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propeller servo controller problem — Parallax Forums

propeller servo controller problem

GumbaGumba Posts: 14
edited 2010-02-21 13:44 in Propeller 1
Hi, new to the forum.· I hope this is the right place to post my question.

I have a possible problem with my propeller servo controller:·

The set up:

Im using a laptop with Windows XP

the device is a Propeller Servo Controller USB, item 28830

I'm using VSA for servo control

power: usb cable supplies power to the controller board; an atx computer supply, 5 volt rail, powers the servos

Problem:

mini servo motors attached to the board work fine (for example, T Pro SG90).· Larger servos, such as T Pro Sg 5010 or slightly smaller attached to board will not respond--they twitch and jitter but do not responde to routines.· I tested the servos with an E Sky servo tester and they work.

Via VSA the·baud rate is set at 38.4k

Bad board?· Bad settings somewhere?·Any ideas?

Any advice you can give would be welcome.

Comments

  • hover1hover1 Posts: 1,929
    edited 2010-02-14 03:09
    This looks like a standard servo. We have had some problems with Digital Servos. Check out this link.

    ·http://forums.parallax.com/showthread.php?p=862005

    I'll check back.

    Jim
  • GumbaGumba Posts: 14
    edited 2010-02-14 03:42
    thanks for the quick response. yeah, all of the servos I have are standard---no digitals. I have about 7 of these T Pro servos that I just bought, all work on the servo tester. Hopefully there's a fix to this.
  • hover1hover1 Posts: 1,929
    edited 2010-02-14 04:16
    Try putting a 10k resistor·from the "W" output pin to the servo and see what happens. I have used a 1K resistor with good results on my JR Digital servos.

    Jim
    Gumba said...
    thanks for the quick response. yeah, all of the servos I have are standard---no digitals. I have about 7 of these T Pro servos that I just bought, all work on the servo tester. Hopefully there's a fix to this.
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2010-02-14 08:08
    Gumba,

    Can you do a sanity check for me and see if the Propeller Servo Controller will work at the lower 2400 baud default setting?

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • GumbaGumba Posts: 14
    edited 2010-02-14 15:04
    tried that. Same basic results--smaller servos respond but larger ones won't (though there is a definant decrease in response from the smaller servos when the baud is at 2400--sluggish).

    hover1, thanks for the suggestion. I have a basic understanding, but really am just getting into all of this--and need to practice my soldering skills before I start adding components to a $40 circuit board!
  • hover1hover1 Posts: 1,929
    edited 2010-02-14 15:49
    You won't find any room to solder a resistor on the board, you want to come off the header; after the voltage translators. I just used a couple of clip leads to connect the resistor to the servo for testing.

    Do you have a 6 volt or 7.2 volt battery to supply the servo power for a test? The specs on the servo say that it will take up to 8.4 volts.

    Jim
  • GumbaGumba Posts: 14
    edited 2010-02-14 16:10
    hover1--understood. and yes, I have a 6 volt lantern battery I could use.

    Just in·case it helps any the board is item 28830 and has "Rev A" stamped on it.

    Post Edited (Gumba) : 2/14/2010 4:19:00 PM GMT
  • hover1hover1 Posts: 1,929
    edited 2010-02-14 17:09
    Both of my PSCU's are Rev A as well.
  • GumbaGumba Posts: 14
    edited 2010-02-16 02:02
    I haven't tried adding a 10k resistor yet, though I plan to.· Even if this works I'm not thrilled about having to yank a wire from one of the output pins on every servo I want to use and·add a bunch of resistors.

    From other posts I've seen this seems to be a real problem on the newer boards.· Do the folks at Parallax have a·plan on how to fix these boards?·
  • hover1hover1 Posts: 1,929
    edited 2010-02-16 02:13
    I don't think it has been addressed yet, but I know they know about it.

    I have a plug·in board that I'm waiting to get from the manufacturer·that will add the resistors to all the outputs so I can run my JR Digital servos.

    Jim


    Gumba said...
    I haven't tried adding a 10k resistor yet, though I plan to.· Even if this works I'm not thrilled about having to yank a wire from one of the output pins on every servo I want to use and·add a bunch of resistors.

    From other posts I've seen this seems to be a real problem on the newer boards.· Do the folks at Parallax have a·plan on how to fix these boards?
    Post Edited (hover1) : 2/16/2010 2:19:13 AM GMT
  • GumbaGumba Posts: 14
    edited 2010-02-20 19:45
    I spoke with tech support and was advised to try updating the firmware before doing anything else. I've downloaded the the Spin Tool and the firmware. I can open the firmware and view it via the Spin Tool but am stuck at that point. Can anyone provide guidance on how to actually do this update?

    Sorry if this is a dumb question.
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2010-02-20 20:06
    Like all other propeller based platforms you have two options, press F10 and it will load the program in to the propeller's memory or press F11 and it will load the code into the propeller's memory and the EEPROM which will store the program so it loads every time the propeller powers up.

    You want to press F11, of course the usb cable must be connected and the board powered up.

    Graham
  • GumbaGumba Posts: 14
    edited 2010-02-20 20:23
    Graham Stabler said...
    Like all other propeller based platforms you have two options, press F10 and it will load the program in to the propeller's memory or press F11 and it will load the code into the propeller's memory and the EEPROM which will store the program so it loads every time the propeller powers up.

    You want to press F11, of course the usb cable must be connected and the board powered up.

    Graham
    Thanks.·Got it uploaded.· no change on servo response, sad to say.·
  • hover1hover1 Posts: 1,929
    edited 2010-02-20 20:54
    Firmware doesn't look like it has changed. Still 1.0. Have you tried my idea of connecting another servo supply to the green terminals? Maybe a 7.2 volt RC battery, or you said you had a 6 volt lantern battery.

    Jim
    Gumba said...
    Graham Stabler said...
    Like all other propeller based platforms you have two options, press F10 and it will load the program in to the propeller's memory or press F11 and it will load the code into the propeller's memory and the EEPROM which will store the program so it loads every time the propeller powers up.

    You want to press F11, of course the usb cable must be connected and the board powered up.

    Graham
    Thanks.·Got it uploaded.· no change on servo response, sad to say.
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2010-02-20 21:04
    No great surprise there it was obviously not software if it worked with smaller servos.

    Here is a test that I think will prove something, attach one of your small servos that works and one of the large servos that does not both at the same time.

    If the small one works and the large doesn't then it is probably voltage level changing chips causing the problem. If neither work then most probably is is a supply problem, the larger servo putting noise on the line or dropping the voltage. In which case try an alternative supply.

    Cheers,

    Graham
  • GumbaGumba Posts: 14
    edited 2010-02-21 00:13
    Graham, you're right about the software--I should have known better. hover1, THANKS!!! Your resistor trick worked. Adding a 10k resistor to the signal wire did it. now.....what's next?

    Obviously the board needs some modifications. I'll check back to see what happens when you get the plug in board (from Parallax, I assume?). Maybe this is something they'll ship to others having a similar problem.
  • hover1hover1 Posts: 1,929
    edited 2010-02-21 01:20
    Gumba,

    Sorry for the confusion, but I had some boards made myself, they do not come from Parallax. This is just to get me through a project that I have right now.

    I think the whole resistor thing is just a bandaid right now until we get some some specs from Parallax as to what the output cababilities of the translators are, ie loads, impeadence, etc. It may be noise which has breen brought up before, and the resistor suppreses it. I'm not sure.

    I'd be happy to help Parallax try and sort this out. I have a few animitronics projects based on this one board alone.

    Jim
    Gumba said...
    Graham, you're right about the software--I should have known better. hover1, THANKS!!! Your resistor trick worked. Adding a 10k resistor to the signal wire did it. now.....what's next?

    Obviously the board needs some modifications. I'll check back to see what happens when you get the plug in board (from Parallax, I assume?). Maybe this is something they'll ship to others having a similar problem.
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2010-02-21 01:35
    I don't understand why they chose to put bidirectional translators on the board as servos are not going to be sending anything back to the propeller, I suppose it was in an effort to make it general purpose. I'm sure it worked on all the servos they tried but on reading the input impedance requirements for the translators it is no surprise there have been problems.

    A difficult situation for them.

    Graham
  • hover1hover1 Posts: 1,929
    edited 2010-02-21 01:54
    Graham,

    I think the ability to be bidirectional was going to turn the board into something by far more usefull than the old board. And it is. I use it to input PIR data to trigger servo actions. This saves me from having a·BOE for input and the PSC for output. It's a grand idea that I'm sure will be worked out by Parallax. (I know it could all be done on a Proto Board, but I need the small size).

    I'm sure·if they spec'd it to be used only with the servos that they carry that would have precluded many sales. The old servo boards worked with many servos, but personally, I only started working with Digitals Servos on the new board, and that is when I started having problems.

    Jim
    Graham Stabler said...
    I don't understand why they chose to put bidirectional translators on the board as servos are not going to be sending anything back to the propeller, I suppose it was in an effort to make it general purpose. I'm sure it worked on all the servos they tried but on reading the input impedance requirements for the translators it is no surprise there have been problems.

    A difficult situation for them.

    Graham
    Post Edited (hover1) : 2/21/2010 1:59:53 AM GMT
  • Graham StablerGraham Stabler Posts: 2,510
    edited 2010-02-21 12:59
    Series resistors alone would have made it more capable then you could interface with 3.3 or 5v logic but I guess it doesn't seem very professional.

    Graham
  • hover1hover1 Posts: 1,929
    edited 2010-02-21 13:44
    That's the route I'm going now. First make a Protoboard Nano, (non USB), relocate programming header, relocate 3.3 regulator, install resistor pack(s), install 3-pin headers.

    Initial price is $15.00 cheaper than the PSC, and I added $2.00 worth of components for·4-input/4-output version. A bandsaw and beltsander makes quick work of modifing the Proto Board. Less than 5 minutes.

    Jim


    Graham Stabler said...
    Series resistors alone would have made it more capable then you could interface with 3.3 or 5v logic but I guess it doesn't seem very professional.

    Graham
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