boe/rc car

Korrosiv

Hi folks,

Signed up a few days ago but didn't want to post until i had finished with the boe bot builds (self help first!)

I'm after some advice as to the best h bridge (ic or otherwise) for getting the BOE onto an rc car. The rc car has a 6v battery pack, however i intend to 'proof of concept' with it and then look to ramp it up to a bigger car and add on gps etc, so the h bridge will either need to be cheap enough to build a few times or may need to handle up to 12v depending on the beast i put together later. I'm happy enough to try and build a discrete h bridge for the knowledge gain, but likewise an ic would be ok too.

Some idea of the best places to buy the components in the UK would also be much appreciated as I can't seem to find a lot of places to pick up the likes of the LMD18200 chip?

I have a bit of rc building experience and I'm a software developer by profession, but i'm just getting up to speed with the electrical and mechanical side of things so simple explanations would be appreciated


Another concern is that the rc car i want to start with (hobbyzone mini mauler) has a four wire servo for the steering and I'm not sure what bearing that has on the setup i will need? I read that 3 wire servos are the norm and saw some confused looking posts elswhere as to the conversion of 4 to 3 wire. Is it best to change out the servo for something more standard or is it easy enough to convert it to work from the BOE?


Apologies for the number of questions (may aswell ask them all in one thread!), but how complex would it be (bearing in mind a i'm an electrical noob) to interface the boe with the rc electronics that are in the car now? By that i mean i would like to be able to go autonomus and still be able to override with the rc controller should it look like it's going to take out a kid in the park? It may well be a little beyond my current skills but if you dont ask....

Any help would be much appreciated

Sticky

You could start by looking into an LM298. they are easy to use, I got it going, and have two channels so you can use it for two motors. They are pretty robust but I haven't used them above 9.6 volts but I believe they are good for up to 24 volts. I used a separate power supply for the motors and microcontroller, worked better for me. I wired the enable pins together attached them directly to a 5 volt power source through a resistor to save using an output pin to enable them. Hope it helped, if you need further details ask me as I'm not at home atm.

Korrosiv

Thanks for the quick reply sticky. I'll have a look at the LM298 and see where I can source one from.


As for the servo issues, anyone got any ideas? I'd happily change out the servo but I have a feeling the 4 wire could be converted for my uses.

Also looking for any rc experts to chime in on the possibility of interfacing with the rc cars circuitry as is to provide rc and autonomy

Help is appreciated

W9GFO

If you didn't want to build your own controller you could use one of the many RC ESCs out there. OR, you could use a controller like the one I have in my antweight robot. It is a dual 5 amp H bridge plus another one way motor controller to be used for a weapon. It cost less than $50 several years ago. I can not remember what it is called - sorry. There is also the Parallax HB25.

This is what I would do. Get a good speed controller, with reverse (like the HB25) and replace the steering servo with a standard 3 wire. When you move up to a larger car you can re-use the speed controller. You would be up and running right away if you go that route.

As far as interfacing with the car's circuitry, I think that would be more hassle than it is worth. That all-in-one unit may not have a place that outputs standard RC pulse widths that you could tap into.

You could probably do something simple using the RC electronics like sense the voltage on the motor line. Hook up the positive motor wire to a pin on the stamp - using appropriate components to protect the pin, in the main loop check to see that it is high in order to keep moving.

I'm not discouraging building your own H bridge - it is something that I plan to try soon too.

Rich H

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The Servo Boss, a 12 channel servo tester kit from Gadget Gangster.

P!-Ro

you can also use the h-bridge on the rc car itself. i did that once, wasn't too bad. i just cut away what i didn't need and hooked wires to the circuit to run to my chip.

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PG

Korrosiv

Thanks for the inputs folks

I had considred the hb25 and is still an option.

Pi Guy - When i opened up the car and saw the transistors sitting there the thought did cross my mind that what i needed was already there, problem is that i've no idea what to ditch and what to keep, which will no doubt be a problem!


Forgot to ask, what is the chances of using the esc on the car? i read some posts from 2004 about suggestions made to someone looking for more speed. The car has digital proportional steering with an 'All-in-one ESC/receiver' aswell. I gather the ESC can be controlled by PWM?

Pardon any stupid questions, as i say im just getting up to speed with the elctrical side of things!

Post Edited (Korrosiv) : 9/17/2009 4:16:45 PM GMT

P!-Ro

usually there are two different types of transistors connected with large resistors and a small transistor. just connect it to the stamp and you can control the motors.

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PG