RC Car

[shinds]

I have been tasked with producing a remote control for project for my apprenticeship. It needs to move forwards and backwards and turn left and right, remotely. simple enough?

looking at using a picaxe setup but i am completely new to this.

i understand all the different outputs and the use of the binary code.

but I am stuck on the input data. How will my receiver talk to the microcontroller, is it capabably of transforming the rf signal into a a usable output? How? are there any additional componants i will need?

Any advice will be appreciated.

Thanks

 

[BeanieBots]

Welcome to the forum.

How will my receiver talk to the microcontroller, is it capabably of transforming the rf signal into a a usable output? How? are there any additional componants i will need?

Might be a good idea to tell us what you have in the way of radio transmitter and receiver. Then we can advise on how to connect it up.

What type of motors do you have? What current do they draw?
We need to know that to advise on what type of motor driver to use.

 

[boriz]

Remote control does not necessarily mean RF. In fact a Picaxe can easily receive IR data from a TV remote style IR transmitter. It would simplify things a great deal. Find the INFRAIN command in the manual.

 

[shinds]

i havent bought any items yet, still at the planning stage.

will i be able to control the speed with IR aswell?

 

[BeanieBots]

You could use IR to control speed but the response might be a little slow.
IR control would need to send a 'command', so you could either send a specific speed or an instruction to increase speed.
The former would require a 'button' for each speed, for the latter, you would need to decide by how much the speed is to increase by for each button press.

Not sure if there would be "interaction" between PWMout (required for speed control) and receiving IR signals. Never tried it.

 

[hippy]

You could control speed using IR, one button could increase speed, another decrease it, and there are other options.

There are many possibilities, but what you need and how best to go about it depends on what you want, and only you can decide that. The first thing you need to do as part of your planning and preliminary investigations is to decide what you'd like your project to be and how you'd like it to be done.

For example, are you looking to use an off-the-shelf Radio Control system with 'sticks' for direction and speed or something else ?

The better the description of what you'd like, and the more precise the questions, the better, more useful, and more specific answers are likely to be. Like choosing to buy a car, there are so many options that you need to narrow down what you want and what's important and not or you may end up overwhelmed by helpful suggestions but no further forward.

 

[shinds]

I have been doing some research

I already have a futaba controller and receiver (from an old remote control car) so i am going to use these. Then have the analogue signal changed to pwm by the microcontroller to controll the speed and direction for the motor. setting limits from readings of an oscilliscope. using a similar method again for a servo for turning.

does this make sense and is it feasable?

 

[BeanieBots]

have the analogue signal changed to pwm by the microcontroller to controll the speed and direction for the motor

What analogue signal? Where?
The Futaba Rx unit will be putting out PWM servo pulses every 20mS, no analogue signals.

 

[shinds]

What analogue signal? Where?
The Futaba Rx unit will be putting out PWM servo pulses every 20mS, no analogue signals.

thats even better then, cool.

will the microcontroller be able to handle driving the motor and the servo at the same time or would i need two chips? one for each signal?

 

[BeanieBots]

Have a read of manual 2 appendix 2.
You may well be better off splitting servo and motor drive between two PICAXE chips but there way around most conflicts. For example, servo outputs can be generated using pulsout and generating the frame rate within your code.
However, it is not clear what part the PICAXE needs to play.
The Rx unit will drive a servo directly, that it what it was designed to do.
Readily available ESC units will take the Rx output and drive motors.

What do you want the PICAXE to do?
I don't want to put you off using a PICAXE but it's not clear why you need one.
Do you want to design your own ESC? (electronic speed controller)
Do you want your 'car' to use tank steer or conventional steer?

You need to spec out what your requirements for the 'car' is before you can start solving any problems relating to those requirements.

If you already have 'standard' radio gear and a 'standard' car, then your best bet is to use 'standard' off the shelf RC speed controllers and servos.

If you want convert 'standard' steering servo signals into tank steer motor control commands (or vice versa) then a PICAXE would be a good choice.

At the moment, it's all too vague to give any good advice.

 

[shinds]

More research more work done.

I have to make my own ESC its is part of my assignment.

I am going to be using conventional steering so this will be controlled straight from the Futaba FP-R122JE Receiver to a Futaba S3003 servo.

The picaxe setup is the Picaxe Stater Pack 18X1 (AXE002U) with a Darling Driver.

to drive the car i will be using a 6v 540 motor possibly this one http://www.mfacomodrills.com/motors/540.html using a 4.8V NiCD Supply.

this motor uses about 7A current though and the Darlington Driver only outputs a recommended max of 400mA

Am i missing something here, is am i trying to do something impossible?

 

[BeanieBots]

No, you're not missing something.
The darlington is good for about 400mA and your motor needs about 7A.

Actually, you really need to cater for around 10A with a 540 motor.

So, you need to make a choice.
Either use a different motor or consider learning about FET transistors.
Personally, given your level of experience, I would strongly suggest against any attempt at building a 10A ESC for use at 4.8v.
You will need to 'bank' together several FETs and use special driving techniques. You will also require some good equipment such as a DSO.

The darlington outputs can be paralleled to give higher currents so a 1A motor should not be too hard to drive.
However, note that a darlington transistor loses about 1.2v.
If your supply is 4.8v, that only leaves around 3.6v which needs to be taken into account. Also, it can only SINK current, so if you want to reverse the motor, you will need a relay. It cannot be done with the darlington array alone.

Have think and get back when you know which way you want to go.

 

[Wrenow]

WARNING: You need to look at the worst case, the stall amp draw. For the 540, depending on the exact model, that is anywhere from 32A to 70A. http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=rs_540rhsh

Can you use a premade ESC and just control it from the Picaxe?

Building a 70A reversible ESC can be done, of course, but it is not exactly trivial (well, at least not to me at my current skill level - might be to others).

Cheers,

Wreno