   Electronics - modding RC car
  Hi,Last few days I've been experimenting with controlling a Radio Controlled car via the PC through a USB control board. All has gone well, including my first foray into soldering.However I found the 'cheap' RC car I bought to experiment with is actually too fast, it takes only about 2 seconds to travel from one end of my room to the other, which somewhat spoils the enjoyment.So i want to slow it down, but as the controls are digital not analog there is no variable control for the speed(acceleration). My initial though was to simply remove one of the 3 1.5v batteries and this worked it was slower and more controllable. Unfortunately the batteries not only power the 'engine' motor, they also power a motor (maybe a servo?) that controls the steering of the front wheels, meaning that the turning circle was greatly reduced.So what i'd like to try and do is mod the car slightly so that only 3v goes to the engine motor, but the full 4.5v go to the steering mechanism. This would be straight forward if i just added a new set of batteries to control the steering, but I'm not sure how simple it would be to add them into the control circuits.Another idea was to remove a battery from the compartment and some how add it in serial to the wires going to the steering motor. But i'm not entirely sure how to go about doing that or if its possible, adding it in parallel would be, but that would give the desired results would it?So i'm wondering if there is a good 'electronic' method for doing this, perhaps adding some component between the ground and +4.5v to the 'engine' motor, that would reduce its power. As you can probably tell I know little about electronics, probably just enough to be dangerous ;)Anyone got any suggestions?Actually now i come to type this up i wonder if there would be an easy way to control the amount of steering too. Since the power appears to affect how far the steering moves, if i could adjust the flow i could have analog steering. Mind you no idea how i could control this from the existing RC transmitter.Some photos I took whilst mod-ing the handset opened, circuit board front, circuit board back, finished
  Can you not adjust the gears on the car? Remove the motor and replace the gear cog with a smaller one, that will slow the car down while lengthening the indurance of the batteries.Also, your steering and throttle should be proportional, they asre joysticks on the control panel, the further you push the stick the more movement input is sent - there must be a way of tying this up to your PC input.On a side note, I used to race these things as a kid. Those were the days :D   ;  A quick and dirty way to reduce the voltage across a component is to put rectifier diodes in series with it. Each diode will (typically) have a 0.7V drop, so one diode will drop the voltage across the motor to 4.3V.If the car can go backwards as well as forwards, chances are that putting a diode in series will prevent it from moving in one direction, in which case you could use a bridge rectifier (1.4V drop). It may be worth trying to limit the current via a resistor instead.Edit: I have no idea why I suggested a bridge rectifier, as all that would do would make the car move in the same direction whether you were telling it to go forwards or backwards.[Edited by - benryves on September 17, 2008 1:34:40 PM];  Can this RC car go in reverse? If not than you can use the terminal between the two batteries (1/2 Voltage) to drive the common of the motor. If the motor can reverse than you would have to find the commons BEFORE the direction control circuit (probably 4 transistors or more). Sorry it's hard to tell without much to work on. Also the 2nd problem is that this would drain one battery much much faster than the other which will reduce time severely and may hurt the batteries. I can't think of much simpler solution at the moment.The ironic thing is that two days ago I started designing a circuit to make a remote-control RC car. I had an old radio-controlled car but some time ago ripped the circuits out of it, so I decided to rebuild it but better (analog speed + analog steering). Just waiting on some parts. :) (I know your goal is quite different but I thought it would be fun mentioning.)   ;  I say jimmy-rig it with a resistor on one of the wires going to the motor.  If you use a variable resistor (like one with a small knob attached) you could speed it up later on without having to re-solder anything.   ;  What about doing something like this?;  Blimey, don't remember ever getting so much fast response to a post.gavco98:Sadly the handset controller just uses 'tact' switches (like those for mouse button) operated by the levers (can't really call them joysticks), so its a boolean operation, either on or off, there is no variable control.Your cog idea sounds good, although this is a really cheap RC car, so not entirely sure it will be possible, but i'll have a look.Benryves:Thanks for the ideas. figured there must be some components built to do this, now i've got something to look for. DarkInsanePyro:Yes the car can go in reverse, it actually feels like its quicker than going forward, but perhaps thats due to excessive wheel spin.Sounds like fun building from scratch, but yeah i'm looking for a simpler hack/mod than doing all that. Odd thing, I can find loads of info on car parts and building, but very little about making the transmitter/handset with analog controls. I originally wanted to avoid mod-ing the actual car and just focus on hacking into the transmitter circuits/controls for ease.However this has gone so well (in terms that it works from my pc keyboard) that I might look to upgrade to a 'proper' rc car and see if i can get proportional control over the throttle/engine speed and steering as that would be far more satisfying. Then again i'm also looking at anything electrical wondering if I could hook it up to my PC, whether it needs to or not ;)Moe:So another vote for a resistor then, any suggestions as to the value to go for? It would also appear to be one of the simplest in terms of actual electronic changes to be made.JSoftwarePretty picture, looks intriguing, just no idea what those symbols represent ;)I'll have to go and look them up. But i assume the 'both directions' bit relates to being able to reduce the power for the motor in both forward and reverse directions?Thanks for everyones replies. if i have time i'll open up the car and grab some pictures from inside in case that helps, although at present i'm leaning towards going down Maplins tomorrow and buying a few resistors to try out.;  The arrow like shapes are diodes :)   ;  I have no idea about the actual resistance.  I'd try to find some old piece of electronic equipment where you can rip one off.  I think the one I've got came from the tracking adjustment on an old VCR.   ;  Rather than changing the gears, you could change the wheels I suppose.   