Hi John,

On Thursday, September 15, 2016 at 3:30:31 PM UTC+1, John Kasunich wrote:
> You mentioned the LMD18200, and I looked it up.  That is a chip, not a 
> complete driver.  It takes a significant amount of electronics knowledge 
> to make a reliable system, even starting with a chip like that which has 
> a lot of built-in functionality.  Power distribution, ground bounce, 
> common 
> mode voltages, choice of switching frequency, electrical noise, thermal 
> management, circuit board layout, etc, etc, are all non-trivial issues. 
> Because you mentioned a naked chip, I assumed that you were 
> comfortable with all those issues. 
> Fair enough - I have used that chip a few times successfully, but perhaps 
the applications were simple enough to avoid addressing the more complex 
issues you mention.


> That all depends on your needs.  What kind of force/torque fidelity 
> do you want? 
> I honestly don't know yet! I suppose I could try simulating a non-ideal 
force controller and see if I can still balance my pendulums

> In a one-off design, I would NOT use the chip-supplied current 
> feedback.  Many of the hassles of power electronics can be avoided 
> by isolating the control from the power.  I would spend the $10-20 
> for an isolated current sensor.  For example: 
> http://www.digikey.com/product-detail/en/lem-usa-inc/HO-8-NP-0000/398-1141-ND/4331974
That seems like a good tip - thanks

If the goal is to focus on the control of the pendulum, I would use 
> a simple hysteresis controller for the current.  If you want to get 
> into the minutia of motor control you could send the output of 
> that sensor to the controller's A/D converter and do the current 
> loop in software - although that would require MUCH faster 
> control loops relative to the pendulum control. 

I haven't actually heard of a hysteresis controller before. Is it a 
bang-bang controller with a deadband?

Thanks John.  

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