My problem is the voltage ratings of these motors.
I know that the torque developed by the motor is proportional to the current through it but I am not sure how the voltage applied affects it.
The question is, can I use a simple L298 based motor driver to control these motors. L298 IC can handle a max of 4A at a time, which is more than enough for these motors. What about the voltage. How can I provide exact voltage (3.3 V or 3.2 V) to the motor. Will a simple potential divider work? What if I don't give the exact voltage and instead give a 5 V or 12 V supply to the motor?
The motor driver board that I am planning to use has only one supply. It then uses a 7805 voltage regulator to supply the L298 IC.
If I jack it up to a RPS at 3.3 V & 2 A, will it work ??
As thousands of posts in these and other forums attest, the L298 motor driver is vastly overrated and cannot be used for motors that draw over about 1 ampere per winding. It will simply overheat and shut down. The chip is also quite inefficient and "wastes" 2-4 volts of the power supply voltage.
In fact, there are very few motor drivers on the hobby market that can handle even 2 amps/winding, but the modern current limiting chopper drivers allow you to set the motor current to a tolerable value. Furthermore you can get much higher resolution with microstepping. Take a look at Pololu's offerings, e.g. the DRV8825 Pololu - Stepper Motor Drivers
Edit: the voltage rating is just the maximum steady state DC voltage that may be applied to a winding, which leads to the maximum allowable steady state winding current.
The voltage ratings on stepper motors are very misleading. Taking account of the resistance of the coils those are the voltages that will drive the maximum current through a stationary motor. However most people want stepper motors to move. And then the back-emf of the coils significantly reduces the current unless the voltage is increased. The "proper" stepper motor drivers like the Pololu A4988 are designed to limit the current to the allowed maximum even with voltages up to 30v.
The A4988 can't supply the full current for your motors. The current available from the A4988 (2A absolute max if there is sufficient cooling) may be enough for your application. If not there are plenty of high current stepper drivers for sale - search EBay - though they will be more expensive.
If not, I will have to think of some alternatives for the steppers. Maybe low RPM DC geared motors.
Actually I am trying to make a dual axis solar tracker. Steppers have very precise position control, that's why I wanted to use stepper. Precise position control of DC motors is difficult.
The panel I am trying to move is 1.2kgs & its dimensions are 345x350x11 mm.
The industrial grade microstepping driver in your link 1. looks quite nice and will certainly be adequate. However, I don't think there is a compelling reason to use stepping motors. They are accurate only if they don't slip or skip steps, and it would require quite a bit of design and experimentation to make sure that this cannot happen when the device is actually functional.
The alternative is to have some sort of positional feedback, which will work for either steppers or DC motors. Finally, you will have to have some sort of gearing arrangement to couple any motor to the panel support, so in the end both solutions seem equally feasible.
A major problem with stepper motors in the sort of application you mention is that they consume a lot of power all the time to enable them to hold position - probably more than the solar panel produces. And a solar panel does not need to move often.
A better alternative (and probably much cheaper) would be a DC motor with a worm drive. Second hand car windscreen wiper motors may be very suitable. The advantage of the worm drive is that it holds position without any electric power.
If you are using optical sensors to orient the east-west alignment there should be no difficulty coding a suitable feedback system. And you could use a potentiometer to give position information for the azimuth (hope that's the right word) drive. You could probably use a potentiometer for the east-west position also.
Stepper doesn't seem to be the best choice here. Its expensive compared to geared DC motors and if the load happens to be too much for the stepper to handle it will start wobbling. I checked out some videos, its bad.
It will be best I find DC motors for the purpose.
Ya, there will be some kind of gear arrangement, I haven't designed it yet.
Ya, now I am seriously reconsidering steppers. Doesn't seem to fit the purpose.
I will surely try to check out the car windscreen wiper motors. Seems very reasonable.
I am tracking sun by following the power obtained from the solar panel ( 10Wp). No optical sensors. Just current and voltage sensors. Then simple hill climbing algorithm. The motors will have to go bit back and forth to find the exact point of max power.
I don't know what part of the world you are in, but in the UK the output from solar panels varies widely over the space of a few seconds as clouds obscure the sun. I can't see how a "hill climbing" system could cope with that.
Also, the position of the sun is very predictable ...
Ya there is rapid change in output, but I think you can stabilize that by taking average of some values and then using it for the algorithm.
The position is predictable, you are right, but I am trying to make this work by just using current and voltage sensors. Which is inherently present in most off-grid or grid-tie systems. Thereby avoiding use of photo-based sensors or astronomical methods.
The device below (an automotive window regulator) may be a good solution. Inexpensive, readily available, powerful, and holds position with no power applied. I incorporated it in a solar panel tracker I was working on. I don't plan to try to track the sun's zenith since it wouldn't need constant adjustment and could be done, in my case, manually. The motor draws about 9 amps at locked rotor. I used a relay driver board to apply power. - Scotty
AbhishekAnand:
I am in India. Manipal to be precise.
Ya there is rapid change in output, but I think you can stabilize that by taking average of some values and then using it for the algorithm.
The position is predictable, you are right, but I am trying to make this work by just using current and voltage sensors. Which is inherently present in most off-grid or grid-tie systems. Thereby avoiding use of photo-based sensors or astronomical methods.
Astronomical methods have been working well for 5000 years or so.
The concern I would have with orientation based on the power output is that it's most important to have the solar panel pointed in the right direction when the solar energy is momentarily obscured so there is no hunting around (and uncaptured energy) when the clouds clear. In other words, loss of power should not be a signal to go searching for the sun in a different part of the sky.
If you don't want to use time and calendar based orientation I suggest you have 4 cheap Light Dependent Resistors (LDR) one on each edge of the panel. With a suitable shield so the sunlight only falls fully on both LDRs on opposite sides when the panel faces the sun you can use the difference to adjust the orientation. Because there is a pair of sensors they will be indifferent to the actual strength of the sunlight. It would probably also be worthwhile having a long wait (minutes?) between adjustments.
Won't different manufacturers have diff configurations, pinouts and torque ratings.
Yes. Go browsing on ebay. You can get an idea of what would suit your project just by looking at the images shown in the posts of the items. Most likely the pinouts will be as simple as you can get, negative and positive. Torque shouldn't be much of a problem if the vertical load is supported by a bearing. - Scotty
