L293D motor use (novice)

[bighed]

Hi everyone,

I am a 2nd year mechanical engineering student from the University of New South Wales (Australia). At this point I have no experience whatsoever with electronics but will need some for the project I have been set.

This project allows at maximum, the use of 4 AA batteries. A device needs to be created which completes a track of about 10-15 metres in under 30 seconds, at some pts it will need to climb an incline of 30 degrees (for about 1 m) or climb over barriers (up to 5cm high). The device must also be able to turn

I recently purchased the AXE023 which comes with the L293D. I'm thinking i will need to use H-bridge's to control two motors but have no experience with transistors/diodes/resistors and which to choose for the task.

I have already looked at some schematics on how h-bridges are wired, but I have no clue on which transistors and diodes (to stop noise) to use.

The device would weigh approximately 1-2kg.

Any help or advice for this project would be greatly appreciated.




Thanks,

John

 

[BeanieBots]

The L293 IS an H-Bridge.
How to wire it is clearly shown in the AXE023 manual.
Raising 2kg up a slope to cover the distance in the time might be a hefty load for it though
Do you have any motors yet?
If yes, what is the spec? How much current will be drawn?
Gearbox?, Wheel size?

You MUST sort out the physics and dynamics BEFORE you design the electronics.

 

[goom]

If you do not need reverse, then an H-bridge is unnecessary (but you could still use one). You could simply drive a motor via a MOSFET fed with pulses (PWM command).
Probably the simplest solution would be to buy a cheap 2-channel hobby RC receiver/transmitter. The receiver throttle output could be fed into the Picaxe (see pulsin command) which could perform the necessary calculations and output to the MOSFET (e.g an IRF530) which would power the drive motor. Don't forget the diode to catch the back EMF from the motor.
The other channel could be used to drive a cheap hobby servo for steering.
Now you have a basic RC car.
I have schematics, code and PCB layouts for both MOSFET and L293 based speed controllers using a Picaxe 08M, but I suppose that you should really do some of the hard work yourself. Here's a basic schematic anyway (assuming that I have figured out how to attach a picture).

 

[moxhamj]

Can you tell us more about the rules? The easiest option is to buy a radio controlled car, rip out the controller and replace them with your own (picaxe controlled, of course!). I did it as a project once in an afternoon as I couldn't bear to throw away a RC car where the output transistors had died. But maybe that is not allowed? In which case, are you allowed to use motors or do you have to build them from scratch? Can you use the pre-built mechatronics that Jaycar sells (motor/gearbox combos)? If so, then you need a platform, motors, gearboxes, a servo for steering and/or dual motor controls. Maybe forward and reverse - either H bridge or a single mosfet with a reversing relay (both options have merit). There is the picaxe robot platform as well. The picaxe manuals have some good circuits - eg how to drive a reversing relay from a picaxe using a transistor/resistor/diode.

Also, it seems in the UK if students get help from a forum like this they need to acknowledge that help. Do any rules like that apply?

Do you have a timeframe and a budget?

Short answer is that picaxe can do all this and lots of people can help you but you may get more marks for doing some/all of it yourself!

 

[hamchapman]

As far as I know, the only advantage of using an L293D over some kind of a MOSFET system is that using the L293D you can reverse and travel forward. But by the sounds of it, reverse is unnecessary for you. So I'd probably ignore the L293D...unless of course it's compulsory.