HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Apr 16, 2006, 05:07 AM
Registered User
Joined Jan 2005
74 Posts
Discussion
Use servo on RC toy car

Hi there,

I've searched for quite a while on the internet but couldn't find anyhting...
I've been to Bangkok in january and found this small black box that on which you can connect a standard servo to make a cheap RC car turn left and right and making the servo turn to it's centre position...I was dumb enough not to buy the black box...

So basically this is what I'm looking for...make a RC toy car steer using a servo left and right and get it to return to its centre position. Does anyone know how to pull this off?

J.
jevries is offline Find More Posts by jevries
Reply With Quote
Sign up now
to remove ads between posts
Old Apr 16, 2006, 07:18 AM
Registered User
Staffs, UK
Joined Nov 2003
10,249 Posts
I just plug the servo into the receiver and, hey presto, left, right, centre just like magic.

I guess you're talking about different RC cars. Can you be a little clearer about what you're looking for ?

Steve
slipstick is online now Find More Posts by slipstick
Reply With Quote
Old Apr 16, 2006, 08:03 AM
Registered User
Joined Jan 2005
74 Posts
I'm sorry for being not clear enough ...
I have two different types of TOY RC cars...1/32 tincar and a 1/10 Racewin car. I always use cheap China made stuff...because A: it's cheap and B: it's a challenge.
They all work with H-bridges that feature NO propotional driving or steering.

Now, I know they sell these small pcb's (black boxes) where you can plug in a standard 3 wire servo and that is connected to the 2 outputs on the cheap RC pcb....the big advantage is you don't need to use the spring centred steering devices anymore because the servo automatically returns to the centre.
Hopefully someone can help me out here.

J.
jevries is offline Find More Posts by jevries
Reply With Quote
Old Apr 16, 2006, 10:04 AM
Registered User
Florida
Joined Aug 2004
4,057 Posts
That little black box is simply putting out a positive going pulse on the signal wire about 1.5 milliseconds long every 20 milliseconds. As you vary that pulse width .5 millisecond either way the servo moves left or right.
Rodney is offline Find More Posts by Rodney
Reply With Quote
Old Apr 16, 2006, 10:16 AM
Registered User
Joined Jan 2005
74 Posts
Is there anyway to get some electronic components and make it myself?
I have no clue how to get the postive pulse going..they use a PIC or something?
Thanx!!
jevries is offline Find More Posts by jevries
Reply With Quote
Old Apr 16, 2006, 11:14 AM
Registered User
North East England UK
Joined Jan 2003
1,432 Posts
Quote:
Originally Posted by jevries
Is there anyway to get some electronic components and make it myself?
I have no clue how to get the postive pulse going..they use a PIC or something?
Thanx!!
You can make use of a 555 timer chip to generate a pulse with the correct frame rate..you can make the pulse width variable too to make the servo go left or right...but I guess you want to do this via a tranmitter?
Chippie is offline Find More Posts by Chippie
Reply With Quote
Old Apr 16, 2006, 04:23 PM
Registered User
Joined Mar 2006
119 Posts
If you can program a PIC, you could place one between the RC car's steering wiring and the servo. Then it could operate the same as the original non-proportional steering.
bearcreek is offline Find More Posts by bearcreek
Reply With Quote
Old Apr 17, 2006, 09:09 AM
Registered User
Florida
Joined Aug 2004
4,057 Posts
There are quite a few circuits to do that using a 555 timer. Just use a search engine and search for "servo tester" or "pulse width modulator".
Rodney is offline Find More Posts by Rodney
Reply With Quote
Old Apr 17, 2006, 10:30 AM
York Electronics
Gary Warner's Avatar
Dallas Tx USA
Joined Apr 1999
2,505 Posts
Quote:
Originally Posted by jevries
I'm sorry for being not clear enough ...

Now, I know they sell these small pcb's (black boxes) where you can plug in a standard 3 wire servo and that is connected to the 2 outputs on the cheap RC pcb....

J.
So the 'cheap RC pcb' is a cheap RC receiver?

Is this a 'toy' car that uses like... two buttons on a transmitter, one for right and one for left and no buttons pushed for strait (or something to this effect)? I take it that the car's normal 'servo', if you will, is just an actuator (solenoid type) movement with a spring return to center. If so, a PIC or 555 circuit could be used to make the 'cheap 2 output' servo drive compatible with a 3-wire servo. But why? It still will be a 3 point controller. The only advantage I could see, is like you mentioned... you won't need a return spring for center. You could do things like slowing the servo movement, but that's about all I can see as a practical reason to change to a 3-wire servo.

If I'm off in track, you may need to explain your question with more details as to why, as well as what you are trying to do.

Gary
--
Gary Warner is offline Find More Posts by Gary Warner
Reply With Quote
Old Apr 17, 2006, 11:55 AM
Registered User
North East England UK
Joined Jan 2003
1,432 Posts
Quote:
Originally Posted by Gary Warner

If I'm off in track, you may need to explain your question with more details as to why, as well as what you are trying to do.

Gary
--
The starting post does seem a little vague......hence my vague answer...
More info, better response.
Chippie is offline Find More Posts by Chippie
Reply With Quote
Old Apr 18, 2006, 04:57 AM
Registered User
Joined Jan 2005
74 Posts
Hi there, Thanx for all your answers!

Gary, thats exaclty what I'm talking and want to accomplish and I tell you why...
if you take apart those 1/32 Tin cars, the ones I work with right now, you will notice that the steering setup is pretty big...130 motor with big gears. This makes it impossible for me to build a custom 1/24 model kit car having all the features inc. interior using cheap components.
A micro servo would be the solution for the steering....otherwise a small geared motor that can be forced back to centre position using a spring...I tell you, such a small gearmotor with the right specs is not so easy to find. For instance a micro servo will never be forced back to centre position using a spring because it has quite some torque.
For a receiver I use one of those (mod out) stuntcar receivers since they have good range and are small enough to hide inside the 1/24 car.

Please check out my website so you can see what I'm working on:
http://www.jevries.com
Here's picture of one of the cars I worked on this one can only lift the rear and hop the front Radio controlled...another one I'm working on will do it all with driving and steering while keeping the interior.


The 555 IC sounds good to me..is it quite simple to put together? Do I need extra components besides the 555 IC?

Thanks for your help guys!
jevries is offline Find More Posts by jevries
Reply With Quote
Old Apr 18, 2006, 11:32 AM
York Electronics
Gary Warner's Avatar
Dallas Tx USA
Joined Apr 1999
2,505 Posts
The 555 servo circuits are all over the web. They do need some additional parts to generate the RC (resistive/capacitance) time constants. This may prove to have a bit of a drawback though. The RC time constants will drift as the battery voltage runs down and temperature changes. This it the primary reason why many of us with micro-controller skills would prefer to take on this project with a PIC or other micro-controller. The other advantage over a 555 design would be the interfacing with the existing R/C receiver. Getting the 555 to change its output based on the inputs from the receiver adds moderate to significant parts and design considerations. With a PIC, you just pipe in the receiver logic levels and code to make the output this-or-that depending on the inputs.

Gary
--
Gary Warner is offline Find More Posts by Gary Warner
Reply With Quote
Old Apr 19, 2006, 02:57 AM
Registered User
Joined Jan 2005
74 Posts
Thanx Gary for explaining it all to me! I see what your saying it isn't too simple because of the side effects. I was hoping on just hooking the 555 up with a mosfet or something but it sounds way more complicated than that. Unfortunatly I'm not too much of an electronics person although I'm study on it every day to learn the basics because I'm eager to learn. The PIC sounds very good but programming it sounds difficult at this point.

Thanx!
jevries is offline Find More Posts by jevries
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Could I use a Mabuchi 540 RC Car /Novak ESC for a plane? NetForce2K Foamies (Kits) 7 Apr 30, 2003 12:48 PM
Bushing size on a RC Car motor ? Kevin Murray Electric Plane Talk 2 Jan 23, 2002 02:31 PM
Can I use Speed 550(RC car motor) and sub C cell in Graupner Cumulus? Magna Electric Sailplanes 5 Oct 08, 2001 12:54 PM