Well you have convinced me that a lead screw is a better arrangement. The problem with a close loop design is keeping the sensors clear of obstruction, especially the azimuth ones which would be very low on the deck and easily obscured by ropes, buckets etc. Whilst canal boats are mobile they move very slowly and are subject to minimal pitch and roll. Yaw would be taken care by an electronic compass. __________________________________________ 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 *Sent from my etch-a-sketch* On Sun, 2 Sep 2018 at 21:24, Denny Esterline wrote: > Approaching this with a full analytic solution is probably pointless. Eve= n > 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 lo= ad > would be a significant portion > of the power from the panel. Running the same motor through a leadscrew o= r > 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 stati= on > 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 expla= in > the concept. > https://www.pc-control.co.uk/howto_tracksun.htm > > -Denny > > > > > > > > > > > On Sun, Sep 2, 2018 at 12:50 PM David C Brown 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 th= e > > 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 wh= en > > stowed at zero altitude. > > > > So I cam up with the solution shown in the attached drawing. The pane= l > is > > hinged at its lower edge and a motor behind the panel drives an arm whi= ch > > bears against the back of the panel. > > > > My problem now is I can't for the life of me calculate the torque neede= d > > 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 > > > > > > > > > > *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 > > > -- > 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 .