Grounding robot's aluminum frame

[electrofan]

Hello guys,

I am wondering if there are any problems/issues with hooking up my ground VSS to my robot's aluminum frame. It seems like it would be useful, but any problems other than shorts if other parts come into contact with it?

On another note, what's a recommended H-bridge for running 4 x 6V 700mA motors, using 3.3V logic? I'm currently considering the L298N.

Thanks

[TrickyNekro]

It's actually, good to ground the casing...

Protects from various RF, if any, and if disturbing... But still it's common and good to do so ;-)

[electrofan]

Ok thanks, that's good then.

Regarding the H bridge, I need to have both speed and direction control. I can either use PWM on the H bridge enable pin, or on its inputs (which would require 2 PWM signals). Right now, the plan is to use PWM on one input pin and use an inverter on the same PWM signal and pass it to input2, called 'locked antiphase' control. Any other ideas/recommendations? I've heard of other types of motor driver chips, are they any different than H-bridges?

[TrickyNekro]

I would clearly prefer the input over the enable...

From what I have seen in a scope, the enable lines some times have considerable rising times... Producing a oscilating something like signal...

The signal was far more predicted when PWM on the input, rather than enable...

Effective PWM signals for DC motos are somewhere near 10 - 15kHz... Personally even as high as 20 - 22kHz, which is good cause is beyond the human hearing range. This is something you should chooce depending on the inductance of the motor.

And depending on the inductance of the motor it's best to use a capacitor between the motor leads AND each lead and the motor casing, so that energy stored at the LC system, which could be of even 100V, can be driven elsewhere and not the H-bridge ;-)

I haven't really studied how all these methods are called, but there are actually some very nice tutorials out there....
Also... you are probably considering an IC and not power transistors or Mosfets right???

[electrofan]

Hey thanks for all the info. Yeah from my research locked-antiphase control seems to be more precise, with the downside of more energy loss compared to sign-magnitude control (aka enable pin PWM).

Right now, I'm planning on using an L298 H-bridge IC, but if you know of something better (smaller preferably, even surface mount) and more efficient, let me know.

[TrickyNekro]

The L298 has a nice multiwatt 15??? package, I don't remember the name exactly, which is indeed an SMD component.

Also look for the HB25... it has a single H-bridge IC that handles many amps ;-) and is SMD ;-))

http://www.google.gr/#hl=el&source=hp&q=VNH2SP30&aq=f&aqi=g1&aql=&oq=&gs_rfai=&fp=8cffb67ccaae3c44