motor direction control 2

[simonbrewer]

What is the best way to control the direction of a 24V geared motor? I guess using a H-Brige is the way forward- i would like a push button to change the direction and another one to change it back again, i plan for the on/off action to be controlled by a PIR sensor! Any help would be greatly appreciated,

 

[VEBill]

What happens if you press both buttons at once?

DC motor?

PIR? Passive InfraRed? I love playing 'GTA'.

 

[analogkid2digitalman]

GTA- Grand Theft Auto?

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[simonbrewer]

Thanks for your answer,

It doesn't matter what happens when both buttons are pressed as this will never happen,
Basically the motor will drive upto a certain point where the first push button is depressed and then the motor will change direction upto another point where the second push button is pressed and hence the motor changes direction....and so on!--ideally i would like some sort of delay so that this does not go on for ever but i will probably settle with a manual switch off for simplicity but if you can help please do,

Yes i mean a Passive InfraRed sensor!

The motor is a Crouzet DC geared 24V reversible polarity

Thanks!!!

 

[VEBill]

GTA = Guess The Acronym
TLA = Three Letter Acronym

These are useful for 'returning fire'.


For back-and-forth motion, you can also look at mechanical solutions where the motor runs continuously in one direction. For example, I believe that all automobile windshield wipers use motors that simply turn in one direction while the wipers obviously go back and forth.

In fact, perhaps your project could be done faster with a visit to the local automobile scrapeyard.

With your approach, you may need to watch out for a huge current spike (worse than a dead short) if the current is reversed while the mass (rotating or linear) is still moving in the other direction. A small delay in between might be helpful (timing will be everything).

What does the PIR do again? Is it really 'P'?

 

[abcd3286]

It doesn't matter what happens when both buttons are pressed as this will never happen

HOGWASH How did you get so lucky to get perfect people??
ALWAYS design so you cannot engage both directions at same time.

 

[zeitghost]

I got the impression that the buttons were limit switches.

Is this corrrect?

 

[simonbrewer]

The application is a large robot which rotates at its 'hips', i have installed the motor and this drives the top half of the robot as required,I want it to rotate to a certain point then stop and turn in the other direction,

The infra-red sensor will be the trigger for this movement,

Yes VE1BLL i had thought about the current spike and have seen circuits with prevention against this, infact i have seen circuits which will could suit my project however they are for 12V power supplies and i need it to run off 24V,

I am afraid i am not too good at circuit design and am more a software man

Thanks again

 

[bill318]

Simon,

Have a look at the microchip web site for their ap notes on motor control. If it is a DC brushed motor your talking about (i.e. two wires only), then the H-bridge should work just fine. When you just say a 24V gear motor, the reader does not know if you are talking AC, DC, brushed or brushless.

You could use limit switches that trigger when the max movement in each direction is obtained. Run the limit switch triggers to a micro along with the trigger from your PIR. Most PIRs have dry contacts so you basically would have 3 switches to debounce in the micro and then the micro could in turn drive the H-bridge. Since you are using a gear motor, it will probably over-run a bit when power is removed, so have your limit switches cam operated so that they are not used as physical hard stops. You might be able to use a PTC poly-switch to break the motor current path should a hard stop be encountered.

Bill

 

[zeitghost]

Presumably you could brake the motor by turning off the top two transistors of the H and turning on the bottom two transistors.

Then when the thing has ground to a halt, you can reverse it.

Don't know if that would reduce the current spike.

 

[simonbrewer]

Thanks Guys,

I'll take onborad what you have all said and give it a go!

Si