Hovercraft 2016-2017

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Re: Hovercraft 2016-2017

Postby Zioly » July 31st, 2016, 1:03 pm

DoctaDave wrote:
windu34 wrote:Hey so I'm new to physics lab events and was wondering what to expect as far as the math goes. What should I expect?


When I competed in compound machines everything was algebra based. I do remember at an invite we got a well written test and there was a calculus based question, but it only required finding the derivative of a polynomial so it wasn't anything crazy. But algebra based physics can still be really difficult. Just take a look at the f=ma tests which require no calculus.

I never competed for compound machines at nats but I would not expect much calculus there either.


Yeah, I guess it would depend on the ES. If I were a physics professor volunteering as the ES, I probably wouldn't throw calculus questions into a test that could be taken by 6th graders, but hey, we're all different. On the other hand, I heard Crave the Wave had calculus last year? And optics will have it next year? I have no idea. I've never looked into either of those events.
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Re: Hovercraft 2016-2017

Postby Unome » July 31st, 2016, 1:07 pm

Zioly wrote:
DoctaDave wrote:
windu34 wrote:Hey so I'm new to physics lab events and was wondering what to expect as far as the math goes. What should I expect?


When I competed in compound machines everything was algebra based. I do remember at an invite we got a well written test and there was a calculus based question, but it only required finding the derivative of a polynomial so it wasn't anything crazy. But algebra based physics can still be really difficult. Just take a look at the f=ma tests which require no calculus.

I never competed for compound machines at nats but I would not expect much calculus there either.


Yeah, I guess it would depend on the ES. If I were a physics professor volunteering as the ES, I probably wouldn't throw calculus questions into a test that could be taken by 6th graders, but hey, we're all different. On the other hand, I heard Crave the Wave had calculus last year? And optics will have it next year? I have no idea. I've never looked into either of those events.

Based on Simple Machines experience: expect easy stuff from professors (so make sure you know it very well) but there are definitely times where you'll get a good test and have to actually think your way through problems. I don't know much about kinematics but it seems mostly the same as what we did in Simple Machines; just take the formulas and apply them to the problem.
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Re: Hovercraft 2016-2017

Postby Adi1008 » July 31st, 2016, 1:15 pm

Unome wrote:
Zioly wrote:
DoctaDave wrote:
When I competed in compound machines everything was algebra based. I do remember at an invite we got a well written test and there was a calculus based question, but it only required finding the derivative of a polynomial so it wasn't anything crazy. But algebra based physics can still be really difficult. Just take a look at the f=ma tests which require no calculus.

I never competed for compound machines at nats but I would not expect much calculus there either.


Yeah, I guess it would depend on the ES. If I were a physics professor volunteering as the ES, I probably wouldn't throw calculus questions into a test that could be taken by 6th graders, but hey, we're all different. On the other hand, I heard Crave the Wave had calculus last year? And optics will have it next year? I have no idea. I've never looked into either of those events.

Based on Simple Machines experience: expect easy stuff from professors (so make sure you know it very well) but there are definitely times where you'll get a good test and have to actually think your way through problems. I don't know much about kinematics but it seems mostly the same as what we did in Simple Machines; just take the formulas and apply them to the problem.


I don't think I've ever seen anything in scioly that requires calculus; I think it's kind of an unwritten rule to not include it. Also, as DoctaDave said, physics (and pretty much everything) can be really hard even without calculus - just look at the AAPT F=ma exam!
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Re: Hovercraft 2016-2017

Postby Zioly » July 31st, 2016, 2:09 pm

Adi1008 wrote:I don't think I've ever seen anything in scioly that requires calculus; I think it's kind of an unwritten rule to not include it. Also, as DoctaDave said, physics (and pretty much everything) can be really hard even without calculus - just look at the AAPT F=ma exam!


What!? All this time, my friend who is doing hex-a-jump math, has been bragging about how useful his calculus knowledge was for Crave the Wave! I have lost all respect. :evil: (Just kidding)
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Ecology: 9th
Hovercraft: 14th
Scrambler: 29th (with a failed run too ;))


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Re: Hovercraft 2016-2017

Postby windu34 » July 31st, 2016, 9:12 pm

Thanks for all the responses! As far as previous nationals tests have been for compound machines, wind power, its about time, etc physics tests, has calculus ever been present (or helpful to know by the competitor.
Additionally, the topics on the hovercraft rules (kinematics, kinetic energy, etc) are conventionally physics-math problems, but I suppose there are history aspects that could be asked. Thoughts? Thanks
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Re: Hovercraft 2016-2017

Postby Adi1008 » July 31st, 2016, 9:28 pm

windu34 wrote:Thanks for all the responses! As far as previous nationals tests have been for compound machines, wind power, its about time, etc physics tests, has calculus ever been present (or helpful to know by the competitor.
Additionally, the topics on the hovercraft rules (kinematics, kinetic energy, etc) are conventionally physics-math problems, but I suppose there are history aspects that could be asked. Thoughts? Thanks


I've never, ever seen any calculus on a test at nationals*. I don't think you should expect to see any.

As for the types of questions in Hovercraft - I really hope they're (very hard, akin to f=ma level if not a bit harder) physics/math problems, but I think there'll probably be a few history questions too T_T

*The only Division C study event I've ever done at nationals was Astronomy, but I'm pretty sure there's like an unwritten rule not to make calculus required to solve any questions. In Division B crave the wave, there was (obviously) no calculus
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Re: Hovercraft 2016-2017

Postby retired1 » August 3rd, 2016, 9:44 am

Jeff or Chalker,
Opinion please. I have a small speed control unit. It can not be programmed like many ESC's can. It is basically a rheostat with an off position on the knob--BUT it has 2 tiny chips that I have zero idea what they do. Would this unit be considered an integrated circuit per 3.j. of the trial event rules???
I am not an electronics type person, so I have no idea what constitutes an IC.

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Re: Hovercraft 2016-2017

Postby chalker » August 3rd, 2016, 5:28 pm

retired1 wrote:Jeff or Chalker,
Opinion please. I have a small speed control unit. It can not be programmed like many ESC's can. It is basically a rheostat with an off position on the knob--BUT it has 2 tiny chips that I have zero idea what they do. Would this unit be considered an integrated circuit per 3.j. of the trial event rules???
I am not an electronics type person, so I have no idea what constitutes an IC.


It's hard to say for sure, but they likely are ICs. Do they have anything printed on them? If so, do a google search for what's written on them and you might find out more details. Do they have multiple wires / pins going into them? If so, they are almost definitely ICs. Typically the only thing that looks like a 'chip' but isn't an IC is a surface mount resistor, which you can see pictures of here: https://www.google.com/search?q=surface ... 4Q_AUIBigB

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Re: Hovercraft 2016-2017

Postby windu34 » August 19th, 2016, 5:15 pm

I have found it is incredibly difficult to find brushed ducted fans online. The average thrust is something like 500g which is clearly not sufficient for the job. 2kg is going to be difficult to lift based on the availability of fans that I have found. Am I looking for fans the wrong way or is this consist with the rest of you guy's research?
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Re: Hovercraft 2016-2017

Postby chalker » August 20th, 2016, 9:02 am

windu34 wrote:I have found it is incredibly difficult to find brushed ducted fans online. The average thrust is something like 500g which is clearly not sufficient for the job. 2kg is going to be difficult to lift based on the availability of fans that I have found. Am I looking for fans the wrong way or is this consist with the rest of you guy's research?


Yes, you are indeed looking at them wrong. I spent the past few weeks designing and testing the parts for the official Ward's Sci kit that will be available soon. In doing that, I looked at a variety of fans and ended up settling on a cooling fan like what you'd see as part of your computer power supply. There are a lot of types available, but the specific one I tried out is this one: http://www.digikey.com/product-search/e ... 70-1126-ND

The KEY stat to look at when you are trying to select a fan is the static pressure (for the example fan it's 300.4 Pascals). In order to levitate the device, the fan(s) need to be able to provide enough pressure under the device to counteract the weight of the device (i.e. pressure is force per unit area). Note it's force not mass, so you need to use the value of Earth's Gravity (9.8 m/s^2) in calculations.

So for example, to levitate a 250 g device with a footprint of 15x25 cm you need: 0.250 kg * 9.8 m/s^2 / (0.15 m x 0.25 m) = 65 pascals (try it yourself: https://www.google.com/?gws_rd=ssl#q=0. ... m+x+0.25+m) ) Keep in mind though that assumes perfect conditions and no losses at all.

A device with max mass of 2kg would require a minimum of 8 times that, or 520 pascals. Digikey has fans like the one I indicated about that handle 1,300 pascals for $27, which with the proper design should be able to handle a max spec device.

Note I'm not saying you have to go with this specific type of fan or design, as all fans have a certain static pressure rating. Just trying to help everyone understand the physics involved.

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Re: Hovercraft 2016-2017

Postby windu34 » August 20th, 2016, 1:42 pm

chalker wrote:
windu34 wrote:I have found it is incredibly difficult to find brushed ducted fans online. The average thrust is something like 500g which is clearly not sufficient for the job. 2kg is going to be difficult to lift based on the availability of fans that I have found. Am I looking for fans the wrong way or is this consist with the rest of you guy's research?


Yes, you are indeed looking at them wrong. I spent the past few weeks designing and testing the parts for the official Ward's Sci kit that will be available soon. In doing that, I looked at a variety of fans and ended up settling on a cooling fan like what you'd see as part of your computer power supply. There are a lot of types available, but the specific one I tried out is this one: http://www.digikey.com/product-search/e ... 70-1126-ND

The KEY stat to look at when you are trying to select a fan is the static pressure (for the example fan it's 300.4 Pascals). In order to levitate the device, the fan(s) need to be able to provide enough pressure under the device to counteract the weight of the device (i.e. pressure is force per unit area). Note it's force not mass, so you need to use the value of Earth's Gravity (9.8 m/s^2) in calculations.

So for example, to levitate a 250 g device with a footprint of 15x25 cm you need: 0.250 kg * 9.8 m/s^2 / (0.15 m x 0.25 m) = 65 pascals (try it yourself: https://www.google.com/?gws_rd=ssl#q=0. ... m+x+0.25+m) ) Keep in mind though that assumes perfect conditions and no losses at all.

A device with max mass of 2kg would require a minimum of 8 times that, or 520 pascals. Digikey has fans like the one I indicated about that handle 1,300 pascals for $27, which with the proper design should be able to handle a max spec device.

Note I'm not saying you have to go with this specific type of fan or design, as all fans have a certain static pressure rating. Just trying to help everyone understand the physics involved.

I looked over the majority of the fans on that website including the one you linked and even though there are only 2 leads, the motor itself is brushless. This opens up a lot of questions assuming I am correct. How am I to discern between brushed and brushless fans if there are only 2 leads? These fans likely have integrated circuits inside the housing. The majority of competitors will likely use brushless fans without even knowing it. Additionally, I highly doubt most event supervisors will know how to check and identify a brushless fan other than from the characteristic 3 leads or by an ESC.
For example, this fan has 2 leads, yet when I looked into the datasheet, it was stated as brushless:
http://www.digikey.com/product-detail/e ... ND/4840565
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Re: Hovercraft 2016-2017

Postby retired1 » August 20th, 2016, 6:17 pm

I did not see where it was brushless, but it does state that it has PWM speed control which would make it an IC device.
I assume that the loss of some air from the bottom would lower the 1300 p by a fair amount. Also the available battery voltage will drop the 1300 down to 800 to 900 depending on the batteries used. It draws a lot of current, so battery selection will be important.
I guess that a person could use a total bag and then there would be no losses. It would just require a bit bigger push fan.
Our team has one with conventional bags that works, but it took a lot of failures.

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Re: Hovercraft 2016-2017

Postby chalker » August 20th, 2016, 8:45 pm

windu34 wrote:I looked over the majority of the fans on that website including the one you linked and even though there are only 2 leads, the motor itself is brushless. This opens up a lot of questions assuming I am correct. How am I to discern between brushed and brushless fans if there are only 2 leads? These fans likely have integrated circuits inside the housing. The majority of competitors will likely use brushless fans without even knowing it. Additionally, I highly doubt most event supervisors will know how to check and identify a brushless fan other than from the characteristic 3 leads or by an ESC.
For example, this fan has 2 leads, yet when I looked into the datasheet, it was stated as brushless:
http://www.digikey.com/product-detail/e ... ND/4840565


Hmmm.. very interesting indeed. I hadn't dug into this that thoroughly and assumed they weren't brushless since there isn't any IC or ESC evident in the design of them. As the rules have already gone to print, we might have to consider issuing an FAQ about this. The intent is definitely to allow fan modules such as this. The prohibition on IC's and brushless motors really go hand in hand with ensuring that the designs don't end up being extremely sophisticated (and expensive) computer controlled things (i.e. as a way to try to level the playing field and keep the costs down). Thanks for pointing this out. I think it's safe to say you should go ahead and consider using fans like this in the design if you want to.

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Re: Hovercraft 2016-2017

Postby retired1 » August 21st, 2016, 10:58 am

A word of caution-- The Sunon site states that the operating voltage is 10.2 to 12.6.
The performance chart shows that 10.2 volts drops the static pressure from 5.2 to 4.0. (a 23% reduction)
I would expect a large drop off using either 7.4 v LiPo or 8.4V NiMh. If linear, 3.5"H2O. (or about 680p) (ussing 8 V for calculation)
That assumes that it will work at all at the out of range voltage as somewhere it listed the 10.2v as "starting voltage". I do not know if this is based on the bottom of the range or possibly it will not work at all. Remember that this is a PWM controlled motor.
I have sent a query to Sunon and will post whatever they respond with.

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Re: Hovercraft 2016-2017

Postby chalker » August 21st, 2016, 11:49 am

Keep in mind that you don't have to get those particular fans from that particular website. There are lots available, I just wanted to point everyone in the right direction. FYI, here is a link to a picture of a fully assembled, functional and in spec hovercraft which is what you can build with the Ward's Sci kit that will be coming out in a few weeks (I can't seem to figure out how to actually embed the picture like I used to be able to). It will be available here eventually (hint hint): https://wardsci.com/store/content/exter ... ympiad.jsp

https://1drv.ms/i/s!AiDNRgPxV7d-hNFkg7Uw4NYrV3yVuQ

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