Mad Bull, fault - (runs on its own when controller is off)

[Paul N]

I purchased a Mad Bull car for my son Mike, (who is autistic), nearly 12 years ago. Mike could not get on with the controller unit and the car sat is a cupboard unused. I decided to purchased a new battery for the car and I now have a young grandson Charlie, who would love to get into car racing with the Mad Bull. The Mad Bull has a fault, when the controller (Controller - atoms TECHNIPLUS, Model No. AP-202, (27MHz) is switched off and the aerial retracted, the car sometimes decides to run on its own. You have to disconnect the battery, if you can catch the car. The controller has 3 lights, red, amber and green, which are lit all the time. The atoms (AM 2 ch receiver ) has a RX Band 5, (green) insert, and 2 sockets for ch1 and ch 2, plus batt connection. There are no other connection points.  Any help or suggestions would be appreciated. Regards Paul N.

[No Slack]

Has the car a mechanical 3-step speedcontroller? 

[Baddon]

when the car has no input it may do random things, you need to ALWAYS turn the car off first (switch OR better yet unplug battery - then turn of the controller.

The older radio gear is not great and a modern 2.4 set will be 30-40

[Percymon]

This sounds like the linkage /servo zero point for the speed controller isnt set correctly (assuming it’s an older manual controller). With the handset turned on the trims of the handset could be set sufficiently to move the MSC into a neutral position, turn the transmitter off and the msc servo resorts to its own neutral point, which may engage the contacts of the speed controller.

 

alwsys turn on the transmitter first, and turn it off last 

[Mad Ax]

Great advice here already, but it could also be that switching off the transmitter causes the throttle servo to move to some arbitrary point (other than neutral).  I think most modern radios will self-centre if they lose signal from the transmitter, but if my memory is correct the older 27MHz AM radios didn't do that, especially the AP-202 which was a budget radio.  Actually back in the day (when 27MHz was a common frequency for everything from walkie talkies to toy-grade RCs) it wasn't uncommon to switch on a receiver and watch the servos dance a little jig as they picked up stray signals from neighbouring bands.  You had to have your transmitter turned on to overpower the stray signals.

So basically this comes down to good practical advice - always turn on the transmitter before turning on the car, and always turn off the car before turning off the transmitter.  This should be in the manual but it's easily overlooked / forgotten if you don't do this stuff every week like most of us here  

It is also good advice to disconnect the battery immediately.  The on/off switch on the mechanical speed control does not provide any disconnection between the battery and the motor - that is done by the wiper arm connected to the servo.  So a car with the power switch in the 'off' position is just as live as a car with the power switch in the 'on' position, but arguably less predictable.  If someone accidentally moves the servo, the motor will run and the car will head off on its own agenda (or, if you're working on it, the tyres will spin and tip over that tub that you were neatly keeping all the screws in, and launch the instruction manual on the floor, and maybe graze your fingertips).  There's no spring-loading to assist the wiper arm back to the middle, so it won't stop until chemistry runs out or physics steps in.

[Wez-li]

Just as an aside, when I'm checking my electrics, I use a stand. 

No chasing cars, I don't like exercising outside my allotted times 

An upside down takeaway pot works just as well!

[rich_f]

I think you've got your answer now, but a couple of things left to say:

First, it's not a fault, although it may appear that way - this is what happens when using 27MHz radio gear. There is a lot of interference in that band. 

Second, if this happens again, i.e, if the controller is turned off before the car is powered off and it starts driving away, just turn the transmitter back on and the car should be under control again, so no need to chase it!

[Mad Ax]

23 minutes ago, rich_f said:

Second, if this happens again, i.e, if the controller is turned off before the car is powered off and it starts driving away, just turn the transmitter back on and the car should be under control again, so no need to chase it!

Lateral thinking of the highest order, there.

rich_f - thinks fast, remains cool under pressure, like an astronaut

[TurnipJF]

I got my nephew to remember the order of switching on/off by having him imagine the car as a naughty schoolchild and the transmitter as the teacher. If the schoolchild isn't being told what to do by the teacher, it will run of and do its own thing. So just as the teacher enters the class before the children and only leaves once they have gone, so too should the transmitter be turned on before the car, and only turned of again once the car is off and disconnected. 

[KEV THE REV]

You can also fit a fail safe to prevent any low batt run offs too