Fine Control of Firing Device
Posted on Tuesday 30 October 2012
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This system
should allow the user to move the firing device in small increments after
positioning the robot. An illustration
of the movement can be seen below.
This movement can either be on the x axis or on the y axis, turning the
device horizontally or vertically.
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| FINE CONTROL OF FIRING DEVICE |
Using this
system it will be possible to alter difficulty by limiting range of movement
therefore forcing user to move robot, or speed of movement.
Chosen Design
Most solutions
involved using servos to move the firing device. These servos are often used in
RC cars to move throttle arms and steering position. They usually have low power consumption due
to their portable use, and are small in size. This makes them ideal for our
application. They also tend to be low cost.
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| EXAMPLE OF SMALL, LOW COST SERVO |
Many designs
use two servos, one for the x axis, and one for the y axis.
The y axis
servo is to have the firing device attached to it, with that mechanism mounted
on top of a servo that controls the x axis.
This design will mean that the lower servo does not have to lift the
weight of the second servo and the firing device, just rotate it, meaning it
will require a lower power/torque rating.
The servos can
be controlled with Pulse Width Modulation from an Arduino’s digital output,
giving a faux analogue voltage. This voltage can be fed into the control line
(the other two being power).
Other Options
Suggestion 1
This was to
create a mounting for both the camera and the firing device. This would cause the mounting to be much more
complicated and heavier – requiring heavier, more powerful and more expensive
servos. The advantage would be that the
camera would move with the firing device, helping the user to aim, however it
could become confusing with the robot moving too.
A simpler solution could be to mount the camera behind
the firing mechanism, so the user can see the position of it through the video
feed.
Suggestion 2
Cost could be
cut by having the firing mechanism just move in one direction, so the x or y
axis. This issue with fixing the y axis
is it places the onus on the designer to get the height of the target correct,
as the user cannot adjust this.
Fixing the x
axis is possible, as the user can adjust by moving the robot. It is suggested
that this is used as a fall back if the mounting for the two servos proves too
time consuming. The flexibility that the
two servos give for changing difficulty etc. outweighs the disadvantages of the
complicated mounting.
· Lower (X Axis) servo:
Components
· Lower (X Axis) servo:
o Name: Futaba S3003 – Standard Servo
o Price: £8.70
o Voltage: 4.8V/6V
o Speed: 0.19 sec/60°
o Weight: 37.2g
· Upper (Y Axis) servo:
o Name: Tower Pro Analog Servo
o Price: £1.96
o Voltage: 4.8V/6V
o Speed: 0.12 sec/60°
o Weight: 9g
Lower servo was chosen as standard solid option, with favourable reviews among RC community at (http://www.servodatabase.com/servo/futaba/s3003). Upper servo was chosen due to extremely low cost and weight, if it doesn’t work or is not suitable, not much loss. Also has been used in similar applications (http://vimeo.com/18837811).
