All Servos are shaking

Hexy Questions, Problems and Suggestions
#1

Hello,

i have the problem that all servos are shaking when doing movements. So what I do yet:

When building my Hexi I testet all the servos by sticking them into my RC plane. One of them was a bit louder than the others, so I did not use him. The others all seems to be all right. When i installed everything to test it, I noticed that all the servos are shaking while movement. Also when i only move 1 servo by PoMoCo, the other servos are shaking. If i kill all servos and just move 1 servo by PoMoCo, it also shakes while moving. After ending the moving, nothin shakes. Here is what i tried:

  • I Installed all of it on a windows7 and a xp system
  • I used Servotor32 v2.0 Firmware and Servotor32 v1.7 Firmware
  • I used 4xAA Batteries and tryed it with a power supply - 5V DC 3A 15W

Nothing of it helped. Now I dont know how I can fix this problem.

Greetings, Arcanix

Servo twich when sending serial commands
#2

When doing moves it’s common for there to be some vibration in the servos. If it’s strong enough to cause big movements, there is a problem, but some shaking is normal. At least in my experience.

I’m attributing this to an overly aggressive feedback loop in the servo (not something we can modify).

#3

Hello rpcook,

they shake about 1-2cm to each side. It is definitely to much.

Greetings, Arcanix

#4

When you say 1-2cm, do you mean the end of the foot is swinging that far, as the hip servo swings back and forth?

#5

Hello roboalchemist ,

yes, I do mean the end of the leg shakes about 2cm to the left and 2cm to the right (about 0.8 Inch to every side). I will try to post a video in the next days, never did something like this yet. Someone knows an easy way posting a video in here?

I hope i did discribed it clearly. My english is not good. If you have any further questions or understanding problems, just let me know.

Greetimgs, Arcanix

#6

Hello,

I noticed that when i plug in the USB from my hexi to my computer that 2 new devices appears in my device manager. I marked them red in this picture:

s14.directupload.net/images/130123/7jnqoiib.jpg

Is this ok or could this be an error?

Greetings, Arcanix

#7

Hello,

so I made a video on uploaded it to youtube. In this video i did 2 times a “reset-move” and at the end a “point-move”. It looks really horrible. I really dont know what to do.

youtube.com/watch?v=DNUJ5zyZ … e=youtu.be

Greetings. Arcanix

#8

What are you using for power?

#9

Hello TooManySecrets,

I tried:

4x AA 2100mAH
4x AA 2600mAH
power supply - 5V DC 3A 15W

Always the same problem. See my threads above what I also tried.

Greetings, Arcanix

#10

That power supply is probobly putting out some dirty power and it has to be a 5amp supply at least. Those are not rechargable batterys right?

#11

Hello TooManySecrets,

they are Ni-MH rechargable batteries. I read much in the forum and the tips from the developers. I would not write in this forum untill I tested everything :slight_smile:

Does it look like that the batteries are the problem? I cant belive that because also the 2600mAh did not fix it.

Greetings, Arcanix

#12

4x rechargable batteries is 4.8 V which is on the down limit for a servo, they usualy run best 5-6V.

Try adding another battery into the mix which will make it 6V.

Also read if your batteries are 1.2V each. rechargable ones usually are. The normal alkaline batteries are 1.5V each.

#13

We have tips on this here:
github.com/ArcBotics/Hexy/wiki/Servos

The gist of it is:
Yes, this is normal. When hexy has feet on the ground though, it won’t shake the hip.

[quote=“TooManySecrets”]4x rechargable batteries is 4.8 V which is on the down limit for a servo, they usualy run best 5-6V.

Try adding another battery into the mix which will make it 6V.
[/quote]

We actually recommend 4.8v to make it shake less. You should be using as little voltage as you need to accomplish your task. See the guide.

#14

Mine shakes less at 6V really and mine does not shake when on the stand. It might just be due to dirty power supply. But cant explain why it wont work on his batteries.

edit:

Oh sorry i forgot i upgraded to turningy metal gear ones.

#15

Hello,

I tried it with 5 batterys and killed the 2 servos that hexy is using for the “point-move”. I checked the rest of the servos with my RC plane and they are still ok. Now I put all servos out of the board and only let 1 foot in it. this is the test when i move the scrollbar in PoMoCo.

youtube.com/watch?v=EN6bl8Qf … e=youtu.be

It dont seems to me that this is ok. I will buy tomorrow brand new recharable batteries and try it again. I will report.

Greetings, Arcanix

#16

New batteries will not solve the problem, as the problem is not related to the power supply. It has to do with a large moment arm inertia on the servo. The only way to guarantee the shaking stops is to have the robot walk on the ground, or to use much more expensive servos.

#17

I had a leg that was shaking too, and I suspect that you will find that the hip servo on that leg is looser (in it’s holder) than the other hip servos. When I took apart that hip (top of the leg) and put a piece of folded paper (enough folds to make the servo wedged tightly in place) in place the shaking went away.

I think that the servo starts moving which accelerates the leg, the servo stops at it’s desired position and the leg swings freely for just a bit (due to the looseness of that servo)… and then catches and jerks the servo past that desired stop point. The servo responds by trying to move “back” and the process repeats in reverse. I think that this happening over and over is the cause of that twitch.

Try making sure there is no play between any of the servos and the framing that is holding them, and if there is try shimming them tight?

Hope this helps,
Hunter

#18

Hello CvilleEmbedded,

i also noticed by building the hexy that the servos dont have a perfect fit. so i decided to put some “moosgummi (german name of it” between the servo and the plastic. you can see it here:

s14.directupload.net/images/130125/jdauoca9.jpg

…the green “thing” in the picture". I fitted all the servos with it. so the servos are good be holded in position.

Greetings, arcanix

p.s. looked for a translation of “moosgummi”, didnt found. its like a piece of soft rubber.

#19

Hello,

i have decited to write my own assembler routine and here is my first test:

youtu.be/Q4POfuNJluc

No more shaking and powerful movement is the result. It is based on the 8 bit interrupt timer.

At the end I also starting to love my hexy. Really nice work from the developers! Thanks for the fun I will have with it!

Greetings, Arcanix

#20

Interesting. Just got hexy built, and I notice a good deal of anomalous movement in other servos when controlling ony one with the slider in PoMoCo. There really is no reason I can think of for other servos to jerk about when you are only sending pulses to one. I’ll try some custom Arduino code on the Servotor32 instead of the firmaware and see what transpires.