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### Topic: RC car dose not move straight  (Read 1 time)previous topic - next topic

#### danaZayed

##### Apr 01, 2017, 04:43 pm
i have a rc car the electric one , the one can children set on it

when i control it by the remote control just give it straight , it dose not move straight it keep drift in right or left but most of the time it drift to left

the back wheels one of them has DC motor and the other wheel is free just it is moving while the car is moving

and in the front there is DC motor in the middle of two wheels

here is a photo of the car

Dose anyone have suggestion how to solve this problem ?
one of the solution that i tried is using PID with DC motor and compass
so the compass will let me know when the car is drift then i send specfic duty cycle to front DC motor , but the car keep moving in zigzag this is not good at all , what do you think if i replace DC motor with servo it will be better ?

also how to know the values of  PID gain it is too hard to keep trying

#### PaulS

#1
##### Apr 02, 2017, 12:48 am
Quote
Dose anyone have suggestion how to solve this problem ?
Get in your car. Find a straight road. let go of the steering wheel. Just how straight does your car go? For how long?

How do you cope with THAT problem? The answer is feedback. You MUST have some way of knowing that the car has drifted from the desired direction, which way, and how far. Then, you steer to correct the drift.

#### whitebank

#2
##### Apr 03, 2017, 04:41 pm
can i see your car? i guess friction of wheels are not equal together, that's why it turns left or right when 2 wheels rotates.

#### Southpark

#3
##### Apr 08, 2017, 06:02 am
i have a rc car the electric one , the one can children set on it

when i control it by the remote control just give it straight , it dose not move straight it keep drift in right or left but most of the time it drift to left

the back wheels one of them has DC motor and the other wheel is free just it is moving while the car is moving
In regular cars - like the ones we drive, with petrol. They do have such services as wheel balancing and alignment etc. So that when we drive and we keep the wheel steady, the car will at least drive 'relatively' straight - up to a point, and up to a limit that is. Beyond that, the driver makes the subtle control inputs to keep the car pointed in the desired direction. As you notice, the steering column of regular cars has at least some resistance, so that it doesn't slop around all over the place. So some friction, and some damping etc can help with stability.

Each drive wheel being at the same (or very similar) speed can help as well. And you mention 'RC' as in remote control. It also helps to be able to calibrate the controller - so that if nobody is touching the joystick, then what digital values is it sending to the car? If the value aren't calibrated or 'zeroed', then the car could drift.

And also, one typical feature used in some RC cars etc is to deliberately set a small range of values for which relatively small joystick inputs can be ignored. So if the joystick digital values are less than say +50 or -50, then have the driving algorithm convert values within this range to ZERO. And make the driving algorithm only response to joystick values above and below 50/-50 etc.

#### TheBlindMonk

#4
##### Oct 02, 2017, 01:37 pm
If it's not a secret, how did it end?

#### TheBlindMonk

#5
##### Oct 02, 2017, 01:43 pm
RC cars - that I want to buy but not sure that there won`t be problems with controls or smth else.

#### hammy

#6
##### Oct 09, 2017, 01:10 pm
If it only drives one wheel it will tend to drift , you might be able to compensate by looking at the alignment of the axles , the caster angles and any toe in of the front wheels.

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