Discussion in "Project Help" started by    rebelharsha    Mar 5, 2009.
Thu Mar 05 2009, 05:23 PM
#1
Its a final year B.E project.. We are using two LDR s in potential divider circuit to track the sun direction... A small triangular mounting placed above the panel is used wit one ldr on each side of mounting facing east n west respectively for the above purpose.... we are finished wit the sensor circuit part...... We are yet to decide the type of microcontroller and stepper motor... AT89c51 and AT89c2051 are the two mics we have short listed for this job... But the problem is there are no burners available in our city... N also the stepper motor should be able to rotate a panel or equivalent panel model of around 1 to 2 kg weight... I need the microcontroller along with its burner details and Cost n also the stepper motor specifications for our project... Can u please help...? Dead line for our project is by this month end....... Also is it okie to use a bredboard to make the connections for the microcontroller wit external oscillator n other connections OR we should go for a development kit for microcontroller?
Thu Mar 05 2009, 07:45 PM
#2
You can make use of P89V51RD2, its available easily in market and it doesnt need a programmer. A simple serial port is needed to program it. and you can download flashmagic software to program it.

regarding your panel model.. why you've made it so heavy??? 1Kg? huh! thats too heavy. i think you people should work on the panel again. motors.. look for anything you can find in market. its better if you guys can use a DC motors, coz they are cheaper. just try if you can find steppers at reasonable price.
Thu Mar 05 2009, 09:10 PM
#3
Sounds like an interesting project.
You will need to use gearing anyway, so you will not need a big motor.

If the unit is well balanced, weight will not be a problem, but the wind could be.

Did you consider using the Micro to 'know' where the sun is by keeping track of the time ?
Thu Mar 05 2009, 10:51 PM
#4
Fortunately, even if the weight is large, like Philip said, the smaller motor will work fine. Just remember these simple rules about motion control:

Torque is multiplicative with gearing, so tiny motors can do big jobs, but at a slower pace.

Inertia is reduced by the square of the gearing, so even large loads, as long as they don't need rapid acceleration, can be moved by small motors.

One more thing: encoder feedback for positional information should be less than 1/2 the resolution of the motor, so single motor pulses can resolve positions to align with fractional encoder ticks.

This projects sounds interesting and challenging! Hope I can help along the way...

-Dave
 rebelharsha like this.
Fri Mar 06 2009, 06:32 PM
#5
Hello Dave... Actually we hav been asked by our project guide to finish a prototype of our project before working on with real solar panel by this month end... So we may use 20 by 10 rectangular thermocol model instead of panel.. I guess now panel weightage problem is not much of concern... But i would love to learn more about gearing and torque of stepper motors..
I dint understand your last sentence about encoder feedback.. So can u please elaborate more on stepper motor part and its driver circuit...
Fri Mar 06 2009, 06:46 PM
#6
Hello Ajay... Can u please tel me more on tat P89V51RD2 chip.. I dint get much info on that. Is tat comes wit a kit like structure or something? I mean wit required I/O ports and serial ports for programming.. Also i even asked about whether is it feasible to rig up microcontroller circuit on a bredboard providing external oscillator circuit and other required connections?
Sat Mar 07 2009, 03:50 AM
#7
You can learn more about gearing and torque/reflected inertia from just about every motor manufacturer. Usually, they have an engineering application handbook you can read. A quick Google search for "gearbox inertial load" landed this interesting article:
http://www.imshome.com/Product%20Manual%20PDF/gearbox_inertia.pdf

Regarding encoder feedback: If your encoder is attached to the thing you are moving, and you use the reading from it to decide how to move, then your method of moving should be more precise than the resolution of the object being moved, eg: the encoder.

Consider a 6.366" diameter table, that has an encoder attached to the table with a resolution of 2000 ticks per revolution. This would mean the perimeter of the table would be 20", and the resolution of the encoder (at the edge of the table) would be 1 tick every 0.010 inches. Well, if you were trying to resolve the position of the edge of this table to 0.010 inches, you would want a motor capable of making steps smaller than 1/2 of this distance, or less than 0.005 inches. This means your motor plus gearing should be more than 40k pulses per rev.

Why? Because the level of uncertainty for each step would be within 1 encoder tick position. The smaller you make the motor steps, the more you can reduce the positional uncertainty (approaching the accuracy of the encoder itself) by increasing the resolving accuracy.

I hope this makes sense.

-Dave


[ Edited Sat Mar 07 2009, 03:51 AM ]
Sat Mar 07 2009, 01:17 PM
#8
Hello Philip...... As u suggested we are also using a timer to keep track of sun along with the sensor circuit as a back up option... I guess the assembler code wil be ready by this weekend.. Only problem is rotating the panel model using motor and gearing stuffs..
The structure tat holds panel n motor!!! we don know much about these stuffs.. So lot of suggestions are warmly accepted... Please help...
Sat Mar 07 2009, 01:21 PM
#9
Thanks dave... i understood most of ur explaination... i wil look into that site n try learn more on those stuffs... please keep in touch....
Sun Mar 08 2009, 09:48 AM
#10

Hello rebelharsha,

you can also check out our friend Binu.J's "Solar Tracker" project here:

http://www.8051projects.info/proj.asp?ID=33

its a nicely done project and the code is well written (in ASM).



Arun

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