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

SPP SciO wrote: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

SPP SciO wrote: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

Wen wrote: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

chalker wrote:
Wen wrote: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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Re: Hovercraft B/C

Postby SPP SciO » October 10th, 2016, 10:01 am

Wen wrote:
chalker wrote:
Wen wrote: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.


Just look at the materials it comes with - Ordering Information: Kit includes On/Off Switch, 9V Battery Connector, Motor; 6V-12V, Steel Battery Holder, Self-Adhesive Clip, Plastic Propeller, Produce Bags, Styrofoam Tray, Mesh Squares, Insulated Wire, 9V Batteries, Wooden Dowels, Nylon Cable Ties, Transparent Tape, Utility Knife, and Axial Fan.


That's what you'll get for $107*. You pay the premium to have it all packaged together (and presumably get some sort of instruction sheet) but there's a good chance that between school and home, you have a lot of these items anyway, and a trip to a dollar store or hardware store can fill in the rest. As previously stated, this is a great starting point, and students will be able to build a functional, competition-ready hovercraft. Hopefully they'll find ways to improve on it the more they test it.

*Chalker, can you explain how this price point is set? I assume there's some partnership between Ward's and SO Inc., and this is good business for all parties, but, $107?! Frankly it seems like it's $7 worth of stuff and a $100 packaging fee. If you're contractually obligated not to discuss this, I get it, but all of the online kits seem dramatically overpriced.
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Re: Hovercraft B/C

Postby Wen » October 10th, 2016, 10:19 am

SPP SciO wrote:
Wen wrote:
chalker wrote:
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.


Just look at the materials it comes with - Ordering Information: Kit includes On/Off Switch, 9V Battery Connector, Motor; 6V-12V, Steel Battery Holder, Self-Adhesive Clip, Plastic Propeller, Produce Bags, Styrofoam Tray, Mesh Squares, Insulated Wire, 9V Batteries, Wooden Dowels, Nylon Cable Ties, Transparent Tape, Utility Knife, and Axial Fan.


That's what you'll get for $107*. You pay the premium to have it all packaged together (and presumably get some sort of instruction sheet) but there's a good chance that between school and home, you have a lot of these items anyway, and a trip to a dollar store or hardware store can fill in the rest. As previously stated, this is a great starting point, and students will be able to build a functional, competition-ready hovercraft. Hopefully they'll find ways to improve on it the more they test it.

*Chalker, can you explain how this price point is set? I assume there's some partnership between Ward's and SO Inc., and this is good business for all parties, but, $107?! Frankly it seems like it's $7 worth of stuff and a $100 packaging fee. If you're contractually obligated not to discuss this, I get it, but all of the online kits seem dramatically overpriced.


Oh, it's more than that. They charge another $18+ shipping and $10+ tax. That is why I have been hesitating in ordering it. I also looked over the list. What I'm not sure about are Motor, Plastic Propeller, Axial Fan: what kind should I buy if I go buy them myself? Also Mesh Squares, what are they for? Wooden Dowels: Balsa wood? How thick? A design that shows what goes where will be helpful.

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Re: Hovercraft B/C

Postby SPP SciO » October 10th, 2016, 10:39 am

Wen wrote: Oh, it's more than that. They charge another $18+ shipping and $10+ tax. That is why I have been hesitating in ordering it. I also looked over the list. What I'm not sure about are Motor, Plastic Propeller, Axial Fan: what kind should I buy if I go buy them myself? Also Mesh Squares, what are they for? Wooden Dowels: Balsa wood? How thick? A design that shows what goes where will be helpful.


The motor is just a typical DC motor; the little metal cylinder with a shaft and two leads or wire tabs. Radio Shack sells them individually for $2-3 but if you ask the technology/science teachers at your school, they may just have a whole bin of them sitting around. The plastic propeller is literally nothing more than a twisted piece of plastic; you can buy multi packs online if you want to test out a variety, but they're also not hard to make - cut a strip of some thin rigid plastic, punch a hole through the middle with a hot nail, and if you warm it up over a flame for a few seconds you can twist it into a propeller shape. I believe the axial fan that comes with the kit is a small computer cooling fan. If you have no idea where to salvage one, check the links to DigiKey a few pages back in this thread. We wound up testing a few, and were able to find one that can lift the max weight for under $30 - but a smaller one, for much less than that, will do just fine. Mesh squares are for compliance with rule 4.e - the propellers must be shielded. Keep your eyes peeled and you'll find something lying around suitable for that (a pair of scissors may be needed). The dowel is for compliance with 4.g - 1/4" or more, for triggering the photogates. 1/4" is pretty standard "dowel size" so again, just look around for one, or pop in to the nearest dollar store.

As for how to put it altogether, you could probably reverse engineer it from the Ward's kit picture. Or, better yet, check out some of the videos on YouTube (there were links either in this thread or the Hovercraft thread in General Chat) and you'll see a hovercraft assembled from start to finish.
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Re: Hovercraft B/C

Postby retired1 » October 10th, 2016, 11:26 am

Your figures $135 +/- for the kit that is a starter only.
Our team 1 is using a 12V car vac bought at a flea market for $5. I just bought team 2 a top of the line Digi_Key axial fan that is really nice for $40 including tax and shipping. You can go online and buy appropriate push motors for under $10. You can find a number of props for under $5. You can get switches on line cheaper than radio shack.Add foam board or wood and plastic sacks and you are ready to build a competitive craft. Team 2 for about $70 including a couple of extras for a competitive craft. Sure beats $135 in my book.
If your team competed in Maglev, you should have props and motors Plus ?

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Re: Hovercraft B/C

Postby Unome » October 10th, 2016, 11:30 am

SPP SciO wrote:
Wen wrote: Oh, it's more than that. They charge another $18+ shipping and $10+ tax. That is why I have been hesitating in ordering it. I also looked over the list. What I'm not sure about are Motor, Plastic Propeller, Axial Fan: what kind should I buy if I go buy them myself? Also Mesh Squares, what are they for? Wooden Dowels: Balsa wood? How thick? A design that shows what goes where will be helpful.


The motor is just a typical DC motor; the little metal cylinder with a shaft and two leads or wire tabs. Radio Shack sells them individually for $2-3 but if you ask the technology/science teachers at your school, they may just have a whole bin of them sitting around. The plastic propeller is literally nothing more than a twisted piece of plastic; you can buy multi packs online if you want to test out a variety, but they're also not hard to make - cut a strip of some thin rigid plastic, punch a hole through the middle with a hot nail, and if you warm it up over a flame for a few seconds you can twist it into a propeller shape. I believe the axial fan that comes with the kit is a small computer cooling fan. If you have no idea where to salvage one, check the links to DigiKey a few pages back in this thread. We wound up testing a few, and were able to find one that can lift the max weight for under $30 - but a smaller one, for much less than that, will do just fine. Mesh squares are for compliance with rule 4.e - the propellers must be shielded. Keep your eyes peeled and you'll find something lying around suitable for that (a pair of scissors may be needed). The dowel is for compliance with 4.g - 1/4" or more, for triggering the photogates. 1/4" is pretty standard "dowel size" so again, just look around for one, or pop in to the nearest dollar store.

As for how to put it altogether, you could probably reverse engineer it from the Ward's kit picture. Or, better yet, check out some of the videos on YouTube (there were links either in this thread or the Hovercraft thread in General Chat) and you'll see a hovercraft assembled from start to finish.

Expanding on the point about "propellers must be shielded;" this rules presumably comes from MagLev. Not sure how long you've been around, but MagLev was basically scrapped due to safety issues. I believe chalker mentioned somewhere that Hovercraft is basically MagLev with the dangerous parts removed.
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