Specification:
| Type: |
|
| Power: |
- Panasonic BP-24221 Solar Panel
- Type 1 solar engine using FLED in series with diode for trigger level
- 16V, 4700µF capacitor
- Canon motor, 5/1 gear drive
- Perfboard SE construction
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| Chassis: |
- 3 wheel - 2 gear driven in rear,1 free rolling
(cassette tension roller) in front
- jumbo paper clip and brass tubing frame
(soldered), fuse holder motor bracket (epoxied to
frame)
|
| Dimensions: |
- 75x40x42mm (width is actually 48mm including the
drive gear)
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| Cost: |
|
Construction Details:
Building on my experience with my first
solar roller I started designing this one with a focus on
balance and stability. I built the frame using a jumbo paperclip
(I got this idea off the web, but I can't remember the page to
give credit) and brass tubing. (I bought an assorted pack of
brass tubing trimmings from the local hobby shop for $3.50.) I
decided to use two drive wheels on a single axle (gears from a
thermal printer mechanism - local surplus shop $2.50) giving a
ratio of 5/1 from my motor. This greatly improved the torque
performance and let me mount the motor in-between the wheels. The
motor is a Canon Seiki (origin unknown) from the local surplus
shop ($3.00).
I attached the motor bracket (fuse clip) to the frame using
epoxy, using the gears themselves for alignment. I placed it so
the motor weight was slightly forward of the drive wheel axle.
The front wheel is a pinch roller with a brass tube axle that the
paperclip frame fit into. It took a bit of playing to get the
front wheel aligned so the roller would go straight.
The solar engine/capacitor/solar panel assembly was attached
to the frame using a tie wrap. This makes it easy to change out
the solar engine assembly for experimentation.
|
 This roller looks much nicer than my
first. It actually looks planned ;-) It is very stable,
and quite strong. The actual frame geometry was a trade
off - I wanted the frame wider (the motor barely fits
between the gear/wheels) but the tubing I had for the
axle was the limiting factor.
 This side view shows the assembly. The
capacitor/solar engine/solar panel assembly is far enough
forward to let the motor slip out without removing the
SE. The motor/drive axle geometry can be seen quite
clearly. The 5/1 ratio gives 1 turn of the drive wheel
for 5 turns of the motor. The roller travels 1m in under
2 minutes under a hazy sun.
 This top view shows how all the
components fitting within the triangle formed by the
three wheels (contact points) leads to stability. The
size of the SE can also be seen (or not seen) under the
solar panel.
 This shows the bare frame separate from
the drive assembly. It was simple to snip the tiewrap
holding the capacitor to the frame and snap out the
motor.
|
Lessons Learned:
- Don't limit the methods of attaching parts! I used solder
for light metal components, but had to use epoxy for the
fuse clip (I couldn't solder to it, and I had nothing to
bolt it to). I was going to use epoxy to attach the
capacitor to the frame, but it seemed too permanent. I
then thought of rubber bands, but while digging for those
found some tie wraps.
- Form follows function (again)! Building this made it very
evident how important balance and center of gravity were
to maintain.
- Design in modules! Building this in modules simplified
the overall assembly. I was built the frame first and was
able to get it balanced and rolling straight by letting
it roll down a slope and re-adjusting the free wheel. I
can also experiment with different solar engines using
the same motor/frame.
- Don't prejudge! I originally planed this to travel with
the single wheel at the front. I found after playing with
it that traveling with the single wheel at the rear was
better for two reasons. 1) The roller would track
straighter. 2) The motor torque would almost lift the
front end when traveling roller forward - reversing the
direction caused the motor torque to push the roller down
for better performance.
(Originally Written May 1998)
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