Some newbie question for an Engineering Project

Hi Arduino Forum people!

I am looking for some help and guidance if possible about how to use these circuits with servos to control their movement with a potentiometer.
For a small engineering project I'm working on I need to be able to control a pair of servos with 90 degree potentiometers but have 180 degrees of travel on each servo for a motorised vehicle project.
This would involve one servo for throttle and the other for brakes.

Some sort of a fail safe system would be preferred where by, if there's a cutoff in the power supply the servos return to a throttle closed, brakes on position. However this does not have to be included because I could back this up mechanically with solenoid valves etc.
If this fail safe feature however was possible could a simple emergency push button be included?

Sorry if this is a really simple request but I'm mechanically inclined and haven't really got a clue when it comes to electronics but I'd love to learn!
Many thanks,
Tom

6239chester:
Hi Arduino Forum people!

Some sort of a fail safe system would be preferred where by, if there's a cutoff in the power supply the servos return to a throttle closed, brakes on position. However this does not have to be included because I could back this up mechanically with solenoid valves etc.
If this fail safe feature however was possible could a simple emergency push button be included?

Many thanks,
Tom

I think that would require a spring return mechanism of some sort.
The downside is the servo would have a higher current draw to counteract the spring.

I need to be able to control a pair of servos with 90 degree potentiometers but have 180 degrees of travel on each servo for a motorised vehicle project.

That's no problem Software controls the servo and software reads the pot. It's just a matter of what (if anything) the software does with the pot reading.

Some sort of a fail safe system would be preferred where by, if there's a cutoff in the power supply the servos return to a throttle closed, brakes on position. However this does not have to be included because I could back this up mechanically with solenoid valves etc.

That almost has to be mechanical because if the if you loose electrical power, nothing's going to work. :wink: That's my understanding of how air breaks work... Air pressure holds the brake off against a spring. You apply the brakes by releasing air pressure, and if you loose air pressure the brakes lock-up.

If this fail safe feature however was possible could a simple emergency push button be included?

In software, that's a simple if-condition. But for a "fail safe" that has to work with a software crash or power failure, etc., of course it has to be mechanical or an independently powered system, etc.

Have you looked at the servo sweep example program that comes with the Arduino IDE.

You will almost certainly need to use millis() to manage time as illustrated in several things at a time.

I would go for a fail safe system that disconnects the throttle or switches off the engine separately from the Arduino - perhaps a solenoid that needs electric power to keep the system ON. Something similar for the brakes.

...R

Thanks for the quick replies!
Don’t worry about the fail safe cause that can be catered for mechanically.

So just check with the software it can happily read a 90 degree input from the pot and operate the servos at 180 degrees, i.e. 2:1 ratio?

If the motor is ic there are devices made for aeromodelling that do this, they have their own rechargabale battery operating off the main supply, they operate on loss of power

6239chester:
So just check with the software it can happily read a 90 degree input from the pot and operate the servos at 180 degrees, i.e. 2:1 ratio?

Yes
But this is something you should easily be able to test yourself. The Arduino is a great system for learning-by-doing.

...R

I would run a relay through the ignition wire as a kill device. That way if the arduino isnt on the engine cant be either... And if you set it up so there is a mechanical fail safe on the brake it should be fearly safe

Also look up the map funtion it will be ur freind