motor reversal

Status
Not open for further replies.
dknguyen said:
BRAKING:
But if a DC motor has it's two terminals connected together it will brake. So if you want the motor to coast to a stop, just disconnect power. If you want it to brake, disconnect power and connect the two terminals together.
Click to expand...

Can a DC motor brake?? Stop immediately?? Is it really that simple? just connect two terminal together??
 
bananasiong said:
Can a DC motor brake?? Stop immediately?? Is it really that simple? just connect two terminal together??
Click to expand...

Not IMMEDIATELY, but it does stop very quickly, it's a standard technique that's been used for years and years.

Easy to demonstrate, just get a DC motor in your hand and spin the motor, it spins quite freely - now put a short across it, and spin again, it's now FAR harder to turn.
 
When the motor spins it generates a back-EMF. If you short the two terminals, then it forces the voltage difference between the two terminals to zero. A motor only has zero back-EMF when it's not spinning so it kind of forces the motor to stop (something like that, anyways I think).
 
How about this type of stopping?
10 or 01 is given to stop the DC motor, will it stop quickly? Or just same as removeing the supply, slowly?
 

Attachments

  • 01.GIF
    6.2 KB · Views: 192
bananasiong said:
How about this type of stopping?
10 or 01 is given to stop the DC motor, will it stop quickly? Or just same as removeing the supply, slowly?
Click to expand...

Looks like it does the same thing as shorting the circuit terminals. It stop quickly.

Disconnect motor power & short motor terminals = fast brake
DIsconnect motor terminals and leave terminals unconnected to each other = coast to a stop.
 
dknguyen said:
Looks like it does the same thing as shorting the circuit terminals. It stop quickly.

Disconnect motor power & short motor terminals = fast brake
DIsconnect motor terminals and leave terminals unconnected to each other = coast to a stop.
Click to expand...
Yes, thank you so much.
 
ah thanks heaps fellas this is really starting to make sense

there are many H-Bride types i have only just discovered....

i would have thought they all do the same job....
 
When the motor spins it generates a back-EMF. If you short the two terminals, then it forces the voltage difference between the two terminals to zero. A motor only has zero back-EMF when it's not spinning so it kind of forces the motor to stop.
Click to expand...
is this explaination correct??
 
It's kind of a hand-wavy explanation. Here is an article I found online.


So this would suggest that after you disconnect the power from the motor it is free-spinning on inertia and acting like a generator. If you short the motor terminals, it is like the generator is driving a low-impedence load (which is really hard to drive). Since the motor must work so hard to produce a large enough current across the short circuit to achieve the "generator-voltage" across the short-circuit, it slows down.

I think I incorrectly used the word back-EMF when I should have been using the voltage generated by a motor when it free-spins.
 
Last edited:
Thank you very much!!
 
Status
Not open for further replies.

Similar threads

B
Motor Reverser
Replies
5
Views
1K
bob4bvm
B
O
  • Question
DC motor not spinning with L293D motor shield
Replies
5
Views
2K
tepalia02
T
E
  • Question
Motor Controlling Circuit
Replies
10
Views
2K
MaxHeadRoom78
B
  • Question
wobbling polygon motor
2
Replies
33
Views
6K
rjenkinsgb
R
  • Question
Need help with that cranky motor controller again ..... Sorry
Replies
17
Views
2K
ramblin
R
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…