At home with just the kids, used the SBrick for a RC micro rover:
It’s very fragile but I’m certain it is possible to make it even smaller and sturdy, just a matter of time and skill.
[actualized on the next day]
A slightly better version witj less friction at the connection between the weels and the micro-motors. Also tried 3 CR2430 lithium batteries to supply 9 Volt. The batteries behave better than expected.
Almost out of nowhere I now have a table robot with great potential for Snap!
[new actualization]
Robot consumption with 3 fresh CR2430 batteries goes from 60 mA (moving forward) to 90 mA (rotating over itself).
I found out that is really easy to use a wiimote with Linux for so as a sequel to my previous ‘Sbrick – remote control with a wireless gamepad‘ I now present you my ‘Controlling the SBrick with a wiimote’ (actually a cheap clone, a N-Play Remote Plus, unfortunately I haven’t found a version with Motion Plus).
The wiimote uses Bluetooth, but doesn’t strictly follow the rules. If we have bluetooth on our PC and want to check if it will work, just press both ‘1’ and ‘2’buttons for it to advertise for a while and then:
$ hcitool -i hci0 scan
Scanning ...
04:02:16:01:1C:E7 Nintendo RVL-CNT-01
It’s not possible to pair with the wiimote but there are tools for that, like cwiid. As I’m going to use python I installed their python library:
$ sudo apt-get install python-cwiid
There are lots of examples so I’ll show only my final result:
And the script I used for the video above:
# apt-get install python-cwiid
import cwiid
from time import sleep
from subprocess import call
from math import log10
# macros for the SBrick
DRIVE_A="gatttool -b 00:07:80:7F:28:E1 -i hci0 --char-write --handle=0x0025 --value=0102"
DRIVE_B="gatttool -b 00:07:80:7F:28:E1 -i hci0 --char-write --handle=0x0025 --value=0103"
COAST_A="gatttool -b 00:07:80:7F:28:E1 -i hci0 --char-write --handle=0x0025 --value=01020000"
COAST_B="gatttool -b 00:07:80:7F:28:E1 -i hci0 --char-write --handle=0x0025 --value=01030000"
BREAK_A="gatttool -b 00:07:80:7F:28:E1 -i hci0 --char-write --handle=0x0025 --value=0002"
BREAK_B="gatttool -b 00:07:80:7F:28:E1 -i hci0 --char-write --handle=0x0025 --value=0003"
# connecting to the wiimote. This allows several attempts
# as first few often fail.
print 'Press 1+2 on your Wiimote now...'
wm = None
i=1
while not wm:
try:
wm=cwiid.Wiimote()
except RuntimeError:
if (i>5):
print("cannot create connection")
quit()
print "Error opening wiimote connection"
print "attempt " + str(i)
i +=1
#set wiimote to report button presses and accelerometer state
wm.rpt_mode = cwiid.RPT_BTN | cwiid.RPT_ACC
#turn on all led and ruble to show connected
wm.led=15
wm.rumble=True
sleep(0.5)
wm.rumble=False
wm.led=0
sleep(1.5)
# roll = accelerometer[0], standby ~125
# pitch = accelerometer[1], standby ~125
while True:
buttons = wm.state['buttons']
#only pay attention when button '1' pressed
if (buttons & cwiid.BTN_1):
roll=(wm.state['acc'][0]-125)
pitch=(wm.state['acc'][1]-125)
if (roll<0):
if (roll<-4):
if (roll<-25):
roll=-100
else:
roll=-50*log10(-4*roll)
else:
roll=0
if (roll>0):
if (roll>4):
if (roll>25):
roll=100
else:
roll=50*log10(4*roll)
else:
roll=0
if (pitch>0):
if (pitch>4):
if (pitch>25):
pitch=100
else:
pitch=50*log10(4*pitch)
else:
pitch=0
if (pitch<0):
if (pitch<-4):
if(pitch<-25):
pitch=-100
else:
pitch=-50*log10(-4*pitch)
else:
pitch=0
if ((pitch<>0)or(roll<>0)):
roll=2.5*roll
pitch=2.5*pitch
if(pitch<>0):
if(roll>0):
# turn right
motor_L=pitch
motor_R=-pitch-roll/2
else:
# turn left
motor_R=-pitch
motor_L=pitch+roll/2
elif(roll<>0):
#just rotate
motor_R=motor_L=roll;
else:
# does nothing
motor_R=motor_L=0
if((motor_R<>0)or(motor_L<>0)):
if(motor_R<0):
duty=str(hex(int(-motor_R)))
command_A=DRIVE_A+"00"+duty[2:]
else:
duty=str(hex(int(motor_R)))
command_A=DRIVE_A+"01"+duty[2:]
if(motor_L<0):
duty=str(hex(int(-motor_L)))
command_B=DRIVE_B+"00"+duty[2:]
else:
duty=str(hex(int(motor_L)))
command_B=DRIVE_B+"01"+duty[2:]
#send motors commands to SBrick
call(command_A, shell=True);
call(command_B, shell=True);
sleep(0.1)
#send COAST commands to SBrick
call(COAST_A, shell=True);
call(COAST_B, shell=True);
else:
# inactive
sleep(0.01)
