Hovercraft B/C

[55555]

a small digital volt meter (also affordable)

Wouldn't a volt meter attached to the wires be illegal b/c it uses an integrated circuit?

[HandsFreeCookieDunk]

a small digital volt meter (also affordable)

Wouldn't a volt meter attached to the wires be illegal b/c it uses an integrated circuit?

I believe the volt meter is just for testing purposes. You just need it to know how much voltage is going into your motor, so you can take it off before you actually do the runs.

[Sean_Sylvester1]

One approach is for a plain DC motor(no brushless), A shaft adapter for propellers and a prop of choice that is a legal size. Add to this a potentiometer of appropriate capability (and affordable) and a small digital volt meter (also affordable).
The motor is a 12 volt motor as 9 volt ones are not plentiful with about a 5,000 rated RPM. You determine the voltage required for the fastest run and then the slowest run. You may have to trim the ends of the prop off a bit and start over.
If your hovercraft is repeatable, you can find the voltage for each time and or distance. Some interpolation may be required if you can not test for all possibilities. This will allow you to nail a good score.

Avoid using pots, when attached to a LiPo or NiCad the heat loss is NOT negligible. PWM is a much better option

[retired1]

As far as the voltmeter, My knowledge goes back to analog.So, I pulled up a digital schematic and it did have 2 IC's. Therefore it can not be hardwired in.
PWM- I know virtually nothing about that for brushed motors. I am assuming that the push motor should be brushed. Have not looked at the rule change that close. I have lots of brushed motors, so will stay with that for the push fan. Will have to look at the energy draw to heat in the pot. Got one that is a bit oversized to make sure that it could stand the load. Along with that, it should only be on for 60 seconds or less.(till we learn more).
It is not a regional event for us, so it will be a while before we worry about that.

[RJohnson]

One approach is for a plain DC motor(no brushless), A shaft adapter for propellers and a prop of choice that is a legal size. Add to this a potentiometer of appropriate capability (and affordable) and a small digital volt meter (also affordable).
The motor is a 12 volt motor as 9 volt ones are not plentiful with about a 5,000 rated RPM. You determine the voltage required for the fastest run and then the slowest run. You may have to trim the ends of the prop off a bit and start over.
If your hovercraft is repeatable, you can find the voltage for each time and or distance. Some interpolation may be required if you can not test for all possibilities. This will allow you to nail a good score.

Avoid using pots, when attached to a LiPo or NiCad the heat loss is NOT negligible. PWM is a much better option

I would strongly recommend against PWM (pulse width modulation) as ICs are illegal in this event, and PWM signals are digital pulses precisely timed by an internal clock (IC) and received by an IC to interpret the signal.

Potentiometers aren't the only way to achieve the goal, but PWM control uses Integrated Circuits and is therefore against the rules...

Good luck!

[HandsFreeCookieDunk]

I did an estimate by scaling down larger hovercraft propellers and found that you'll need about 50 CFM to go full speed with a 2kg craft. Does this sound reasonable?

[windu34]

I did an estimate by scaling down larger hovercraft propellers and found that you'll need about 50 CFM to go full speed with a 2kg craft. Does this sound reasonable?

Very reasonable, but keep in mind our hovercrafts will not be very comparable and youll likely need much more CFM. There is a fan on amazon with 200 CFM for a reasonable price.
I attached a grate/mesh over the propulsion fan that I laser-cut out of acrylic. Reduces thrust by ALOT. Might have to look for a different solution.
What have you guys tried as far as materials for the grate?

[HandsFreeCookieDunk]

I did an estimate by scaling down larger hovercraft propellers and found that you'll need about 50 CFM to go full speed with a 2kg craft. Does this sound reasonable?

Very reasonable, but keep in mind our hovercrafts will not be very comparable and youll likely need much more CFM. There is a fan on amazon with 200 CFM for a reasonable price.
I attached a grate/mesh over the propulsion fan that I laser-cut out of acrylic. Reduces thrust by ALOT. Might have to look for a different solution.
What have you guys tried as far as materials for the grate?

I happened to have some chicken wire that's fine enough to meet the guidelines, so that's what we're going with. My concern with buying the most powerful fan on the market is that if it's too powerful, it might be difficult to precisely control its output at the lower speeds. Since, as a percentage of the fan's total power, the difference in power between two speeds would be less, I feel like it would be easier to control if you get a propeller that maxes out near the top speed.

[seadog]

I have a quick question. Where can I get the wire mesh material for my hovercraft? I cannot find anything suitable in any store and I am not sure where to buy this online either. Any help would be appreciated. Thanks!!

[chalker]

I have a quick question. Where can I get the wire mesh material for my hovercraft? I cannot find anything suitable in any store and I am not sure where to buy this online either. Any help would be appreciated. Thanks!!

Try Home Depot or Lowes.