Hovercraft B/C

[CaptainJackSparrow]

Keep this in mind... The weight score is proportional to the heaviest vehicle with a successful run, so unless you you are very neck and neck with another team, maxing out at 2000g may not even matter much, and just expose the team to a possible penalty (depending on a judges interpretation). Also, 10 grams of weight corresponds to roughly 0.1 second of time delta, which is also in the noise.... our team's vehicle weighed in about 10 grams more at run time than at impound. Maybe the kids added some duct tape when they strapped the batteries on? Who knows. But at states they are going to play it safe and allow for a margin of error on the scales. Our regional does not distribute the hovercraft scoring breakdown, so they really don't know how close things were, or whether tenths of a point came into play.

YMMV. Good luck!

Question about the scoring rule 6d. Our team has a hovercraft that works at 2 kg. To ensure full credit for the MS, there's a small container of sand ballast - the strategy is to adjust that mass at impound, to make sure the vehicle registers 2,000.0 grams on the supervisor's scale. Rule 5g leaves the possibility open that this mass check will be done right before a run. Re-reading the rule, I'm worried that they'd have 2,001 grams, have to remove a gram of sand before the run, and get the 0.7x penalty.

So to summarize, 1) has anyone used this strategy successfully, and if so, was the measurement during a pre-competition impound, or right before the run?
2) could the penalty be avoided if the vehicle was designed to weigh in at say, 1,995 grams, and the last bits of sand were added while the vehicle was on the scale, so as not to go over and get the construction violation?

Thanks!

[windu34]

Question about the scoring rule 6d. Our team has a hovercraft that works at 2 kg. To ensure full credit for the MS, there's a small container of sand ballast - the strategy is to adjust that mass at impound, to make sure the vehicle registers 2,000.0 grams on the supervisor's scale. Rule 5g leaves the possibility open that this mass check will be done right before a run. Re-reading the rule, I'm worried that they'd have 2,001 grams, have to remove a gram of sand before the run, and get the 0.7x penalty.

So to summarize, 1) has anyone used this strategy successfully, and if so, was the measurement during a pre-competition impound, or right before the run?
2) could the penalty be avoided if the vehicle was designed to weigh in at say, 1,995 grams, and the last bits of sand were added while the vehicle was on the scale, so as not to go over and get the construction violation?

Thanks!

Mass of hovercraft is supposed to be weighed at impound I believe. When a craft doesn't meet spec, teams have until the end of impound period to get it in spec. This includes mass

[dcrxcode]

I am looking at computer fans right now and I found one that has a high CFM. However, when I looked at the operating voltage in the datasheet, the voltage range is from 10.8 to 12.6. I was wondering if this fan will still run or not. Will the fan still be powerful? I already ordered the fan, so if there is a problem, please let me know so I could cancel the order.

This is a problem that happened to our team. We tried to run the fan with a 8.4V NiMH that was a bit overcharged to about 9V, but it still wasn't enough voltage to run the fan. I would recommend cancelling your order and getting a different van with lower voltage requirements. If you ordered from Digi-Key, they're very good about returns and order cancellations in my experience.

Did you find any good fan from Digi-Key? Because Those with high CFMs from Digi-Key, that I found, didn't work with the low voltages that are allowed. Also, how did your team control the speed of the hovercraft, because I am experiencing a problem with using a potentiometer with mines?

If you look in earlier pages on this forum you'll find recommendations for quite a few fans from Digi-Key as well as the method for calculating how much CFM and static pressure (which is more important for ensuring enough hovering power) You'll also find recommendations for potentiometers that have worked for a variety of teams.

[chalker]

Question about the scoring rule 6d. Our team has a hovercraft that works at 2 kg. To ensure full credit for the MS, there's a small container of sand ballast - the strategy is to adjust that mass at impound, to make sure the vehicle registers 2,000.0 grams on the supervisor's scale. Rule 5g leaves the possibility open that this mass check will be done right before a run. Re-reading the rule, I'm worried that they'd have 2,001 grams, have to remove a gram of sand before the run, and get the 0.7x penalty.

So to summarize, 1) has anyone used this strategy successfully, and if so, was the measurement during a pre-competition impound, or right before the run?
2) could the penalty be avoided if the vehicle was designed to weigh in at say, 1,995 grams, and the last bits of sand were added while the vehicle was on the scale, so as not to go over and get the construction violation?

Thanks!

Mass of hovercraft is supposed to be weighed at impound I believe. When a craft doesn't meet spec, teams have until the end of impound period to get it in spec. This includes mass

Event supervisors have a lot of leeway on how to handle this. Some will weigh at impound, some right before a team competes, some right after a successful run, some will use a combination of these. However, I have to concur that you should just play it safe. A device weighing 1995 grams will lose at most 0.0625 points on the mass score to a device at 2000 grams exactly. However, it's unlikely a device would come in at exactly 2000 grams. That's going to be noise compared to variations in the time score.

[LittyWap]

You just have to have the right potentiometer. As far as I know, no potentiometers exist that support such high current LiPo/NiMH batteries. Either pick weaker batteries, add more mass, or use cover sheets or something.


-p

There most definitely are potentiometers available that can handle the current from batteries. Check out this Digikey link and filter by power: https://www.digikey.com/products/en/pot ... ageSize=25

I agree. This 5 Ohm beast -- which looks like it spent a decade in a Kazakhstan warehouse -- worked well for us: https://www.amazon.com/gp/product/B00K8 ... UTF8&psc=1

What are the Coulombs and mAh of your battery? I think we tried that same potentiometer, but we burned it out. I may have to downgrade my batteries to whatever you are using so that it functions. That would be a great help. Thanks a bunch!

[CMS AC]

Our hovercraft can only hold1500g. We have a foam tray with a small motor.
Whoever has a working 2KG hovercraft, can you answer these questions?
1) What is the base made out of? Design+Material.
2) Skirt design?
3) Both motors to push forward and downward
4) Propeller?
5) Batteries?

It would be great if anyone could send us a picture.

Thank you!

[CMS AC]

Our hovercraft can only hold1500g. We have a foam tray with a small motor.
Whoever has a working 2KG hovercraft, can you answer these questions?
1) What is the base made out of? Design+Material.
2) Skirt design?
3) Both motors to push forward and downward
4) Propeller?
5) Batteries?

It would be great if anyone could send us a picture.

Thank you!

Sorry for double posting, but any expenses will not be a problem for us. Any battery/motor will work.

[chalker]

There most definitely are potentiometers available that can handle the current from batteries. Check out this Digikey link and filter by power: https://www.digikey.com/products/en/pot ... ageSize=25

I agree. This 5 Ohm beast -- which looks like it spent a decade in a Kazakhstan warehouse -- worked well for us: https://www.amazon.com/gp/product/B00K8 ... UTF8&psc=1

What are the Coulombs and mAh of your battery? I think we tried that same potentiometer, but we burned it out. I may have to downgrade my batteries to whatever you are using so that it functions. That would be a great help. Thanks a bunch!

Let's do some quick math: That rheostat is rated at 50W. The max voltage allowed is 9V. Using P=V*I, that means it can handle up to 5.5 Amps. A good rule of thumb with battery packs is that you divide the mAh rating by 1000 to get the max current it can discharge. Hence, if you are using a 5000 mAh battery pack like the ones a lot of people have been recommending, it should be discharging at about a 5 Amp max current, which is within the spec of the rheostat. Now if you have multiple of those packs in parallel, each discharging multiple amps simultaneously, you could have issues. However I'm not sure that you truly need that much current for any fans you might use for this event. Regardless, there are rheostats that can handle multiple hundreds of watts if need be.

[chalker]

Our hovercraft can only hold1500g. We have a foam tray with a small motor.
Whoever has a working 2KG hovercraft, can you answer these questions?
1) What is the base made out of? Design+Material.
2) Skirt design?
3) Both motors to push forward and downward
4) Propeller?
5) Batteries?

It would be great if anyone could send us a picture.

Thank you!

Sorry for double posting, but any expenses will not be a problem for us. Any battery/motor will work.

I'd suggest you read carefully through this whole thread. There are lots of good recommendations for specific components you can use.

[azkbisfb]

There most definitely are potentiometers available that can handle the current from batteries. Check out this Digikey link and filter by power: https://www.digikey.com/products/en/pot ... ageSize=25

I agree. This 5 Ohm beast -- which looks like it spent a decade in a Kazakhstan warehouse -- worked well for us: https://www.amazon.com/gp/product/B00K8 ... UTF8&psc=1

What are the Coulombs and mAh of your battery? I think we tried that same potentiometer, but we burned it out. I may have to downgrade my batteries to whatever you are using so that it functions. That would be a great help. Thanks a bunch!

The battery pack for our lateral fan was pretty low capacity-- about 2000 mAh. We had more trouble getting our vehicle to slow down than getting it to go faster (the target for the state finals was 20 seconds at 130 cm, which was very difficult to hit (we couldn't)).