meArm oscillating

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GastonLagaffe
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meArm oscillating

Postby GastonLagaffe » Sun May 18, 2014 6:43 pm

Salut,

first of all: the meArm is a great product. The assembly worked although my clumsy fingers were more in the way than helpful.
However, I have an issue with the arm: The base servo holding the entire arm and rotating it around the z-axis starts to oscillate as soon as I move the arm around that axis. It seems like the servo moves to a certain position but the arm overruns. Then the servo compensates and the arm underruns. The arm starts to oscillate at about 1Hz. Tipping the arm with the finger calms the oscillation down.
The servo looks too weak to me and the arm does not appear to be tightly fixed. I have ordered a micro servo with metal gear to check if a more solid base will fix the problem. The other solution I can imagine would be to add pads that glide between base and waist to support the nutation of the arm. If all fails, I have to come up with some turntable to carry the arm. I'll keep you posted.
I would like to know if I am the only one with that problem.

Ciao, Mathias

phenoptix
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JoinedCOLON Sat Apr 17, 2010 11:25 am

Re: meArm oscillating

Postby phenoptix » Mon May 19, 2014 8:03 pm

Salut Mathias!
Welcome to the forum. Thanks very much for the feedback. It's the sort of problem I've seen at the end of the range of movement but not mid range. Have you attached the servo horn on the base to the servo with one of the servo screws? Seem to remember funny movement on the V0.1 without that screw.
Let me know how you get on!

GastonLagaffe
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JoinedCOLON Fri May 09, 2014 6:45 pm

Re: meArm oscillating

Postby GastonLagaffe » Tue May 20, 2014 10:47 am

Salut,

I have fixed the arm on the servo head using the screw but it still appears pretty unstable. I am thinking abut replacing the servo by a step motor if the metal grea servo fails as well.

Ciao, Mathias

GastonLagaffe
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JoinedCOLON Fri May 09, 2014 6:45 pm

Re: meArm oscillating

Postby GastonLagaffe » Sat May 24, 2014 5:07 pm

Salut,

I have tried to use a metal gear servo of the micro size and detected that that size is not standardized :o . So I first replaced the base servo with another one I have at home (they are pretty inexpensive so I always have some to play with) and the oscillation is gone now. But the replaced servo can still be used for the other three joints.
I then tried the arm on the metal gear servo and using this servo is significantly better. But it requires a change of the waist plate to hold the bigger servo horn and the base plate to hold the bigger servo. However, consider this my suggestion for version 0.4: include a metal gear servo to carry the weight of the arm. They are only marginally more expensive than the standard servo used.
I would also consider to move the arm on to a step motor, perhaps as a "pro" version

Anyway - I start to really like this arm. So I will get me two additional sets to do further testing. In September there is a maker day in Basel and I want to use this arm for a workshop I am heading there.
Ciao, Mathias

theawesomerabbit
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JoinedCOLON Sat Jun 07, 2014 1:43 pm

Re: meArm oscillating

Postby theawesomerabbit » Sat Jun 07, 2014 1:46 pm

are there any instruction for the mearm i am struggling to find them

GastonLagaffe
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JoinedCOLON Fri May 09, 2014 6:45 pm

Re: meArm oscillating

Postby GastonLagaffe » Sat Jun 07, 2014 6:41 pm

Salut,

I followed the instructables guide and it worked nicely for me : http://www.instructables.com/id/MeArm-B ... /?ALLSTEPS

Ciao, Mathias

stozk
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Re: meArm oscillating

Postby stozk » Wed Apr 08, 2015 6:40 pm

I got my MeArm recently and put everything together.

I've connected it to a Espruino to control the servos and was experiencing this oscillating effect.

I've replaced the servos with different sg90 servos I got from Amazon. They seem to be identical, but the oscillating problem is gone now.
They have the exact same dimensions, just the mountings for the axis are a bit different (wider).
Also the resistance when turning them manually by hand to position them is higher, so I guess they have a higher internal mechanical resistance, which fixes the oscillating problem, which has been caused by too fast movements of the parts and the resulting inertia.

screenclene
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Re: meArm oscillating

Postby screenclene » Mon Mar 14, 2016 10:43 am

So, what servos are recommended now to prevent the oscillation?
If you bought servos form somewhere can you provide a link?
What servo model comes with the MeArm kit?


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