Let's Make Robots!

H-bridge braking with L293(D)

I discovered how much braking power a Solarbotics GM9 can have when you short the terminals. I need that stopping power to make a robot that is suspended from a wire, wound around a spool, powered by a GM9.

But I also need to be able to power the motor in either direction. My platform of choice is the Picaxe 28 project board with a L293D motor driver chip.

How do I tell the L293 to short the terminals of the motor? I tried
high 4 high 5 ' both inputs high
low 4 low 5  ' both inputs low
but my motor will not brake.

Must I use the enable/disable pin on the L293D as well? Or should I get rid of this chip and get one without the internal flyback diodes (L293 without D)? Is a relay in order to tie the terminals together outside the main circuit?

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This explains why my motor will slowly drop, even when the terminals are directly shorted with a jumper. No speed means no energy to be dissipated. Hardly any speed (sagging) means hardly any energy to be dissipated and therefor no braking effect.

Pulling manually on the motor means enough speed/energy to cause a braking effect.

Braking (in terms of motor control) means slowing down, not to be mistaken for the parking brake on your car which will prevent it from rolling off a sloped parking spot.