value, branch to various routines. The values sent by the
MagicCar app are shown in Figure 8 and demonstrated at
Here are my observations about using this app:
1) Fine steering control using the touchpad is possible,
but difficult since you don’t get any touch feedback.
Typically, you’re watching the robot, driving it around, and
the robot’s direction/response is the only feedback you get.
It’s easy to “lose your place” on the touchpad.
Just using your phone/tablet (no robot), move your
finger while watching the speed/direction readout and you
can see how a very small motion makes a huge difference
in the values — especially near the center. It’s easiest to just
look for the eight extreme values (forward, reverse, left,
right, and the four diagonals) since the intermediate values
are somewhat arbitrary.
2) There’s a bigger dead band (center off zone) when
using the tilt sensor. This is necessary since your perception
and orientation of the “off zone” is arbitrary. The center off
orientation is zeroed when tilt mode is engaged. I find it
helpful to lay the phone flat on a tabletop for the OFF
3) Steering and direction data is sent as a continuous
stream (see #4), whereas the four pushbuttons (D, A, G, U)
send a single value per touch (click feedback heard from
4) There’s a bug in the touchscreen (not tilt sensor)
when sending Bluetooth data. The data stream is
continuous as long as your finger is moving, but sometimes
when your finger stops, the data slows down and stops.
When you remove your finger, the value should (but
sometimes doesn’t) automatically return to zero. Depending
on how you write your code, this may
be a factor. The speed/direction
displayed on the app screen is always
correct, but the Bluetooth data has
this glitch. This is Beta software, after
all. I would suggest this workaround:
If driving by using these BT values,
plan to use one of the D, A, G, U keys
to send a zero to stop the robot.
Repeating, the tilt app does not have
this glitch and may be preferable to
That’s a wrap for this column.
Thanks for your question! I sure had
fun hacking and experimenting. I
hope you enjoyed following along and
learned something. Maybe you’ll
decide to get one of these $12 robots
for yourself and have some fun. I
highly recommend it!
As always, please feel free to
share your thoughts, ideas, and
questions with me via email at email@example.com.
SERVO 08.2017 13
Design New Ideas
Cut Real Metal
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