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Old Nov 23, 2011, 01:47 AM
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Joined Nov 2011
2 Posts
Help!
I need help with the electronics of my RC project!

Hello, I am new both here, and to the more advanced parts of RC, or rather the beginners stuff of RC, i dont know anything about anything related to transmitters and receivers.

Right now i am constructing a remote control tank though not a tank.
It will be more like a mars rover if anything.

Anyway, heres what ive got so far, though i recon almost everything will need to go.
I have 4 relays which drive two massive 18kRPM 12vdc brushed motors on either side of the tank, these relays are operated by a cheap rc receiver i scrounged from a $20 toy car. Though remarkably works at 100-300M .
thats it. its just a board with two motors and a bunch of relays.
It cant go backwards without a separate power supply for reverse, but i will solve that with a DPDT relay the power supply im using is 30x AA NIMH batteries (1.2v@3A), which are balance charged and combined into one big 12V 9AH battery.

My problem i have ATM is that i need an ESC for the tank since on/off wont cut it, well actually i need two ESC's , as each side of the tank is to be driven by either motor.
This brings on further problems. i have no idea in how to build any of the things neccesary to remotely run the motors with an esc, and i dont know what i should be looking for in buying the neccesary bits.

Ive looked around, but until recently i havent made any breakthroughs in understanding rc speed controlling.

On hobbyking.com ive seen some receiver remote transmitter pairs which look good, and have about 6-8 chanels which also looks pretty good.

I need to know though what ill need to get and do to said things, in order to drive my two motors with esc's, but still having other channels free to do other things with if possible.
heres what im looking at right now
http://www.hobbyking.com/hobbyking/s...de%5F1%5F.html
It says it can be modified with a computer, which im hoping will allow me to set everything up as i want, but honestly i dont know anything about how it all works. otherwise does anyone know of any others that would suit me better?
The receivers seem to have multiple pins for multiple channels, i would imagine the motors only taking up 2 channels, 4 at most, but that leaves unused channels which i would like to use for other things if i can, which cant work with on off signals like a camera pivot, which i will cover with my long range 433mhz transmitters and receivers.

I currently dont trust my current knowledge of RC modules enough to want to buy this, plus it doesnt say how far it will work at.


Heres what i want my tank to do
  • Run either motor at variable speeds with the corresponding side of the remote
  • Operate a pivot with a stepper motor
  • Work at over 300m, though ive seen pairs which operate over 1.25km which i would preffer if anyone knows of them
  • A stepper control for shifting gears (maybe, depending on how weak the motors are when moving slowly)

Please help me, i really want to learn about RC as much as i want to build my project. thanks-
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Old Nov 24, 2011, 07:29 PM
mostly newbie
shimniok's Avatar
United States, CO, Centennial
Joined May 2011
263 Posts
I suggest starting with the motors and speed control. To understand how a hobby RC ESC works, first understand how a servo works. When RC cars used gas motors, a servo was used to move the throttle and when electrics came out the same servo signal -- without the servo and gas motor -- was used to control them.

You can Google servo pulse train or servo pulses or stuff like that. The summary is, servos expect a pulsetrain with a 20ms period (50hz) with a positive pulse that lasts between 1ms and 2ms. When the servo receives 1ms pulses, the servo goes all the way in one direction. When it receives 2ms pulses it goes all the way in the other direction. 1.5ms is center, and any other pulse width results in a proportional servo arm position.

Likewise, ESC's also expect a servo pulsetrain and, for example, 2ms is full throttle forward, 1ms is full reverse, and 1.5ms is stop and everything in between provides proportional throttle control.

So if all you're doing is remotely controlling something, it's best to learn about remote control parts and pieces in the dedicated RC parts of the forum versus the robotics part. In short you just need an appropriate ESC that can handle the voltage and current of the motors, a receiver (RX), transmitter (TX) with enough channels to drive everything, and otherwise you're good to go I think.

30 AAs?! That sounds inconvenient. What about about NiMH *packs* in a larger cell size like Sub C ? Or if you are willing to carefully learn about safety and handling first, a LiPo pack as they will be able to deliver more current and are lighter and smaller.

How big is this vehicle?

Your motors will take up 1ch per motor.

You don't need to operate a pivot with a stepper; just use a Servo and that simplifies the design considerably. Just plug it into the receiver. Likewise, a big enough servo can shift gears, although you may not need gears. DC motors have a wide operating rpm range.
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Old Nov 24, 2011, 09:34 PM
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Joined Nov 2011
2 Posts
hang on!
Your saying all i need to do is send my signal at 50hz!
As in transmit 433mhz for example, on and off at 50hz!thats super easy! all i would need is a pentiometer , and 555 timer on my transmitter.

I cant beleive how simple this is i wonder why such complex systems are normally used to do this when its so simple, whatsmore why a stepper motor would need 4 channels.
This completely changes everythng!
It can be done with 433mhz right? or should i go with 2.4ghz?
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Old Mar 07, 2012, 06:00 PM
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Joined Jan 2012
186 Posts
i say 2.4ghz
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Old Mar 12, 2012, 01:01 AM
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Port Huron, MI
Joined Dec 2009
1 Posts
To control the ESC's a look into a V-Tail mixer. I may be what you need to control the drive direction smoothly from one stick (2 channels) with limited programming on the transmitter side. that would leave the second stick for an arm or pan tilt head. and the other knob or toggle switches for what ever. something like http://www.hobbyking.com/hobbyking/s...idProduct=6321 . hope it gives you some ideas.
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