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Best way to reverse a DC motor

IzaakTJ

New Member
Hi all,

I am participating in a design challenge where the aim is to build a repeatable vehicle. The vehicle must be fully automated once it has been turned on. The vehicle is also small, being no more than 400x400x400mm.

One main section of the brief is that the vehicle must travel to a wall, reverse direction and return to its original location.

All I need is a simple circuit that will allow for a button to be pressed against the wall which will then reverse the polarity of a small DC motor. I was wondering whether this would be possible with just a DPDT switch, or, because of the motor, a DPDT relay will be needed. I want to keep it as simple as possible, so just the switch would be preferred.

Many thanks.
 

MaxHeadRoom78

Well-Known Member
So you would also need a way of recording the distance to travel back to, some kind of rev counter/rotation sensor on the motor.
If only needing to do it with a DPDT switch, it would need push-on/push off style switch.
Max.
 

canadaelk

Active Member
Ideally a motor would come to a complete stop before rotation reversal. Especially true for larger and DC motors. E
 

Grossel

Well-Known Member
Well - frankly he can manage without a switch - assuming measuring the current of the motor (after a start up delay of course) and hence feed further to a logical function.
The downside here is that the vehicle will slam crash into the wall. Probably not the best idea but very possible.
 

gophert

Well-Known Member
Most Helpful Member
So you're just going to crash into the wall with no sensors to control speed/braking as you approach the wall?
 

shortbus=

Well-Known Member
Most Helpful Member
Ideally a motor would come to a complete stop before rotation reversal
In an ideal world that would be true. But I don't live in such a world.:) And it is done quite often, the reversal of DC motors without coming to a stop.
 

Grossel

Well-Known Member
So you're just going to crash into the wall with no sensors to control speed/braking as you approach the wall?
The task didn't say anything about "stopping before wall", so maybe building the vehicle more sturdy is a valid way to win the competition?
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
if you use an "H-bridge" and wheel sensors, you have what you need.
Some can do, FWD, REV. Brake and coast. You can vary the speed of the wheels to effect turning.
 

gophert

Well-Known Member
Most Helpful Member
The task didn't say anything about "stopping before wall", so maybe building the vehicle more sturdy is a valid way to win the competition?
Maybe, maybe not. If the vehicle doesn't hit the wall perfectly square, and even if it does, the car may bounce out of alignment, roll or even get broken (or break the wall). It's a strategy and he's free to design it any way he wants. The organizer may disqualify him or may not. I have no idea. I only asked so I'm watching the correct part of the screen when it happens (my wife hates when I rewind and watch a second time).
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Maybe it's a line following robot. Follow the line, use an ultrsonic sensor to find the wall. Slow down, stop, reverse direction, go back home. magnetic hall effect switch at start,
 

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