Can I program Scribbler as a
Lots of newbie questions about Scribbler:
I have a Scribbler that I'm trying to get to mimick a LOGO "Turtle".· That is, I want to give it commands to "go forward 1 unit" and "turn 45 degrees"·--so it can "draw" instead of just "scribble".·
I've been programming for years, but I'm just a "newbie" at robots.· Translating from pixels on a screen to a real robot pen on paper is proving to be extremely difficult using only motor speed and time.·
1. When trying to calibrate the two motors to the same speed, I'm finding that they don't even behave the same on two successive runs (possibly slipping on my laminate floors)!
2. And when I stop the motors, one wheel seems to·keep turning·a bit longer than the other, which makes it difficult to program accurate turns.· I even reversed the order of the stop commands but it had no noticeable effect.
3. Are there more sophisticated techniques I could employ?
4. Would I have better control with a BoeBot?·
(Considering a 90 degree turn requires only about 180 degrees wheel rotation, it's not clear that even the digital encoders would significantly improve turning accuracy, if they only provide accuracy to about 22 degrees.··
5. Is it possible to get greater accuracy from the encoders? or some other device?
Of course, a BoeBot with equivalent sensors plus digital encoders for the wheels would cost about twice as much as a Scribbler--would it be worth it?)
BTW, it seems computing wheel rotation angle for turns would be greatly simplified if the axle length were in a simple ratio to the wheel diameter.· As it is, on the Scribbler it is nearly, but not exactly, 2:1 (14.7:8 cm).· But why not "exactly"?·
6. Is it possible to make the ratio exact on the BoeBot, e.g. by changing axle length or effective wheel diameter?
And another thing: Scribbler has a pen but·no penup/pendown.
Guess that would take another servo, or at least a solenoid.·
7. Is there something like a penlifter for the BoeBot (or Scribbler)?·
8. Or even a way to get a hole in the middle of the BoeBot (the optimal position) for a pen?
Any help or suggestions for further reading would be appreciated.
I have a Scribbler that I'm trying to get to mimick a LOGO "Turtle".· That is, I want to give it commands to "go forward 1 unit" and "turn 45 degrees"·--so it can "draw" instead of just "scribble".·
I've been programming for years, but I'm just a "newbie" at robots.· Translating from pixels on a screen to a real robot pen on paper is proving to be extremely difficult using only motor speed and time.·
1. When trying to calibrate the two motors to the same speed, I'm finding that they don't even behave the same on two successive runs (possibly slipping on my laminate floors)!
2. And when I stop the motors, one wheel seems to·keep turning·a bit longer than the other, which makes it difficult to program accurate turns.· I even reversed the order of the stop commands but it had no noticeable effect.
3. Are there more sophisticated techniques I could employ?
4. Would I have better control with a BoeBot?·
(Considering a 90 degree turn requires only about 180 degrees wheel rotation, it's not clear that even the digital encoders would significantly improve turning accuracy, if they only provide accuracy to about 22 degrees.··
5. Is it possible to get greater accuracy from the encoders? or some other device?
Of course, a BoeBot with equivalent sensors plus digital encoders for the wheels would cost about twice as much as a Scribbler--would it be worth it?)
BTW, it seems computing wheel rotation angle for turns would be greatly simplified if the axle length were in a simple ratio to the wheel diameter.· As it is, on the Scribbler it is nearly, but not exactly, 2:1 (14.7:8 cm).· But why not "exactly"?·
6. Is it possible to make the ratio exact on the BoeBot, e.g. by changing axle length or effective wheel diameter?
And another thing: Scribbler has a pen but·no penup/pendown.
Guess that would take another servo, or at least a solenoid.·
7. Is there something like a penlifter for the BoeBot (or Scribbler)?·
8. Or even a way to get a hole in the middle of the BoeBot (the optimal position) for a pen?
Any help or suggestions for further reading would be appreciated.
Comments
Don't know if you have this either. It is from the Scribbler Download section on the Parallax site
http://www.parallax.com/dl/docs/prod/robo/scribbler/SPPG-WritingPrograms-v1.2.pdf
There is a lot of good information in the Online help for the GUI software (including the callibration issue). I will put a link to a recent post about this issue below.
About the pen up and pen down. I have never seen anything about this. Sound like a neat idea. There is a hackers port inside the Scribbler. This might allow a fairly easy way to work on this problem.
Hope this helps.
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Whit+
"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
Post Edited (Whit) : 6/22/2007 6:59:09 PM GMT
http://forums.parallax.com/showthread.php?p=634274
One of the manuals listed above said this:
I thought I had read somewhere about the motors breaking in over time.
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Whit+
"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
Post Edited (Whit) : 6/22/2007 7:15:35 PM GMT
You might check out the program code shown and also·attached below. It is from the Hacker's Hints Download·section of the Scribbler website. You could load and run·it and see how your Scribbler responds.
' Scribbler Robot Demonstration Code ' Motors.bs2 ' Drives forward for 2 seconds, turns right for 1 second ' using a duration command, and then pauses for an extra second, ' in a continuous loop ' (C) Parallax Inc. 2005 ' {$STAMP BS2} ' {$PBASIC 2.5} ' I/O Declarations MotorRight PIN 12 MotorLeft PIN 13 ' I/O Initialization LOW MotorRight LOW MotorLeft DO ' Drive forward at half speed PULSOUT MotorRight, 2500 PULSOUT MotorLeft, 2500 ' Wait 2 seconds PAUSE 2000 ' Turn right for 1 second PULSOUT MotorRight, 1500 PAUSE 1 PULSOUT MotorRight, 1400 PULSOUT MotorLeft, 2500 PAUSE 1 PULSOUT MotorLeft, 1400 ' Pause for the 1 second turn and an extra second PAUSE 2000 LOOP▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Whit+
"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
Post Edited (Whit) : 6/22/2007 2:04:17 PM GMT
I notice this seems to be sending two pulses, 1ms apart, to each servo (driver?);
I didn't notice anything about that in the Scribbler PBASIC guide·or even in the BoeBot Robotics doc.
But I also understand that the Scribbler has a separate processor for the servos so you don't need to repeat the speed pulse every 20ms.· Is the 1400 a second operand for duration?· If so, how does it·get "1 sec" from 1400?
JoeA
Don't have time for a complete answer and will be away for about a week at camp. See attached file (or ·http://www.parallax.com/dl/docs/prod/robo/scribbler/SPPG-WritingPrograms-v1.2.pdf) - espcially page 15. The PAUSE sets time. PULSOUT sets motor (left or right)·speed (forward or backward). Hope this helps. I'll see what you're up to when I get back. Good luck!
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Whit+
"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
Post Edited (Whit) : 6/23/2007 4:26:50 AM GMT