Hovercraft B/C

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antoine_ego
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Re: Hovercraft B/C

Postby antoine_ego » February 6th, 2017, 11:49 am

Does anyone know if a rotary dimmer would work to vary the speed of the push fan? We will be using two 7.2v NiCd RC racing batteries, one for the lift fan and one for the push fan.

Push fan - http://www.digikey.com/product-detail/e ... ND/5209819
Rotary dimmer in question - https://www.lowes.com/pd/Lutron-Rotary- ... er/1059607

Thoughts?
Since rotary dimmers are basically variable resistors, assuming you can connect them, you should be able to use them. Since you are running 7.2V batteries, and these dimmers are meant for maximum 120V, I would think they would work.
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Re: Hovercraft B/C

Postby 0ddrenaline » February 6th, 2017, 2:21 pm

Does anyone know if a rotary dimmer would work to vary the speed of the push fan? We will be using two 7.2v NiCd RC racing batteries, one for the lift fan and one for the push fan.

Push fan - http://www.digikey.com/product-detail/e ... ND/5209819
Rotary dimmer in question - https://www.lowes.com/pd/Lutron-Rotary- ... er/1059607

Thoughts?
I believe that we considered a dimmer but it had an integrated circuit. I think the dimmer in that link will work if it doesn't have an integrated circuit.

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Re: Hovercraft B/C

Postby andrewwski » February 6th, 2017, 10:14 pm

Does anyone know if a rotary dimmer would work to vary the speed of the push fan? We will be using two 7.2v NiCd RC racing batteries, one for the lift fan and one for the push fan.

Push fan - http://www.digikey.com/product-detail/e ... ND/5209819
Rotary dimmer in question - https://www.lowes.com/pd/Lutron-Rotary- ... er/1059607

Thoughts?
Since rotary dimmers are basically variable resistors, assuming you can connect them, you should be able to use them. Since you are running 7.2V batteries, and these dimmers are meant for maximum 120V, I would think they would work.
Dimmers are typically *not* variable resistors (rheostats/potentiometers). If they were, they'd have to dissipate a LOT of heat when the light was dimmed, and would get very hot.

Dimmer switches are used in AC, and they essentially "chop" the sine wave. When the polarity switches direction (crosses zero), it cuts the power supply until the wave reaches a certain voltage, at which point it allows it back through. This voltage is what you're controlling through the dimmer.

Most dimmers contain integrated circuits, which are not allowed in this event. But they won't work on DC anyway.

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Re: Hovercraft B/C

Postby keastman » February 7th, 2017, 8:02 am

In regards to "vehicles must have an electric switch to permit safe starting"... If you are using two motors can they each be turned on with a separate switch or do they have to be linked to a single switch to turn it on?

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Re: Hovercraft B/C

Postby HandsFreeCookieDunk » February 7th, 2017, 9:02 am

In regards to "vehicles must have an electric switch to permit safe starting"... If you are using two motors can they each be turned on with a separate switch or do they have to be linked to a single switch to turn it on?
Disclaimer: This is one man's opinion and is in no way an official rules clarification.

I can't imagine that would be a problem. As long as you are safely starting all your fans, I don't see why a supervisor would care what order you do it in.

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Re: Hovercraft B/C

Postby kenniky » February 7th, 2017, 9:22 am

In regards to "vehicles must have an electric switch to permit safe starting"... If you are using two motors can they each be turned on with a separate switch or do they have to be linked to a single switch to turn it on?
Ours had multiple switches. It should be fine.
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Re: Hovercraft B/C

Postby NyeSpy » February 7th, 2017, 12:05 pm

I have had multiple electronics "gurus" suggest using a discrete transistor circuit to control the push fan speed. I am being told that this would not be the same as an integrated circuit. Before I invest a ton of time learning about discrete transistor circuits, are they allowed for this event?

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Re: Hovercraft B/C

Postby chalker » February 7th, 2017, 3:40 pm

I have had multiple electronics "gurus" suggest using a discrete transistor circuit to control the push fan speed. I am being told that this would not be the same as an integrated circuit. Before I invest a ton of time learning about discrete transistor circuits, are they allowed for this event?
As usual, this is not the place for official statements. SOINC is where you should go for that. Unofficially though:

We’ve had this situation come up in previous years / other events as well. Technically this is correct, in that a single transistor does NOT meet the definition of an integrated circuit. Last year I personally saw an amazing Mission Possible device where the kid had essentially constructed an ASIC out of LOTS of individual transistors to get around the no ICs rule. The issue is that while I closely inspected it, I didn’t have the time, nor the ability wihout deconstructing it to verify each and every component was only a transistor and he hadn’t snuck a true IC into it.

Hence, I would point out that most event supervisors won’t have the knowledge / ability to verify that a given small black box is a single transistor vs. an integrated circuit (for example, some voltage regulators look EXACTLY like a transistor but clearly are an IC). You will be at risk to having your device DQ’d if you bring something with lots of transistors that can’t be verified in a timely manner by an unskilled supervisor.

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Re: Hovercraft B/C

Postby RJohnson » February 8th, 2017, 2:45 pm

I have had multiple electronics "gurus" suggest using a discrete transistor circuit to control the push fan speed. I am being told that this would not be the same as an integrated circuit. Before I invest a ton of time learning about discrete transistor circuits, are they allowed for this event?
As usual, this is not the place for official statements. SOINC is where you should go for that. Unofficially though:

We’ve had this situation come up in previous years / other events as well. Technically this is correct, in that a single transistor does NOT meet the definition of an integrated circuit. Last year I personally saw an amazing Mission Possible device where the kid had essentially constructed an ASIC out of LOTS of individual transistors to get around the no ICs rule. The issue is that while I closely inspected it, I didn’t have the time, nor the ability wihout deconstructing it to verify each and every component was only a transistor and he hadn’t snuck a true IC into it.

Hence, I would point out that most event supervisors won’t have the knowledge / ability to verify that a given small black box is a single transistor vs. an integrated circuit (for example, some voltage regulators look EXACTLY like a transistor but clearly are an IC). You will be at risk to having your device DQ’d if you bring something with lots of transistors that can’t be verified in a timely manner by an unskilled supervisor.
I've used discrete transistors in no IC events before, and I've had two types of ES's: 1. Those that just take my word for it. 2. Those who are cool with it after I show them the technical specifications. Buy a product with a number on it so the specs sheet matches and that verifies it for them.

Good luck!

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Re: Hovercraft B/C

Postby windu34 » February 9th, 2017, 8:01 am

I have had multiple electronics "gurus" suggest using a discrete transistor circuit to control the push fan speed. I am being told that this would not be the same as an integrated circuit. Before I invest a ton of time learning about discrete transistor circuits, are they allowed for this event?
What is the advantage of using a switching circuit made up of transistors to control speed over regulating current to the motor with a variable resistor?
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Re: Hovercraft B/C

Postby DannyK » February 9th, 2017, 9:45 am

I am a volunteer parent since our school's science teacher will not coach. I am in health care by training, so no knowledge of any use.
I have read every post in this chain and obtained the following items that seemed to be reasonable based on my reading.
http://www.digikey.com/product-detail/e ... -ND/203771
http://www.digikey.com/scripts/DkSearch ... 6580673197
I have a 7.2 volt, 3000mAH NIMH battery from VEX that we used during BEST robotics.
I took all the items into my local RC Hobby Store to ask about connectors to hook everything up without causing a fire.
The gentleman in charge of the area said I had multiple problems.
1 The blower would never be able to lift itself much less a 2 kg craft.
2 Hooking the motor to the battery would destroy the battery
3 The motor would probably not turn due to it being 12 v and the battery being 7.2.
4 The blower needed an IC controller to function, he tried to hook the blower up to a LiPO battery and said that was the reason it would not work for him.
5 THe blower needed 3 wires to function safely. It came with 2 but has a connector for a third.
I nodded and told him I must have misunderstood what I had read.
If someone can provide some sort of guidance, I would appreciate it.
Has anyone actually used these items successfully?
I do not want to start a fire, cause an explosion or turn my team members away from wanting to do this type of activity but fear I am going to disappoint them.
We did order the Ward Kit several weeks ago but it has not shipped.
Thank you

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Re: Hovercraft B/C

Postby antoine_ego » February 9th, 2017, 4:22 pm

I am a volunteer parent since our school's science teacher will not coach. I am in health care by training, so no knowledge of any use.
I have read every post in this chain and obtained the following items that seemed to be reasonable based on my reading.
http://www.digikey.com/product-detail/e ... -ND/203771
http://www.digikey.com/scripts/DkSearch ... 6580673197
I have a 7.2 volt, 3000mAH NIMH battery from VEX that we used during BEST robotics.
I took all the items into my local RC Hobby Store to ask about connectors to hook everything up without causing a fire.
The gentleman in charge of the area said I had multiple problems.
1 The blower would never be able to lift itself much less a 2 kg craft.
2 Hooking the motor to the battery would destroy the battery
3 The motor would probably not turn due to it being 12 v and the battery being 7.2.
4 The blower needed an IC controller to function, he tried to hook the blower up to a LiPO battery and said that was the reason it would not work for him.
5 THe blower needed 3 wires to function safely. It came with 2 but has a connector for a third.
I nodded and told him I must have misunderstood what I had read.
If someone can provide some sort of guidance, I would appreciate it.
Has anyone actually used these items successfully?
I do not want to start a fire, cause an explosion or turn my team members away from wanting to do this type of activity but fear I am going to disappoint them.
We did order the Ward Kit several weeks ago but it has not shipped.
Thank you
Could you provide a link to the motor in question? I've been using computer fans and have been able to lift a 2kg craft. It is most certainly possible with a good skirt design, provided you have a fan that can supply enough power. You're using a 7.2V NiMH, so that's a little underpowered, but the minimum voltage for most fans is 5V. I would recommend an 8.4V NiMH, that extra volt is really helpful. I'm a little confused as to why the blower needed 3 wires. I've been using 2 and it works perfectly.

As for destroying the battery, I'm quite surprised he said that. Most RC cars have huge current draws, well exceeding 10 amps, so that is probably not the issue. If you could provide more details as to what he said the problem was for the battery that would be great. I'm using an 8.4V NiMH battery designed for RC trucks and it works perfectly. NiMHs are tough. I occasionally need to run it down to 7V to fix the build up of internal resistance, but besides that it's great. I would make sure to have a 'smart' charger that will cutoff when capacity is reached.
Rest in Peace Len Joeris
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Re: Hovercraft B/C

Postby DannyK » February 9th, 2017, 4:40 pm

I am a volunteer parent since our school's science teacher will not coach. I am in health care by training, so no knowledge of any use.
I have read every post in this chain and obtained the following items that seemed to be reasonable based on my reading.
http://www.digikey.com/product-detail/e ... -ND/203771
http://www.digikey.com/scripts/DkSearch ... 6580673197
I have a 7.2 volt, 3000mAH NIMH battery from VEX that we used during BEST robotics.
I took all the items into my local RC Hobby Store to ask about connectors to hook everything up without causing a fire.
The gentleman in charge of the area said I had multiple problems.
1 The blower would never be able to lift itself much less a 2 kg craft.
2 Hooking the motor to the battery would destroy the battery
3 The motor would probably not turn due to it being 12 v and the battery being 7.2.
4 The blower needed an IC controller to function, he tried to hook the blower up to a LiPO battery and said that was the reason it would not work for him.
5 THe blower needed 3 wires to function safely. It came with 2 but has a connector for a third.
I nodded and told him I must have misunderstood what I had read.
If someone can provide some sort of guidance, I would appreciate it.
Has anyone actually used these items successfully?
I do not want to start a fire, cause an explosion or turn my team members away from wanting to do this type of activity but fear I am going to disappoint them.
We did order the Ward Kit several weeks ago but it has not shipped.
Thank you
Could you provide a link to the motor in question? I've been using computer fans and have been able to lift a 2kg craft. It is most certainly possible with a good skirt design, provided you have a fan that can supply enough power. You're using a 7.2V NiMH, so that's a little underpowered, but the minimum voltage for most fans is 5V. I would recommend an 8.4V NiMH, that extra volt is really helpful. I'm a little confused as to why the blower needed 3 wires. I've been using 2 and it works perfectly.

As for destroying the battery, I'm quite surprised he said that. Most RC cars have huge current draws, well exceeding 10 amps, so that is probably not the issue. If you could provide more details as to what he said the problem was for the battery that would be great. I'm using an 8.4V NiMH battery designed for RC trucks and it works perfectly. NiMHs are tough. I occasionally need to run it down to 7V to fix the build up of internal resistance, but besides that it's great. I would make sure to have a 'smart' charger that will cutoff when capacity is reached.
This is the motor/blower.
http://www.digikey.com/scripts/DkSearch ... 6580673197
He seemed concerned that the battery would explode but he lost me as to why.
Thank you

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Re: Hovercraft B/C

Postby antoine_ego » February 9th, 2017, 5:39 pm


This is the motor/blower.
http://www.digikey.com/scripts/DkSearch ... 6580673197
He seemed concerned that the battery would explode but he lost me as to why.
Thank you
Sorry, the link doesn't seem to be working for me, it just sends me to what amounts to the entire DigiKey catalog. He said the battery would explode? The only reason I can think of for a battery exploding is that someone is charging them after they've gone over capacity, or someone charging them at 4C. Don't take my word for it though. As that seemed like the most dangerous concern he had, if you could ask him why he thought that, it would help. It should be noted though, that if a NiMH were to explode, there would be steel shrapnel flying everywhere.
Rest in Peace Len Joeris
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Re: Hovercraft B/C

Postby Ashernoel » February 9th, 2017, 9:00 pm

Hey I have had trouble getting my hovercraft to lift with a large brushed motor and 6 inch propeller (massive ik) and was wondering if getting a blower fan like the one mentioned a lot in the forum, http://www.digikey.com/product-detail/e ... ND/2560506, would be better to generate enough pressure for lift. Would a normal fan, like a CPU fan my computer, with super high CFM then be good to power the thrust to push the hovercraft at 2 kg, or is there some massive math piece I'm missing? Thanks :D
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