Bot 08M
@ December 27, 2008
- Actuators / output devices: 4x hextronic HXT900 servos. 2 modified for continuous rotation.
- Control method: autonomous
- CPU: picaxe 08M
- Power source: 6x AAA NiMh - 7.2V
- Programming language: Picaxe basic
- Sensors / input devices: Maxbotix EZ1
- Target environment: Indoors - Carpet / tiles
| Attachment | Size |
|---|---|
| Bot_08M.bas | 2.37 KB |
| LV-MaxSonar-EZ1-Datasheet.pdf | 405.49 KB |
| Bot_08M_sane.bas | 2.58 KB |
This is an experiment to see what sort of robot can be made with a cheap picaxe08M. It is also the first time I've actually used my "reusable robot base" as a robot rather than a power supply / test bed. The program (see attachments) is very basic and only uses about 2/3rds of the 08M's memory so there is reasonable room for improvements.
One curious feature of this robot is that it doesn't always do what it is supposed to, sometimes it will go towards an obstacle instead of away from it as though it wants to examine the object. I haven't bothered trying to correct this apparent fault as it makes the robot appear to be curious about things.
To make the most of the picaxe08M's 5 pins I'm using the maxbotix sonars pulsewidth output since pin 3 is input only but doesn't read analog inputs.
I've been a bit slack (or is that creative) with power to the servos. I really should power them straight from the batteries with a couple of diodes in series to drop the voltage down to 6V. Instead they are running off of the 5V supply which has a 0.047F (47000uF) 5.5V super cap on it to absorb the spikes. This seems to work quit well with no servo jitter.
Click on image for a closer view.
Sunday 28th December 2008
Found the fault in my code, the turn left and turn right subroutines were turning in the opposite direction (thats what happens when you write code late at night). The new sane code (see attachments) is far more predictable but also less interesting as you can see in the second video. I've also made him backup more often to avoid getting stuck so much (as suggested by Frits).
07-09-2009
My smallest robot is now joining the list of LMR robots to be produced by DAGU. Although he has been re-designed a bit with some new features and a new name. Mr. General (general purpose) is just that, with the breadboard allowing easy use of any microcontroller.
Mr. General combines the new pan/tilt version of the sensor bracket designed here on LMR with my IR obstacle detectors and IR tracking system.
@ Sat, 2010-02-20 14:07
BOT 08M - Nice buddy - thinking about something similar myself!!
Hi, Just wanted to say that you have inspired me to create something similar! Beatiful work you have done using the little 08M :)
I was thinking of using the 08M starter kit for amateurs like myself :) With the 08M starter kit you loose one of the in/out pins for programming - so the unit will only have control of 3 servo's - this shouldn't be a problem if using the Tamiya tank/wheel set as small objects and cables shouldn't impede the robot's movement much.
I've managed to find an Australian supplier for cheap continuous rotation servo's and a trusty SR05 utralsonic range finder (should arrive next week) - so hopefully I'll get a chance to start working on the robot this week!!!
Just have a question or three (hope u dont mind me asking), I will be using a 6xAA nimh pack (7.2v), it looks like you are using a voltage regulator (7805?!?!) to regulate the power supply to the picaxe to 5v - is this correct? It also looks like you are using the same power supply to power the servo's but instead of the voltage regulator you are using a 4.7v capacitor - is this correct too?
P.S. It would be kinda cool to have a self charging version of your robot with solar cells (replace with an LDR or LDR array) - however a limitation could be program space for extra logic / light seeking routines.
P.S. Apologies to everyone for the lengthy post!
@ Sun, 2010-02-21 09:57
Voltage regulation
I used a LM2940CT +5V low drop out regulator from Jaycar. You can get them a lot cheaper from Futurlec but you need to wait a month or so for the postage :(
I explained in the post that it was all running from the 5V regulator.
Have a look at my tip/walkthrough on voltage regulation here: http://letsmakerobots.com/node/3880
Memory limitations are probably the biggest problem with the 08M, 14M and 20M
@ Sat, 2010-02-20 21:40
I don't now how the starter
@ Wed, 2009-08-12 17:47
Motor driving
HI sir,
nice robot.Can you please share the details of the motor driving circuit you have used.
I'm planning to do a 08M based robot.As I am a total novice to this field I badly need help from pepole like you.
Thank you
@ Thu, 2009-08-13 04:58
G'day Mate
The motors are servos that have been modified for continuous rotation and have their own control circuitry built in. This is important when using the 08M chip because you only need one pin to control the speed and direction of the motor.
You will find many tutorials on this site and on the rest of the net demonstrating how to modify servos. Some shops even sell them modified.
@ Mon, 2008-12-29 11:37
very nice this little bot!
very nice this little bot!
Specially his little and funny eye.. remainds me a peak of a duck, looking for food and always alert :)
And I confess I prefer the first video, where he is more erratic, but at the same time seems more curious, likes to look through things, and likes to wander :)
good job ;)
@ Mon, 2008-12-29 13:49
He does move a bit like a bird looking for a worm.
@ Mon, 2008-12-29 14:26
that is a good idea, hope
that is a good idea, hope you manage it!
on the second video (minute 1:05), while he spins he sends a sonar ping and instead of moving out of the wall he drives backwards into the wall :)
@ Sun, 2008-12-28 21:45
I don't want to think about
@ Sun, 2008-12-28 00:54
Gold Star