Author Topic: Fans and RC  (Read 9329 times)

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Offline gamefreakTopic starter

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Fans and RC
« on: October 13, 2007, 06:45:00 PM »
In the robotics club at my school my teammates want to build RC hover cars next quarter since we dont have anything else going on, but i have a question about computer fans. Since they and servos both have the positive negative and signal wires, if i plug them into an RC channel will they respond similar to a modified servo?

Also where can i find cheap RC transmitters and receivers, I only need 3 channels so all the small and cheap are welcome.

so far for cheapest i have found 70 $ for both a receiver and transmitter(no tax)

Is there any way to make two fans that use PWM do opposite things on the same channel? ex. I push left on the transmitter and the fan on the right speeds up, and the fan on the left slows down.
« Last Edit: October 19, 2007, 04:14:43 PM by gamefreak »
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Offline airman00

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Re: Computer Fans and RC
« Reply #1 on: October 13, 2007, 07:36:59 PM »
They would function sort of like servos except they wouldn't need analog. Then i guess you would need to use a microcontroller to do A2D from a servo receiver and then connect a pin from the microcontroller to the fan. Then you would need to do a relay or H bridge to switch the motors. ( remember motors need backwards polarity to turn backwards while servos just need a different pulse)

Why not just use the 3 channel r/c transmitter from a toy ( the you wouldn't need the whole servo to regular motor thing...). Get it from a toy tank or something that has a turning turret , etc.

Umm, why three channels, all the R/C hovercrafts I've seen have only 2 channels.
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #2 on: October 13, 2007, 08:03:34 PM »
because all receivers i find are 3 channels, and the third could be for add ons

so just plugging the fan into the receiver wont give variable speed?

Also, wouldn't buying a RC tank and taking it apart be more expensive then buying a receiver/transmitter and some servos?
« Last Edit: October 13, 2007, 08:10:57 PM by gamefreak »
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Offline airman00

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Re: Computer Fans and RC
« Reply #3 on: October 13, 2007, 08:27:59 PM »
Quote
so just plugging the fan into the receiver wont give variable speed?
Nope

Quote
Also, wouldn't buying a RC tank and taking it apart be more expensive then buying a receiver/transmitter and some servos?

Are you using computer fans or modified servos???
Also, tanks with 3 channels can be bought for like 20-30 bucks. But remember ,they use DC motors and not servos.
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #4 on: October 13, 2007, 08:35:57 PM »
computer fans, but you need to steer with either a servo or by alternating between two fans

whats different about rc toys that make it so they can just plug motors into the RC receiver?
I do not think that they have microcontrollers like you said would be needed.
« Last Edit: October 13, 2007, 08:39:31 PM by gamefreak »
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Offline airman00

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Re: Computer Fans and RC
« Reply #5 on: October 13, 2007, 08:48:30 PM »
R/C have receivers for D/C motors and those recievers switch polarity while the servo receivers use analog signal changes.

I'm talking about using the R/C reciever that came with the toy. Also, use the alternating two fans idea, its easier.

IF you decide to use the servo reciever anyway than you'll need to do what I said earlier
Quote
u would need to use a microcontroller to do A2D from a servo receiver and then connect a pin from the microcontroller to the fan. Then you would need to do a relay or H bridge to switch the motors. ( remember motors need backwards polarity to turn backwards while servos just need a different pulse)


yes, they don't have the microcontroller that you need ( but they do have an IC onboard, not the ones that are reprogrammable). Just use a PIC micro, they're free ( from samples) but you'll need to buy a programmer.
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #6 on: October 14, 2007, 08:59:05 AM »
alright so what is the point of the third wire on a computer fan?
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Re: Computer Fans and RC
« Reply #7 on: October 14, 2007, 09:50:06 AM »
The fan has a wire for ground and one for +12V. Third wire is for adjusting speed. The fan is designed to spin in just one direction. The fan that has only 2 wires can work both ways, but the one with 3 wires I am not sure. For a hovercraft it doesn't matter, since the fan has to blow only one way. Use a PWM (5 volts) to varry the speed.
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #8 on: October 14, 2007, 10:55:03 AM »
alright, and while i was mowing the idea of using servos and fans entered my mind again. I remembered that i dont need a microcontroller just some limit switches that are connecting the fans to the battery and when the servo turns and activates the micro switch then it turns on/off the fans.

Also any ideas on a light weight battery?
« Last Edit: October 14, 2007, 11:17:59 AM by gamefreak »
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #9 on: October 14, 2007, 06:47:08 PM »
Hey i just found some PWM fans, wouldnt those be easy to plug into a receiver and work just like a modified servo?

http://www.pctoys.com/840556081067.html
« Last Edit: October 14, 2007, 06:48:01 PM by gamefreak »
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Offline airman00

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Re: Computer Fans and RC
« Reply #10 on: October 14, 2007, 06:58:25 PM »
ye, but you can't make them go backwards like a servo
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #11 on: October 14, 2007, 07:11:40 PM »
edit: read the last paragraph of the first post please
« Last Edit: October 15, 2007, 08:07:34 PM by gamefreak »
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #12 on: October 17, 2007, 10:49:23 AM »
anyone know if this is possible?
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Offline airman00

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Re: Computer Fans and RC
« Reply #13 on: October 17, 2007, 02:35:44 PM »
yep if uou use a microcontroller!

have it read the single pwm signal and transfer it into two separate PWM which you program.

Quite simple actually...
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Offline ed1380

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Re: Computer Fans and RC
« Reply #14 on: October 17, 2007, 04:05:01 PM »
from experiance I can tell you that even powerfull 120mm fans won't have enough pressure to move the hovercraft.

get a hobby motor and propellor from a hobby aircraft place. much better and you could use a toy's transceiver.

only problem I see with that is the hobby motors might suck more amps then the standard toy motors do. in that case a relay or relay/silenoid driver is what you'l need
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #15 on: October 17, 2007, 05:09:15 PM »
so there is no way without a microcontroller to turn one rc PWM into two opposite ones?

using 3 4.8 volt 270 MaH batteries and im using 198 MaH without motors. so 270/198=1.36 * 60 = 81.81 minutes. So I am not to worried about the amps.
« Last Edit: October 17, 2007, 05:22:58 PM by gamefreak »
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Re: Computer Fans and RC
« Reply #16 on: October 17, 2007, 05:23:42 PM »
hmmm, you would still need some kind of IC , maybe one exists for your case.

But I would suggest a mcirocontroller like PIC or  AVR, you can then add your own customizations as well as changing the PWM to perfectly suit your needs.

Micro controllers can be gotten as free samples but the actual programmer hardware will cost you something..
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #17 on: October 17, 2007, 05:29:31 PM »
I'm too lazy to program something, so if I'm going to use DC motors then i will just make some space for servos and micro switches.

Now the biggest concern is to find a motor that is cheap and can give the lift i need for this thing.
Also, should i bother with an H-Bridge? or should i just use a resistor? I planned originally to just connect the motor to a micro switch so that when the servo turns the motor gets full power from the batteries, but that might damage it or the batteries....

since all i need is to keep the motors moving at all times should i bother with any type of protection or braking methods?
« Last Edit: October 17, 2007, 06:30:07 PM by gamefreak »
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Offline ed1380

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Re: Computer Fans and RC
« Reply #18 on: October 18, 2007, 04:34:54 PM »
lift motors will need to be on for it to move, so have them turn on as soon as you turn the hovercraft on. (me thinks at least)

for movement, maybe get a rc tank, cause it will have a remote made for diferntial steering (what hovercrafts use) and use motors that came with it attached to propelers, or beaf it up a bit  (read my previous post for more info on that)


and what are you gonna use for the base?
« Last Edit: October 18, 2007, 04:36:31 PM by ed1380 »
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Offline airman00

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Re: Computer Fans and RC
« Reply #19 on: October 18, 2007, 05:00:33 PM »
Quote
for movement, maybe get a rc tank,


then he might as well buy an r/c hovercraft            :D

but seriously , you don't even need an r/c tank. Get a cheap toy car and connect a regular dc motor to the front steering.

Look for motors from allelectronics.com or electronicsgoldmine.com. They should have some cheap ones

Since the motors are only going one way you do not need an H bridge. However, a fuse or a relay( with capacitor) is never a bad idea
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Offline ed1380

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Re: Computer Fans and RC
« Reply #20 on: October 18, 2007, 05:38:40 PM »
toy cars already have dc motors for steering

reason i said tank, is cause he needs a remote with 2 parallel joysticks
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #21 on: October 18, 2007, 06:47:15 PM »
technically all i need is a one channel remote, i could just hook a servo up to a balsa wood rudder and steer like that
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Offline ed1380

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Re: Computer Fans and RC
« Reply #22 on: October 18, 2007, 07:29:18 PM »
technically all i need is a one channel remote, i could just hook a servo up to a balsa wood rudder and steer like that
like ain airboat?
then yes, but what about reverse?
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Re: Computer Fans and RC
« Reply #23 on: October 18, 2007, 08:09:01 PM »
turn around? lol, if we intend to race them then i have no point for reverse, the moment you have to hit 0 speed then you have already lost.

So right now im looking for some powerful fans. hgordon gave me this link:
http://www.hobby-lobby.com/ductfan.htm

but the motor is 70 dollars and uses 14 amps 11 volts, so i need something a little bit more feasible.
any ideas?
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Offline airman00

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Re: Computer Fans and RC
« Reply #24 on: October 18, 2007, 08:15:53 PM »
how big a hovercraft are we talking about?

( in inches please)
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #25 on: October 18, 2007, 09:03:22 PM »
lol, inches

7.87401 in by 6.29921 in, 49.6 square inches, it might end up smaller but im trying to see the worst case scenario

i've been using metric since thats what all physics is..
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Re: Computer Fans and RC
« Reply #26 on: October 19, 2007, 06:36:24 AM »
Well thats pretty small.

Look for motors that are used for r/c helicopters , check for them in some hobby store

Also, I would recommend using balsa wood or even styrofoam to make it as light as possible. also, try to use as little batteries as possible to minimize weight.
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Offline ed1380

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Re: Computer Fans and RC
« Reply #27 on: October 19, 2007, 01:14:16 PM »
6x8
wow that's small

IIRC bigger surface area= more lift per unit of energy


those fans are expensive. what about one of those special fan blades and motor and make your own duct.

and maybe one of these motors and some prop http://www.rctoys.com/rc-toys-and-parts/HI-ND3766/RC-PARTS-BRUSHLESS-MOTORS-HIMAX.html
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Offline gamefreakTopic starter

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Re: Computer Fans and RC
« Reply #28 on: October 19, 2007, 02:55:56 PM »
what about this motor? http://cgi.ebay.com/Tamiya-RS540-RS-540-Sport-Tuned-Motor-TT-TL-01-53068_W0QQitemZ130164784291QQihZ003QQcategoryZ44022QQcmdZViewItem
the motor you gave is still pretty expensive, and this is a fairly cheap high powered motor.

the only problem is the amps it uses, 50+ amps so 3000/50000 * 60 is only 3.6 minutes

then give it a plastic model airplane prop and take a block of styrofoam and sand out the center to make an extremely small gap?
« Last Edit: October 19, 2007, 03:02:43 PM by gamefreak »
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Offline airman00

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Re: Computer Fans and RC
« Reply #29 on: October 19, 2007, 03:06:15 PM »
There are plenty of other motors out there. Look for helicopter motors! I have a small helicopter motor that runs on 6 AA batteries and it is very small. Look in hobby stores like towerhobbies.com for helicopter parts.
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