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Author Topic: Axon servo control inaccuracy: need servo controller?  (Read 4444 times)

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Offline klimsTopic starter

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Re: Axon servo control inaccuracy: need servo controller?
« Reply #30 on: May 09, 2011, 04:29:38 PM »
It really comes down to trying to put a gallon into a pint pot - can WebbotLib control tens of servos, motor controllers, GPS, etc etc as well as the core logic of your program all at the same time? Well - yes it can. But your controller can 'squeak at the seams' - not a limitation of WebbotLib - just a limit as to how much you can ask a single cpu to do at the same time.

Makes sense. I was hoping it may have been possible  :)

You could just connect the Pololu controller to the Axon via USART, thereby gaining both advantages.  And the more accurate statement is that Webbotlib can control servos without jitter, just not while actually trying to do something else.

Yep this is my current setup, although I want to make a few changes as per my other thread. I want a single unit to be capable of servo control and dynamic gait control, like my Axon/Pololu setup is capable of at the moment.

but it begs the questions as to why you would use a $100 controller to control servos when you can buy dedicated servo controllers for a fraction of the price.

I have only been using my Axon and webbotlib to test if an ATmega equipped with webbotlib would be able to get the job done. I intend to build my own controller.

I remember reading somewhere on SoR that someone had ported a real time kernel to the Axon but I can't seem to find the post. I'm pretty clueless when it comes to real time stuff but would a hard real time kernel be up to the task?

At this stage I'm thinking that my easiest option may be to make a mini ATmega piggyback board for the servo controller to do what my Axon is doing at the moment.


thanks for the input guys

Offline Webbot

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Re: Axon servo control inaccuracy: need servo controller?
« Reply #31 on: May 09, 2011, 06:50:02 PM »
I remember reading somewhere on SoR that someone had ported a real time kernel to the Axon but I can't seem to find the post. I'm pretty clueless when it comes to real time stuff but would a hard real time kernel be up to the task?
Haven't tried it but my belief is that is that may actually be worse - as its effectively a smalk kernel that is using a clock and/or other interrupts to swap between execution threads. Since its 100% built on top of interrupts then thats why I assume it would be worse. The only way to get perfect timing is not to have any interrupts running at all.

Edit: other alternative is an 'intelligent' servo like the Dynamixel AX12 which effectively has a servo controller built into each servo. They are 'beautiful' devices - but do dent the wallet !
« Last Edit: May 09, 2011, 06:53:36 PM by Webbot »
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