Servo responds incorrectly

[sn96]

Mike,

Could you post the code you are using so we can take a peek at it? When you say the servo is moving in the wrong direction I wounder what would happen if you instruct it to move the other way. What happens?

When you move a servo one direction, you must instruct it to move to center or to a new location or it will stay in the last position.

Forgive me if I am asking questions that you are already aware of.

[mwgemini]

I am using the LynxTerm program. I also have tested it with my own code, but the results are the same. Every result I have posted so far has happened with the LynxTerm program. It isn’t a serial communication issue.

Mike

[robotdude]

@MWGemini

These problems were/are: moving in the wrong direction, and locking up in the clockwise direction when given a fast or long move command.

Initially, I was powering both the servos and the logic off a single 6v PSU. Powering the logic off a 9v battery solved the logic reset problem I sometimes had, but the other problems have persisted.

Are you sure you removed the VS=VL jumper? This is required to completely separate the two supplies.

@MWGemini

When you say “real” servo, what exactly do you mean? I have a total of 19 “real” servos, but they are not manufactured by any of the companies you list. While they are physically real, they may not be real by your standards (in terms of quality?). All my servos are manufactured by Blue Bird (which I went with because of higher power, but probably would not have, if they are indeed the problem child here).

Sorry, sorry, sorry… I just mean we need to test your controller with a name brand servo, that’s all. However I do know the Bluebird servos will hold a position, so it’s got to be power supply related.

@MWGemini

I have tested about a dozen different servos at this point, of two different models, and they are all doing the exact same thing. I am going to try to find a better PSU tomorrow and see if that affects the behavior at all.

Mike

PSU = power supply unit? The power supply has to be a regulated DC unit. Some unregulated wall packs have way too much AC riding on the DC to be of any use. And if the supply is not powerful enough it can cause the servo to act eratic even with good pulses coming in. Even analog devices have voltage and current requirements in order to function. If you could throw a volt meter on the bus and watch it while the servos are trying to move that could speak volumes.

[mwgemini]

Yes, the VL=VS1 jumper is off the board. The other two jumpers (VS1=VS2) are installed.

Not sure if the BB count as name brand. The more I work with the them, the less I like them. I should have just ordered from you. Live and learn, I guess.

And yes, PSU is a wall power supply. I think I stole it from an old CD player, but I can’t be sure on that. I had it laying around gathering dust, and so have been using that. I think this is where the problem lies. Andy also holds this opinion. While measuring the voltage at the VS1 terminal, it stayed in the high 5v to low 6v range while idle, and dropped to the mid to high 4v range while moving slowly. When issuing a fast/long move command, it abruptly dropped to the low 2v range (roughly 2.25v) and remained there while the servo was frozen. I tested this several times, with roughly the same results. The voltages were slightly different, but that is to be expected.

So, it looks like the problem lies with the power supply. I’ll definitely be getting a replacement tomorrow, and will post again with results.

Thanks,

Mike

[robotdude]

@MWGemini

While measuring the voltage at the VS1 terminal, it stayed in the high 5v to low 6v range while idle, and dropped to the mid to high 4v range while moving slowly. When issuing a fast/long move command, it abruptly dropped to the low 2v range (roughly 2.25v) and remained there while the servo was frozen.

Oh yeah! Who’s the man?.. (Aparently Andy and I) I am so incredibly happy this problem is finally solved! Nuff messin round, now on to the fun!

[mwgemini]

A HUGE thanks go to Andy, who helped me to build a voltage regulator circuit. Using this, I was able to solve the servo locking up issue. Now my only issue is the direction issue.

I’ve been doing some research on these servos, and it appears that they should be rotating clockwise with longer pulses, the same way that Hitecs do. That is not the case here, and I have not yet heard from the supplier I purchased them from as to whether this is normal. All 19 of my servos do this, however, so I am assuming it is, and may just be a documentation error. Either way, I can easily account for this reversal in software.

Thanks to everyone for helping me troubleshoot these issues. I am now one step closer to finishing construction on the robot.

Mike