Reversing a DC motor without sensor/external signal - Electronic Circuits Projects Diagrams Free

menirva · 13th January 2008, 03:46 AM

Anyone have any idea on how can i make this possible? For example a 2 wheeled robot bumped to a wall, then after few second it will start reversing.

Can anyone give me some idea how can i start to do this? Thanx!

weegee · 14th January 2008, 09:47 PM

i cant give you a circuit, but i would imagine that you would be monitoring the motor current. when you hit a wall, the motor will stall, at which point it will draw more current. when you get this current spike, you.... depending on configuration, but if using a relay to control direction, you would trip the relay to reverse direction. i imageing you would have to filter out the first spike after changing direction to avoid the starting current to the motor causing it to reverse again.

these are just whats bouncing around my head, and untested, so please go easy if ive made an obvious mistake.

**Nigel Goodwin** · 15th January 2008, 09:48 AM

Bumper switches - that's all most use, as it bumps a wall it presses a switch under a bumper, and that tells the circuit it's hit a wall.

menirva · 15th January 2008, 01:11 PM

wow thanx! i'll try all this idea this week.

weegee · 15th January 2008, 08:26 PM

Quote:

Originally Posted by Nigel Goodwin

Bumper switches - that's all most use, as it bumps a wall it presses a switch under a bumper, and that tells the circuit it's hit a wall.

i thought from the thread title that you couldnt use a switch 'Reversing a DC motor without sensor/external signal '

obviously if you can use external input then nigel is spot on!

Wingmax · 15th January 2008, 10:17 PM

Quote:

Originally Posted by weegee

i thought from the thread title that you couldnt use a switch 'Reversing a DC motor without sensor/external signal '

That's what I thought too. I thought this is going to be a hard one, how does the robot know when it hit something if no sensor is used.

menirva · 15th January 2008, 11:34 PM

I also thought about the 'overload' current. When the robot hit something, the motor will draw more current. I thought i can use this to make as a signal. But is there any comparator for current? Pity me now i only know how to use voltage as signal, i can use inverter for example.

weegee · 16th January 2008, 12:58 AM

not sure this is right, as im an 'experamentalist' when it comes to electronics, but i would assume that youd run the current to the motor thru a shunt, then measure the voltage drop accross it. but as i know many people on here know the theory inside and out, im sure someone could elaborate.

Wingmax · 16th January 2008, 05:01 AM

I don't know the application of this project, but won't it be much easier to use sensor or switch?

kurt_issac · 30th March 2008, 07:58 AM

I have decided to use a switch to trigger an external signal.

forum1.JPG

How to design, so that the motor will reverse when received HIGH INPUT from the oscillation? I have a reason why the T_LOW must be longer than T_HIGH.

kurt_issac · 30th March 2008, 08:24 AM

forum2.JPG

The problem with my design now is, the current_a period is too long. I want the current_a period to be the same as current_b

Diver300 · 30th March 2008, 10:48 AM

Your oscillator circuit seems over-complicated and also seems to have a design flaw. It relies on Q1 and Q2 not having too much gain.

It would be simpler to get rid of Q1, Q2, R2 and U2A.

Just wire R1 from input to output of U1A, with C1 connected from the input of U1A to ground.

http://www.fairchildsemi.com/an/AN/AN-118.pdf, figure 6 shows how it is done.

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13th January 2008, 03:46 AM	(permalink)
menirva	Reversing a DC motor without sensor/external signal Anyone have any idea on how can i make this possible? For example a 2 wheeled robot bumped to a wall, then after few second it will start reversing. Can anyone give me some idea how can i start to do this? Thanx!

14th January 2008, 09:47 PM	(permalink)
weegee	i cant give you a circuit, but i would imagine that you would be monitoring the motor current. when you hit a wall, the motor will stall, at which point it will draw more current. when you get this current spike, you.... depending on configuration, but if using a relay to control direction, you would trip the relay to reverse direction. i imageing you would have to filter out the first spike after changing direction to avoid the starting current to the motor causing it to reverse again. these are just whats bouncing around my head, and untested, so please go easy if ive made an obvious mistake.

15th January 2008, 09:48 AM	(permalink)
Nigel Goodwin	Bumper switches - that's all most use, as it bumps a wall it presses a switch under a bumper, and that tells the circuit it's hit a wall. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

15th January 2008, 01:11 PM	(permalink)
menirva	wow thanx! i'll try all this idea this week.

15th January 2008, 11:34 PM	(permalink)
menirva	I also thought about the 'overload' current. When the robot hit something, the motor will draw more current. I thought i can use this to make as a signal. But is there any comparator for current? Pity me now i only know how to use voltage as signal, i can use inverter for example.

16th January 2008, 12:58 AM	(permalink)
weegee	not sure this is right, as im an 'experamentalist' when it comes to electronics, but i would assume that youd run the current to the motor thru a shunt, then measure the voltage drop accross it. but as i know many people on here know the theory inside and out, im sure someone could elaborate.

16th January 2008, 05:01 AM	(permalink)
Wingmax	I don't know the application of this project, but won't it be much easier to use sensor or switch? __________________ May the force be with you. My project: Simple White Line Follower http://au.youtube.com/watch?v=8Z_MmrdH4oc http://i271.photobucket.com/albums/j...nefollower.jpg

30th March 2008, 07:58 AM	(permalink)
kurt_issac	I have decided to use a switch to trigger an external signal. forum1.JPG How to design, so that the motor will reverse when received HIGH INPUT from the oscillation? I have a reason why the T_LOW must be longer than T_HIGH.

30th March 2008, 08:24 AM	(permalink)
kurt_issac	forum2.JPG The problem with my design now is, the current_a period is too long. I want the current_a period to be the same as current_b

30th March 2008, 10:48 AM	(permalink)
Diver300	Your oscillator circuit seems over-complicated and also seems to have a design flaw. It relies on Q1 and Q2 not having too much gain. It would be simpler to get rid of Q1, Q2, R2 and U2A. Just wire R1 from input to output of U1A, with C1 connected from the input of U1A to ground. http://www.fairchildsemi.com/an/AN/AN-118.pdf, figure 6 shows how it is done.