Approaching this with a full analytic solution is probably pointless. Even
with static/dynamic analysis of the
mass of the panel, the wind, rain, snow, someone leaning on it, pitch of
the craft, etc all add enough
uncertainty that the numbers are near enough irrelevant.
As a first order guess, take the mass of the panel and assume it a point
load on the end of the drive arm
and assume the arm to be horizontal  - all worst case scenarios.

You probably don't want the stepper arrangement to be exactly as you've
sketched it. In this config, the
motor would constantly need to be powered to fight gravity. That motor load
would be a significant portion
of the power from the panel. Running the same motor through a leadscrew or
possibly a worm drive
mechanism would allow the motor to be powered off and the panel remain
stationary.

Also, I probably wouldn't recommend a stepper for this application.
Steppers are great for open-loop
positioning when the motor can be sized significantly above the load to
assure no missed steps or
back-driving. Further, it's a solution I would look at for a ground station
trying to base the position on
emeritus data - not so much a mobile unit unless you want to figure GPS
position as well as roll/pitch/yaw
into the calculations. In your application I would consider two (per axis)
small solar cells or possibly LDRs
set on opposite sides of a baffle. Mount this so it moves with the panel.
Then set the control system to
drive the angle such that the two sensors have equal output. Add a fairly
long time constant. (day-night
cycle is 1/4 degree per minute)
This web site is a fairly poor design, but the graphics should help explain
the concept.
https://www.pc-control.co.uk/howto_tracksun.htm

-Denny










On Sun, Sep 2, 2018 at 12:50 PM David C Brown <dcb.home@gmail.com> wrote:

> I am attempting to design a solar panel positioning system for use on a
> small canal boat.   This will obviously use an alt-az positioner and the
> azimuth is straight forward but the altitude is somewhat more difficult.
>
> The obvious solution of mounting the panel in bearings at its centre of
> gravity and driving the axle would have the panel too far above deck when
> stowed at zero altitude.
>
> So I cam up with the solution shown in the attached drawing.   The panel =
is
> hinged at its lower edge and a motor behind the panel drives an arm which
> bears against the back of the panel.
>
> My problem now is I can't for the life of me calculate the torque needed
> from the motor.  Could some kind soul point me in the right direction
> please
> ?
> [image: Capture.JPG]
> __________________________________________
> David C Brown
> 43 Bings Road
> Whaley Bridge
> High Peak                           Phone: 01663 733236
> Derbyshire                eMail: dcb.home@gmail.com
> SK23 7ND          web: www.bings-knowle.co.uk/dcb
> <http://www.jb.man.ac.uk/~dcb>
>
>
>
> *Sent from my etch-a-sketch*
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.