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car-like robot

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justas12

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Hello,

I need to made research 4wd mobile robot. The question is, has anybody information or ideas, about 4 motors synchronization? because when car do the angle, one wheel ir rotating slower than another in different side. How to control it? Maybe simulink model or science reviews? Because using google I dont find any suitable information.

Thank you...
 
The motors must not be synchronized when turning a corner.
Stepper motors synchronize very well and corners are hard.
Most electric motors are not synchronized and corners are easy.


Why do you want to synchronize 4 motors?
 
I can't use stepper motors. I think sinchronization is necessary when robot goes straight...It would be bad, if going staight one wheel rotating slower than the others.
 
I can't use stepper motors. I think sinchronization is necessary when robot goes straight...It would be bad, if going staight one wheel rotating slower than the others.

If the robot is going straight the wheels will be synchronize by the ground.
There is not a direct relationship between motor voltage and speed.

Example: If you have 4 motors that are 100% the same they will go the same speed, because the ground makes them and because they are the same and want to go the same speed. After a year one motor dies and you replace it with a new motor that wants to go 5% faster because it is new. All 4 motors see the same 12 volts. The new motor will be slowed down by the ground and the 3 old motors will be speed up a little by the ground. The new motor will pull slightly more current. The 3 old motors will pull slightly less current. The robot is good.
 
There is not a direct relationship between motor voltage and speed.
This is not quiet the fully story. If a motor is spinning the voltage developed across the motor's poles will be directly related to it's speed as long as it's not being driven by an external voltage, I ran across a motor controller PDF on net a ways back that used this as a way to get speed feedback from the motor, although not useful for synchronization the relation is direct.

When powered from a voltage source it's not direct but the motor's speed can be determined if the external load on the motor can be sensed as well, it's not however very precise.
 
You need a closed loop speed control on each wheel:
https://www.electro-tech-online.com/custompdfs/2012/03/PID-without-a-PhD.pdf

After you accomplish a good speed control of your wheels, you need a microcontroller or other embedded computer to calculate proper speeds for each wheel for a given turning radius. The calculations are fairly simple. Send the speed commands to each wheel and that is all the synchronization you should need. There will be errors in your geometry, wheel diameter etc. so don't try to get a perfect system. Proper tuning of the PID controller should be enough (and a good kinematic model).

If you wan't to study synchronization techniques, IEEE is a good place to start (if you have access). Start by searching wheel synchronization in two-wheel robots.
Something like this:
https://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1461413
 
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I need to made research 4wd mobile robot. The question is, has anybody information or ideas, about 4 motors synchronization? because when car do the angle, one wheel ir rotating slower than another in different side. How to control it? Maybe simulink model or science reviews? Because using google I dont find any suitable information.

One way is to use PWM and set the speed...
 
A PWM does change the speed, but the load has more effect than the duty cycle. example: a load can stall out any motor no matter what the voltage or duty cycle is.

How is the steering done? If it is done by changing the power on each of the 4 wheels?

A 4 wheel drive car does not sync the 4 wheels. In fact it has parts to allow the 4 wheels to turn independent.
 
A 4 wheel drive car does not sync the 4 wheels. In fact it has parts to allow the 4 wheels to turn independent.

Yes. Normally 4 wheel drive car has a Differential Gears on the back and rear axle. https://www.youtube.com/watch?v=K4JhruinbWc
I believe that in this case the 4wd robot will have one motor for each wheel.. like mars rover or something.

What I would like to know is: Are you (justas12) going to design and build the system, or do you need to do research and simulation on different kind of solutions?
 
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your link is not suitable for me...Firstly idea is to create synchronization model, for example the robot is going straight, but if one wheel enter the pit, how the controler sinchronyze all the system. The controller should give more power for this wheel. Forget the steering for a while.
 
your link is not suitable for me...Firstly idea is to create synchronization model, for example the robot is going straight, but if one wheel enter the pit, how the controler sinchronyze all the system. The controller should give more power for this wheel. Forget the steering for a while.

A real car does not give more power to a wheel in a pit.
 
I know that...But the task is that wheels would be spining at the same speed in all condition, and the one is when wheel in a pit.
 
Are you talking about traction control and stability control of the car?

I know that...But the task is that wheels would be spining at the same speed in all condition, and the one is when wheel in a pit.

When the car is going forward and a wheel drops in a pit, doesn't the wheel need to spin faster because it is traveling longer distance?

If all you need is a steady speed control, then all you need is an effective closed loop control for each wheel. The theory is pretty basic control theory.
 
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