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Topic: Servo SG90 - No Stops - But still rotating 180° - Error in design? Why? (Read 180 times) previous topic - next topic

Payhaa

Hello,

I've ordered a bunch of servos SG90 on amazon and am confused.
The servos have no stops, I can manually turn them 360.

But then it will behave like regular servos if I use a code with arduino, like the sweep. It will go to a zero position which is always the same, and go to 180° if I ask him to. I cannot order it go further.

If it was only that I could say "oh ok, too bad for the stops, but hey, no harm". But there is a big problem.
If I move it manually between -1° to -60°, and then ask him with arduino to go to 0°, it will travel the shortest way. But if I put him manually past the -60° limit, let's say -70°, then when I'll ask him with arduino to go to 0°, it will travel the longest way (so 290° travel).


https://ibb.co/kgtMS0C (the image won't show in the post for some reasons)

So my question: Is it a problem of construction, like an oversight, or was it purposedly and for some unknown reasons to me designed without stops?

Thanks for your help.

slipstick

I think a more interesting question is why are you manually turning a servo into positions where you know it is not intended to go? Manually forcing servos like that is almost guaranteed to damage the gears.

Quite a few servos do not have physical stops. They're not generally needed if the servos are used correctly.

Steve

Payhaa

Hello Steve, you're tone is awfully patronizing. I don't know if you wanted to answer or just needed your daily dose of insulting someone. But I'll deal with it, I'm on internet.

Stops are here for a reason. And if there are not, you'll design mechanical stops in the frame of your robot. Because in robotics you protect your robots from the not intended positions, which might still happen for some reasons.
Also, when you attach your servo to a mechanical device you'd like to attach it sometimes so it starts at zero. You go to the stop and you attach the moving part of your servo.
Or sometimes you want the maximum width for your mechanical device so you check where are the stops of your servo to attach it accordingly.
And you don't want to have to command your servo into its zero position so you can attach it correctly to your robot. At least for the common robotic projects using SG90...

slipstick

Running a servo to a mechanical stop under power is stalling it. That has never been a good idea. If you want a zero position for your servo you power it up and send it to 0. At least that's how I've used servos for the last 30-odd years. In that time I've also repaired quite a few servos for people who though it a good idea to manually
wind them about or to keep driving them past a mechanical stop.

Obviously you work differently. I hope your servos continue to work too.

I can't actually remember if genuine SG90s have mechanical stops but there are so many SG90 clones and fakes out there that it hardly matters.

Steve

jremington

Quote
Hello Steve, you're tone is awfully patronizing.
No, it wasn't. Steve politely pointed out that you were abusing the servo.
No PM's please.

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