Parallax PSC -vs- Mini SSC II servo controller.
Dobermann (Black Dog Systems, LLC)
Posts: 71
Hello Everyone!
After trying to use the Scott Edwards Mini SSC II servo controller www.seetron.com/ssc.htm I've become more than frustrated with it. I was informed by a tech at Seetron, as well as for many other people on this forum (thank you for the replies), that it can be used with 'modified' servo's. It in fact can, but very badly. My problem is that the servo's I'm using must have slipped zero (750=off). Probably were bumped around alittle, while I did glue the pot it must not be holding. I know that I can workaround the issue with the stamp using 'pulsout = 757', that seems to be the new zero setting. However, the Mini SSC II controller upon powering up, tries to 'centre' the servo's attached to it. Since the zero position is never located, the wheels go 'round and 'round never stopping. This is presenting a problem, as you can see. Power on, 'bot is off and running with possibly no program loaded onto the stamp (BS-II). Chaos, total chaos could ensue, not to mention damage to 'bot, furniture, creator, dogs, the list goes on. I know that I could place an on/off switch to disable the Mini SSC II from powering up prematurely. But even so, that will still not really 'fix' the problem. Upon powering up it will still try to seek centre position. Unless the stamp were to tell the Mini SSC II early on in the power-up sequence to stop seeking zero. Is the PSC from Parallax going to make my life any easier? I'm reading the features list, as well as the associated documentation. It seems that no attempt is made by the PSC to 'centre' servo's upon powering up. Is this the fact or am I missing something. Its ashame, since I bought two of the Mini SSC II's at one shot, that I may well have wasted money better spent on the PSC. Your comments or recommendations are gratefully appreciated!
Respectfully,
Michael G. Jessat
After trying to use the Scott Edwards Mini SSC II servo controller www.seetron.com/ssc.htm I've become more than frustrated with it. I was informed by a tech at Seetron, as well as for many other people on this forum (thank you for the replies), that it can be used with 'modified' servo's. It in fact can, but very badly. My problem is that the servo's I'm using must have slipped zero (750=off). Probably were bumped around alittle, while I did glue the pot it must not be holding. I know that I can workaround the issue with the stamp using 'pulsout = 757', that seems to be the new zero setting. However, the Mini SSC II controller upon powering up, tries to 'centre' the servo's attached to it. Since the zero position is never located, the wheels go 'round and 'round never stopping. This is presenting a problem, as you can see. Power on, 'bot is off and running with possibly no program loaded onto the stamp (BS-II). Chaos, total chaos could ensue, not to mention damage to 'bot, furniture, creator, dogs, the list goes on. I know that I could place an on/off switch to disable the Mini SSC II from powering up prematurely. But even so, that will still not really 'fix' the problem. Upon powering up it will still try to seek centre position. Unless the stamp were to tell the Mini SSC II early on in the power-up sequence to stop seeking zero. Is the PSC from Parallax going to make my life any easier? I'm reading the features list, as well as the associated documentation. It seems that no attempt is made by the PSC to 'centre' servo's upon powering up. Is this the fact or am I missing something. Its ashame, since I bought two of the Mini SSC II's at one shot, that I may well have wasted money better spent on the PSC. Your comments or recommendations are gratefully appreciated!
Respectfully,
Michael G. Jessat
Comments
·· In fact, the PSC does center each servo on startup.· If it didn't do something like this, how would it know where to set a servo on power-up?· If your servos can not be centered properly then you would have to make setting new servo positions something that happens early in the startup code.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
I must have missed something in the documentation about the PSC. I kind of figured that it had to do some form of centre finding. Seems that every servo controller I've looked at does, like you stated how would it know where to set the new position to. Looks like I'm going to be opening up my servo's again. Thanks for your reply!
Respectfully,
Michael G. Jessat
·· The thing is, the PSC is constantly refreshing the servos whether you set a position or not.· This means that it has to send some value.· The best arbitrary value would be the servos normal center position.· I suppose an enhancement to the servo controllers would be a stored EEPROM setting for each channel, but that would really add to cost/complexity of the device.· Not many people would use it, I would guess.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
I would
I know I have seen a website that showed a 'demo' version of the Mini SSC II code. I can't seem to remember where, I'll search for it, maybe they are still online. It supported only 2400 baud, 1 servo operation, and required a PIC 12C672 or 12C675, don't remember. But it was 'actual' code that the Mini SSC II uses, they use an 'enhanced' version for the full SSC II. I have PIC Basic Pro Compiler and a burner. Hmmm, <scratches head, looks around workshop, wonders>. Maybe I'll make an attempt at building one just for this purpose. Thank you for your reply.
Respectfully,
Michael G. Jessat
I just have to ask.
Is it just me, or are there any others that would find a servo controller with the ability to store the servo 'centre' position (ie- 750 = centre) via an EEPROM? I'm currently researching the possibility of designing one. Since all the various controllers I've seen to date don't allow for a slight deviation in the servo centre position. I know that the quick 'fix' would be to just send a command to the servo controller via the stamp early on in the initailisation, to stop seeking 'centre'. But, for a brief moment, the servo controller would still activate and rotate the servos trying to find 'centre'. Chris Savage posted a response earlier in this thread, that is where the real idea came from. I'm just looking at bringing it to life.
Regards,
Michael G. Jessat
·· Your post/question is certainly welcome, but I think this might be something that is relatively low demand.· Servo Controllers greatly simplify things on the host controller end by taking care of the refreshing of the servos.· Unless disabled, the servos are always being refreshed.· Given that you can expect on power-on the need for a set value to be used for refreshing the servos (Random wouldn't be good).
·· Now, you can create your own controller, but you will need one with on-board EEPROM, something not all have.· This will be no small task either, as there are a lot of aspects to a servo controller.· We put a lot of effort into ours.· Won't be easy to start from scratch, but at least you have a few to model from.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
Take a look at the Pico Servio. It has onboard memory, along with the ability to store positions (pulsewidths in the continuous rotation world) and sequences. It also has the ability to send a command to turn the servos off (though I've not tested it).
http://www.picobotics.com/Products.html
Theoretically, the combination of the ability to turn them off programmatically, then have the initial command under your control might approximate having the servos start off somewhere meaninful.
To the great folks at Parallax - I would offer that, if you believe that walkers, multi-servo anthopomorphic and biology-inspired machines, and full-fledged humanoids are increasing in popularity (I do), then the kinds of features we see in the Picobotics product, the newer Lynxmotion servo controllers (coordinated moves) are going to become more and more common and in fact demanded.
Having now written some basic motion editing software, and ported the driver layer for both the MiniSSC and PSC, I can say for sure that these kinds of features greatly simplify the motion control world, and I'd love for my "one stop shop" (that's you guys) to compete reasonably with the niche folks.
Don't get me wrong - I love that there's still plenty of space out there for us garage inventors to innovate, but I think this part of the problem is ready to be scaled up.
Is there a forum where Parallax accepts organized input for feature requests on its products?
Michael - if you do go into invention mode - let me know and I'll make a list of features for which I'd be willing to pay 8-)
Regards,
-r
Thanks for the replies. I can certainly understand the complexity of this task. I'm a programmer, but, I am a novice with the electronics aspect. I have certainly learned alot about electronics, as it became part of one of my many jobs. But designing along with necessary layout work is something I admit, I'm next to lost. Give me a schematic, and I can build it, tell me to do it from nothing, and well lets just say it may, or may not work. I'm really researching this project as a possibility, if others were interested (Chris, you might be right about lack of interest), that I would glady share my information, freely. I'm going crazy with these servo's I have, they just don't want to behave. The additional feature that would make me very happy indeed, would be the EEPROM space to store an offset. I will pursue it until either A.) I have exhausted all my available resources, or B.) I get frustrated and give-up. Picobotics servo controller looks interesting. But, I think that what I could do by way of the BS-II, and the Mini SSC through programming, would be the same thing (sort of). I could simply send the Mini SSC controller a stop seeking centre command early on in the initialisation. I'll still welcome any nudges or pushes in the right direction. I'm in search of the holy grail!
Respectfully,
Michael G. Jessat
·· Please don't mistake my post for lack of interest.· There may be someone who can collaberate with you on this project, I just thought it seemed like something that might be somewhat unique to your situation, so however you go about doing it may or may not affect anyone else.
·· Again, that kind of came out wrong...I guess the bottom line is you should do it the best way that suits you.· Getting feedback wouldn't necessarily be the best thing since you will often get lots of feedback from sources which won't be using the device anyway, so that may not help you, and in fact may hinder you.
·· It's advice to simplify what you already hinted at being a somewhat daunting task for you.· I personally wish you the best of luck with it.· It's a very ambitious project, that's for sure.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
Thanks for the reply. I personally didn't take anything stated earlier in this thread as being negative. In fact, it is just making me see that the 'need' IS rather limited. However, I will still pursue it. Looks like I'm going to have alot of free time on my hands, I just lost my job today.
Respectfully,
Michael G. Jessat
·· Definately follow your goals, just don't let anyone else's goals interfere with them.· Once I worked on a piece of software for months, constantly adding in all the details that people thought it should have, only to find after a few months I asked for feedback on the functions, and nobody used them.· I wasted a lot of time adding things that weren't used.· Also I customized a few screens based on user input, only to find that other people later complained about complexity, and when shown my original screens they liked those better.· Point being, you gotta do it your way.· Only you will truly appreciate it.· If other benefit from it, BONUS!·
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Chris Savage
Parallax Tech Support
csavage@parallax.com
Thank you. I am still inspired, and will at least continue to research the possibility of making this project work. If it benefits no one other than myself, its still a benefit.
Respectfully,
Michael G. Jessat
Concerning your "floating servo center" position, Parallax may have provided an alternate solution in their current stock of continuous rotation servos. To prevent the developer from having to open up and re-center the servo OR to have to accomodate "floating" in code or with the PSC, they have proviced a small hole inthe servo case which allows one to adjust the centering pot. If these are the same servos that you describe in other posts as still having the electronics intact, perhaps you could drill a hole and mount the internal pot in such a way that re-centering would be a relatively minor task.
Just a thought...
Good luck!
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Truly Understand the Fundamentals and the Path will be so much easier...