Penguin spasms

Grievousfish

Penguin went together okay and I did make sure that I centered the servos.· However, everytime I switch the power on, the servos twitch and hold to a new position.· If I repeat turning on and off the power, the servos will twitch further and futher until they·reach their end limits.

Is anyone else' penguin spasming like this?· I have other servo bots and some times the servos move immediately after the power is applied but if they do, they usually return to center position.·Also, I was wondering whether anyone has tried adding on a PING sensor.

Here's a nitpicky comment for Parallax's marketing department - penguins are native to Antartica.··If you are going to make a tie between the compass·and migration instinct it would be better to emphasize moving south instead of north.
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Mike Green

1) What program have you put in your penguin after centering the servos?

2) Are your batteries ok?

3) Have you tried some of the test programs that come with it?

Grievousfish

1 & 3. I have used all of the test and calibration programs except for the compass calibration programs and the migrate north program. Calibrating the servos has appeared to have cleared up the tendency for the servos to progressively rotate wth repeated on/off switches. Right now I have the program in where it wanders around using the IR sensors. However, there is still quite a pronounced jump of the servos when the power is turned on to the point I fear the poor bot will flip onto its side if I don't have a firm hold on it.
2. I have not metered the batteries but I have only used them for about an hour.

I have noticed that my penguin tends to waddle to the left. I have rechecked the lengths of my rods and they appear to be the correct length. When both servos are in the center position, should both feet be flat on the table?

The manual doesn't really describe what the gait mechanics of the penguin should look like. During stride, should only the lateral edge of the feet be in contact with the table and then the ankle rotate during mid-stride so that the foot is flat?

Post Edited (Grievousfish) : 8/19/2007 4:31:48 PM GMT

Mike Green

When the Penguin is first powered up, it doesn't remember were the servos were when it was turned off. It initializes them to a known position which is what causes the rapid movement when it's turned on.

My Penguin tends to waddle in one direction too (also left). I haven't figured out why yet. When the servos are in center position, my Penguin is upright with both feet flat on the table.

My Penguin walks with the feet flat on the table. It leans to one side then the other as it walks in order to keep its weight over the "planted" foot as it moves the other foot forward.

Chris Savage

Remember that the servo will twitch when the power is turned on regardless of the current position. This has nothing to do with the Penguin or its control board. This is simply how servos work. Now, that said, if your program immediately starts sending servo pulses (for example to center), then the servos should almost immediately center. If, however, your program isn’t sending pulses then wherever the servos end up after the power on twitch is where they will likely stay. Take care.

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Chris Savage
Parallax Tech Support

N-2-STUFF

my penguin also wander off to the left check the leg & foot bolts to make sure they are not to tight or binding.
mine had only one bolt a little to tight. now he walks strait.

scott

Grievousfish

Tonight the poor little guy spasmed so hard when I turned him on that the PING sensor was nearly thrown off! Note: the PING sensor does not seem to fit very securely. If I have centered the servos and calibrated the servos, I don't understand why I should get such an extreme spasmodic twitch. I have other walkers and I have never seen the servos spasm like this.

Mike - your penguin's feet stay flat during the entire stride? Hmm... I guess I should recheck the length of the rods because the only time my penguin's feet are flat are during mid-stride. The medial side of the foot is definitely raised during forward and rearward swing phases so that only the lateral edge is in contact with the table top.

BTW - I really do like my penguin! It is a great little bot.

Chris Savage

The servos used in the Penguin are micro servos. These servos twitch at power on just like any other standard analog R/C servo. I think based on the size of the Penguin and servos; proportionally they’re twitching roughly the same. Unfortunately there’s nothing that can be done about the twitch. It is the nature of the servo when being powered on.

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Chris Savage
Parallax Tech Support

Grievousfish

Hmmm - maybe it is just the weight difference between the penguin and my other walkers that magnifies the twitch. Still slightly alarming. Poor little guy. Maybe I will just have to name him Spaz.

Chris - will the wobbling of the PING sensor affect its operation? I was surprised how loose the fit is.

Chris Savage

I think there may be a slight variance in the SIP sockets used on the board. I can't help but wonder if the soldering (reflow) process affects it some. In any case a customer once posted a picture of his PING))) attached to the Penguin using a rubber band which I think wrapped around the PING))) and under the top PCB. That may be an option if your socket seems loose. Take care.

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Chris Savage
Parallax Tech Support

Humanoido

I'm sure that was my picture with the rubber band. My nickel Penguin robot has been traveling a lot lately and the PING))) sensor in its socket is delicate. It plugs into a three pin sip socket, with only three tiny solder islands to hold it. So it's kind of fragile, and the islands pulled up on my Penguin board. That's when I introduced the rubber band. Since the photo shown here was taken, I switched to a thinner black rubber band. It blends in more and doesn't cover up the Parallax logo.

The important thing to remember is adjust the rubber band so the retaining pressure is exerted directly down on the Ping))) board into the socket. That prevents it from tilting and bending the socket.

humanoido