basic stamp- servo motors
Hello, I was wondering if someone could tell me, how many servo motors can be run·using I/O·on the basic2 homework board. Also, can power and ground be supplied separately to the servo while using the pulsout signal from the bs2? thanks
Comments
You can certainly supply power separately to the servos. You need to have a common ground connection. A 6V supply is best.
·Will you please explain to me what you mean by "shutdown?" Pardon me for asking something that is doubtless obvious.
--Bill
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You are what you write.
I am loving the Boe and the lessons, but right now, I am struggling to keep the DURATIONS constant in performing things like a simple 1 ft radius right turn, straight driving, and all the other maneuvers. Whats happening is: I will spend several rounds of setting the durations, watching the travel, resetting the durations, and so on until I get it to do exactly what I want it to do. Then I will move on to the next maneuver and perform the same steps. However, when I go back to a previous maneuver that was already fine tuned and try it again, it won't repeat the maneuver anywhere near the way it did before. It seems to me that the battery levels are playing havoc on the repeatability. I say this because I can spend 30 minutes running the Bot back and forth from the computer to the floor executing the same maneuver to fine tune it and it eventually gets achieved. Then after I set the Bot down and work on some programming or something for 20 minutes and go back and try the same maneuver again, it doesn't perform it the same. Is this inherent of the servos? Or, do I need some sort of voltage regulator in the circuit to achieve a steady voltage? I'm talking about the duration argument not being off by 1 or 2, it's goes off by 30 to 40. I calibrate it again to do the task and over and over this keeps happening.
-I centered the servos.
-I attached all mechanical parts precisely as directed by the book.
-I refresh the batteries prior to full depletion. ( I am most of the time running the Boe on what I would say was batteries in mid cycle...not fully charged and not low)
-I test run after test run to fine tune each maneuver until it can repeat it multiple times before I start a new one.
-I am using simple PULSOUT commands with no variables that could be getting mixed up.
counter VAR Word
' Boe-Bot Spin Left
FOR counter = 1 to 24
PULSOUT 13, 850
PULSOUT 12, 850
PAUSE 20
NEXT
This is all each of my maneuvers consist of.
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It's not the size of the dog in the fight, but the size of the fight in the dog.
Look at the wheel position encoder kit for the BoeBot. This allows the BoeBot to track the actual distance moved by each wheel. You will still have problems with wheel slippage on the ground that the encoder won't measure. The only way around that is for the BoeBot to have some kind of absolute position mechanism. You can't use dead reckoning.
www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/80/Default.aspx?txtSearch=wheel+encoder
@Bill Chennault - As I understand it, analog RC servos use the control pulse to turn on the control circuitry that holds the motor in position (probably to save battery power). I'm sure there's an RC delay circuit set for somewhere over 20ms that switches on power to the H-bridge. If no pulses come in, somewhere past 20ms, the motor power is turned off so the servo mechanism won't maintain position. The only thing doing so is the friction of the geartrain. If you use pulses, say 50ms apart, the motor will have a jerky movement and tend to slip because the power is being turned on and off.
Thanks. You pretty much exactly described my problem, which appears to be similar to eiplanner's.
I will play around a bit with the little Parallax "Standard" servo. All I want it to do is move the Ping sensor back and forth and that probably does not have to be highly accurate! If I can't get it to do what I want before long, I will go to Plan B, which is probably three Pings mounted at some more or less optimum angle relative to one another on the front of the machine.
--Bill
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You are what you write.
I'm a little disappointed with the inaccuracy of the servos. I would have liked to be able to perform dead reckoning with the Bot. It sounds like the only way to accomplish it is through the use of sensors, place marks, line following and such. Even then, I fear the movements might be a bit jerky.
I will try the extra battery or maybe even another 4 pack, a separate voltage regulator, some pulse ramping, a stationary on signal to wake up the servos, and anything else I can come up with and I will post back the results.
Thanks for the information.
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It's not the size of the dog in the fight, but the size of the fight in the dog.
" I am a little disappointed with the acceleration of my Yugo. I would have liked to go from 0 to 60 in 3.5 seconds. " [noparse];)[/noparse]
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- Stephen
I am up an unsanitary tributary without any feasible means of propulsion!
or better yet, it sounds like you are saying...
I chose to enter the unsanitary tributary without even considering propulsion.
Page 132 of the "Robotics with the Boe-Bot" refers to dead reckoning as a very popular entry level robotics contest under Activity #3: Calculating Distances. The book also states that you must use trial and error to fine tune your Boe-Bot. After spending at least 12 hours tweaking and tweaking the PULSOUT Durations and still not getting the Bot to make a full 4 ft diameter circle and stopping in the start location, I simply inquired about what I might be doing wrong. Upon finding out that it is not even possible to accomplish this with just the servos, yes, I was disappointed! I wasted a lot of time on something I shouldn't have.
I don't think I was wrong in assuming that the Boe-Bot was an entry level robot that was capable repeating the same movement twice. A small note in the text concerning inaccuracies of servos may have saved me some time. It was like shooting a gun with a warped barrel and wondering why you can't hit the bullseye.
Thanks for sharing...
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It's not the size of the dog in the fight, but the size of the fight in the dog.
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- Stephen
Also, the servos being non precise as they are, may not respond proportionally identical. If you do some testing by timing rotations you can figure out if a correction factor is needed to be applied to one of the servos.
Note that these things will not achieve fine repeatability, however, it may help a bit.
Another thing, as the PULSOUT values change the duration of your loop will change. In pursuit of the best accuracy you need to modify the PAUSE times appropriately:
Rich H
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The Simple Servo Tester, a kit from Gadget Gangster.
Post Edited (W9GFO) : 1/11/2010 8:14:08 PM GMT