I have an L6 arm that is attached to a large board, so the base is quite solid. However, when I start it up, e.g. All=1500, the arm jumps and sometimes it falls off the base!
Also, when moving it around, it is often very jerky. The strange thing is that it will rotate smoothly say 30 degrees to the left, but if I then tell it to rotate 30 degrees to the right it jerks all the way!
I’ve read posts in this forum talking about power problems, but I am not sure if that is it. I do have VS=VL but I have a 6V 2Amp supply. Is it still possible that I need a separate 9V supply for the logic? It does not seem that the PIC is resetting because the arm continues to move and does not “slump”.
Any suggestions would be most welcome because this is really annoying. The jerkiness makes the arm wave around and with the springs attached and the arm almost fully extended it seems to be even worse because it gets some sort of harmonic going and constantly jitters from side to side. It keeps knocking over the things I want to pick up!
Edit 1: I realised that there is an adapter plug included in the kit for a 9V battery, so I took off the VS=VL jumper and plugged in a battery. That gets rid of the annoying jump when the power is turned on, but it did not solve my other problems with the “stuttering” movements. So it looks like the problem is not the power.
I also noticed that the “turntable” of the base is not making contact with all of the roller bearing. However, no matter how hard I push it down, it still will not sit flush. Maybe is is a little warped?
If the servos aren’t powerful enough to handle the load, the motion will seem very jerky. I don’t know if that is your case or not though. Would you say the servos are actually hesitating and causing the jerkiness or are they operating normally but the movement is jerky?
Jitter can be caused from not enough power but since you said it was smooth in one direction and not the other, I don’t know. Sometimes when servos are moved at a very slow speed you can get jitter. What happens when the servos are commanded to move a little faster? Do you still get the same jitter?
Another thing you can try is to swap out the rotate servo with one of the arm servos and see if it smoothes out the rotation. If it does, then perhaps the rotate servo has an issue.
Thanks for the suggestions guys. All of the servos seem to be jerky, not just the base servo. It is strange however that the base is directional – it is always worse when turning right.
Yes, I do think it has something to do with the speed. My problem is how to speed it up without creating other problems. If it moves too fast, it tends to topple over.
When the arm is fully extended, it spontaneously starts oscillating from side to side and/or bouncing up and down. I think this is aggrevated by the springs. If it is holding something, the extra weight causes the arm to bounce up and down and eventually it pulls the base off the servo hub. I suppose I could glue it on, but I really want to leave that as a last resort.
I am a little disappointed in the L6 because it is not as robust as I had hoped. I am only using it for educational purposes, but still …
You are saying that you didn’t install the servo horn screw into the base ratate servo? That’s one of your problems…
There are many things in the serial control system that can cause jerkyness. We need to know all of the details of your setup in order to provide usefull help. PC make and model, OS and version, serial or usb to serial cable (make and model) if used.
If we can’t sort it out with this information. there is a new version of RIOS coming out very soon. It has several new features to work around slow serial ports. Hold tight, help is on the way.
Doh! Amateur arm builder problem! Thanks for the tip Jim, you nailed it in one. I missed one line in the instructions where it says to install the screw. The arm now rotates smoothly in both directions, and of course it can’t fall off.
When I took the arm off the base, I also discovered that the bottom of the upper arm had been rubbing. My guess is that the uprights that the servo attaches to are not vertical. However, I filed a little bit off the bottom and now I can just see daylight through there. The other side of the arm has plently of clearance. Dunno why.
There is still some jerkiness in the movement of the shoulder and elbow, but I have increased the speed about 3 times what it was and it is better. The spring seems to contribute to the elbow’s problem, but I prefer to have the spring on because the arm does not slump when you turn the power off and it is close to All=1500 when you turn it on.
Thank you to everyone. This little newbie is about to start some serious playing with his new arm
Mistakes are an important part of the learning process because later on down the road when a similar problem repeats, you know where to look and what to check.
Thanks guys. I have to say that your supportive comments have been great. It is in stark contrast to some of the responses I have received on another robot manufacturer’s forum.
