Guys I'll start with explaining my dilemma and then hopefully someone will be able to advise or point me in the right direction.
Scenario: I'm designing/building a 2.5m parabolic dish solar concentrator. The frame will hopefully be made of Alu to keep the weight down and the mount, made from steel, will similar to a standard satellite dish mount which I originally planned to use two actuators and an Arduino Duo to track the sun. The arduino would also be used to park the dish in a safe position if the wind gets too high or the temperature of heat transfer fluid becomes to hot but my issue is the tracking.
Dilemma: To get maximum use from the sun the dish needs to track in the region of 155 degrees in the horizontal from east to west. I have been drafting and scratching my head over the mechanics of it all and whilst I think I can get a 36 inch actuator to work it would be a really close call and I'd hate to spend the money on something that might not work. My only alternative, I believe, is to use a stepper motor but to to turn a dish of that size/weight I think I'd need something pretty beefy, somewhere in the region of a Nema34 perhaps. If I go this route then I have a power problem as a motor that size will draw somewhere in the region of 6A per winding which an Arduino even with an Arduino motor shield could not cope with. So I came across a Powerlolu which will go as high as 10A but I don't know if the Powerlolu will plug into/work with an Arduino Duo. Could I use Arduino to power replays? would that be a viable alternative?
Any advise, guidance or alternative approaches would be warmly received and appreciated
Alternative might be to use a smaller motor to turn a threaded actuator (clearly speed isn't an issue), which means much less
torque is needed. I think automatic garage doors use something like this, perhaps worth checking out.
Are you tracking in 2 axes (pan/tilt), or just around a single pivot?
MarkT:
Alternative might be to use a smaller motor to turn a threaded actuator (clearly speed isn't an issue), which means much less
torque is needed. I think automatic garage doors use something like this, perhaps worth checking out.
Are you tracking in 2 axes (pan/tilt), or just around a single pivot?
Guys, thanks for your replies.
Chagrin - I'll look at the EasyDriver thanks
MarkT - a smaller motor might be an option but my concern is that it won't be strong enough to turn the dish or might not cope holding it under a strong breeze and then I'll have wasted money. I have looked into the Nema23 size but I will check out your suggestion re garage door so thanks for that. To answer your question - I am tracking on two axis as tracking on one won't really give me the efficiencies I'm looking for. Tracking vertical should not be a problem but, as stated, it's the horizontal that is the challenge. Even with a 36" actuator its a very close call where, because of the broad angle required, piston and dish's main post do come very close. If I opt for the stepper then I have the additional design considerations of main shaft bearings etc... Hopefully you'll appreciate my dilemma via the attched...
Very interesting project. Similar to one I have on the back-burner until U get the motor selection & actuation straightened out. Having fun putting together a 2 wheeled robot (inverted pendulum) in the mean time.
I know this is a relatively older post, but I was wondering if you moved any further with this and what roads it may have led you down.
The Powerlolu with its 10A capability should allow you to use a relatively large stepper which should provide you with enough torque. I've been working with the L6470 Autodriver, but it only goes up to 3A.
As MarkT mentioned. His comment about the fact that the movement does not have to be fast and (and infrequent) also suggests maybe some sort of gearing (down) that will increase torque on any motor.
if you, or anyone still interested in this link, are still around, give a shout out - I'd like to breathe some life into this subject again.
There was another long Thread about a similar project recently - Google should find it for you.
I am not convinced that stepper motors are appropriate - they are very inefficient and may consume more energy than you can capture. They need to draw their full current even when stationary if they are to hold position.
Regular DC motors with a worm drive provide lots of torque and can be switched off without losing position. Used car windscreen wiper motors might be useful.
