how to create a small brake for a toy car ?

[navien_ra]

flayweel

my mini project is to detect an obstacle( if any) present before the vehicle and apply brake correspondingly.i am trying to implement this in a toy car.i need some ideas to help in creating a brake for that toy car( not a battery operated toy car, but a normal push type car)

 

[IanP]

So do you have any electricity available in your toy car and if yes what is U(voltage) and I(current) that you will allow for this break?

 

[gidimiz]

Hi,

If you are not using a power source, then you will have to use a spring or something that you will have to wind and then the energy stored in the spring will activate a device to brake the car.

If you ware building some other way to detect the obsitcal then use must be usign some kind of a power source, and if so then there are few ways to break a car, but all of them you will need to use your power surce.

The most simple way that i can think of top of my head, is to use a coil of a standert realy to bush another matel that will make some frection on a flay weel thats connected to one of the set of your weels in your toy car.

For beeter ideas, i need to know what type of energy you are going to use to break, machanical or eletrical.

Good luck.

 

[navien_ra]

actaully i am leaning PIC microcontroller(P16F84A - version).i have to implement this module in it. i am using an IR sensor to detect the obstacle,once an obstacle is detected , an interrupt occurs for PIC, now this PIC microcontroller has to trigger the braking circuit.the output voltage the can obtained from PIC in response is abt 5volts.so i had to design an braking circuit that can be activated using this 5 volt .this is how my mini project look like.since i am from electronics background, i am not familiar with advanced braking methods, but i know some simple braking techniques.i need ur help in igning a good braking circuit for a small toy car.

 

[Lepidoptera_ece]

What motor are you using? Since you are using PIC micro you have a lot of ways altering your motors rotation... if you are using a stepper motor... you just have to slow down the steppin method... but if you are using a simle motor... maybe you can build a simple circuit in which you can reverse the rotation.... apply a reverse votage in PWM to somehow slow down or stop the motor....

 

[gidimiz]

Hi navien_ra,

Lepidoptera_ece wrote some very good points. I do write code for Few MCU and its not a problem having 5V from the output of your PIC, there are many way to over come that. But what we all need to know and it is very importnat that you will answer all this questipons:
1. What type of battery are you using and how many if you are using few of them.
2. What motor are you using to drive the car. Votage, size and type of drive ( PWM or just a simple one )?
3. What type of sensor are you using to detect the object ( not so importnat question, but we can give you few ideas about that also ).

Any other information will just help us to answer your question better.

 

[navien_ra]

i have not yet decided about the type of motor to be used.i am still in dilema either to use a stepper motor or an ordinary one. can u suggest me which could be a better option ?as far as sensors are concerned ,i am using an IR receiver, ( with siemens detector ).for intial testing purpose i am using an 12 volt adaptor, but when this is implemented i may have to use an battery.

 

[gidimiz]

Hi,

Ok. So lets start:
Motor:
1. Useing an ordanery motor, that will be the most simple way for you to build the design. to implament a break, the all you need to do is turn the motor back for few micro seconds. The problem with this is that you cant know how much you have to drive the motor back to stop the car. You can over come that if you will put a sensor to know if you are going forwared or backword. then if you want to break, you break as long as sensor is in forwared.
2. Useing step motor: a bit more harder to implament with the software and uses more componantes. but will be much easier to break and you will not need to implament a direction sensor.
I would go with option 2, you can do much more with a step motor. change the spped, have more turqe at lower speeds, and break very fast.

3. Power. Try to build your circuit around the 4.5V. so get all compannets to be with that voltage raiting. If you will use higher voltage, then you will need to implament voltage regulator to lower the voltage to the PIC and other parts and theat just losing energy.
Good luck.

 

[M!k]

1. Useing an ordanery motor, that will be the most simple way for you to build the design. to implament a break, the all you need to do is turn the motor back for few micro seconds. The problem with this is that you cant know how much you have to drive the motor back to stop the car.

much simpler: cut off the power from the motor and short-circuit the motor. It will stop immediately. This can be done by using a small relay with a change-over switch, controlled by the PIC.


Mik

 

[gidimiz]

much simpler: cut off the power from the motor and short-circuit the motor. It will stop immediately. This can be done by using a small relay with a change-over switch, controlled by the PIC.


Mik

Never tried it before or saw someone using it.
Maybe?
Have you ever tried it?
If someone did use this kind of configuration please post.
Thanks.

 

[truebs]

After reading your project details ,the best design i could think of is to use electro-magnetism.

Have some magnet on the wheels and get opposite oriented magnet or electromagnet into the lever of the break.
So that it develops a magnetic friction to the motion of wheel.

Hope you can develop this idea further if found useful.

Regards.

 

[gidimiz]

Hi navien_ra,

I checked it and yes, what M!k said is correct. You just need to connect the 2 wires of the motor, and you will get an instant break.
Good luck.

 

[eltonjohn]

hi guys ..
I'm actually looking for a similar solution i need to stop a dc MOTOR ,but my problem i tha i need to stop it a an exact position .. because my motor drives a MIRROR and i need to get the same angle every time ..
Any ideas??
By the way i tried the short circuit thechnique and it won't work with my regular DC MOTOR it probably has too much momentum!

 

[snake]

try to use some encoder build by your self than you can know if the mirror are or not in the angle that you want, if not you can correct it .

sorry about my poor english.

 

[platonas]

EltonJohn,
You can use a servo motor mechanism.

Now about the topic, in order to stop a DC motor, the method suggested by Mik is the simplest and it is used in the portable power tools. The good quality electric drills and/or screw drivers use this methode to stop the chuck upon release of the trigger.

 

[eltonjohn]

well yes i think that i ultimatly will have to implement a SERVO type with PID ..
I will change my motor type to BRUSHLESS .. maybe with this type is easier to detect the position and somehow block it between 2 phases

 

[banh]

Hi navien_ra,

I checked it and yes, what M!k said is correct. You just need to connect the 2 wires of the motor, and you will get an instant break.
Good luck.

i dont understand how it works... does it work no matter how big the inertia of the car?

 

[gidimiz]

Hi banh,

Yes. What happens is this:
When you stop supply the motor with power, the motor becomes like a small power generator.
So if you connect the wires togather, the motor will convert the inertia of the car to power and supply itself with the power to turn it backwords, thus stoping the motor.
Makes sense?

 

[banh]

got it
how do u connect the 2 wires together ?

 

[rkodaira]

Hi !

It is only an idea.
I have some RC Cars models with methanol engine (0.5HP each). They have a very effective brake system: disk brake. The brake is commanded by a servo controlled by the radio receiver. The servo moves a bar which accelerates the engine (act on the carburetor) and in the other direction acts pressing two plastic plates against the disk (which is attached to a shaft linked to the 4 wheels). You can see the mechanical system in the manufacturer´s site (www.hpi.com).

These small cars weigh around 3kg and can reach up to 100km/h. There are RC cars that run with electric motors, but the speed control is totally electronic, maybe you can purchase one of this speed (and brake) controller, since it actuates over electric motors.