PLC Virgin- Selection and Project Help

Hello everyone!

I am a senior engineering student who is about to begin the final stages of his senior design project before graduation. Anyways, my project involves the selection and implementation of a microcontroller and I have no idea what I am doing. Here are the facts I believe to relevant:

I have programming experience in C and MatLab.

I have to program two rotary motors to track the sun as it moves throughout the sky, both daily and yearly. There are set equations based upon the time of day/year and latitude. I need to program these equations for utilization by the motors via a microcontroller. This means that the motor will be moving incredibly slowly. A matter of 180 degrees in about 12 hours (depending on latitude).

Here is the motor we plan on using:

PDE7 Solar Tracking Worm Gear Slew Drive

http://rtrengineering.en.alibaba.co...sion_Solar_Tracking_Worm_Gear_Slew_Drive.html

I will need a way to input the time, date, and latitude(can be by laptop).

Let me know if there is any other information I might be able to give. I am looking for a relatively easy-to-implement controller, as I have never done anything like this before.

Thanks.

We'd need to know what kind of motor and what kind of feedback it has to make a recommendation and the Alibaba page isn't clear on that. Once you know what kind of drive you need and what kind of feedback back you will have, then we can tell you the cheapest way to do what you want.

Oddly, they seem to offer AC and DC motors but not stepper motors, which I would think would be nice and cheap for this; just do one step every X amount of time.

As far as controller recommendation, if you don't have a requirement to use a PLC (and don't need a crazy drive for the motor), use a Raspberry Pi. A PLC is going to cost more. If you really feel like blowing money, B&R has their compact X20 PLCs and may give you a price break for being a student, or better yet, donate the equipment to your school.

Kunim said:

Hello everyone!

I am a senior engineering student who is about to begin the final stages of his senior design project before graduation. Anyways, my project involves the selection and implementation of a microcontroller and I have no idea what I am doing. Here are the facts I believe to relevant:

I have programming experience in C and MatLab.

I have to program two rotary motors to track the sun as it moves throughout the sky, both daily and yearly. There are set equations based upon the time of day/year and latitude. I need to program these equations for utilization by the motors via a microcontroller. This means that the motor will be moving incredibly slowly. A matter of 180 degrees in about 12 hours (depending on latitude).

Here is the motor we plan on using:

PDE7 Solar Tracking Worm Gear Slew Drive

http://rtrengineering.en.alibaba.co...sion_Solar_Tracking_Worm_Gear_Slew_Drive.html

I will need a way to input the time, date, and latitude(can be by laptop).

Let me know if there is any other information I might be able to give. I am looking for a relatively easy-to-implement controller, as I have never done anything like this before.

Thanks.

Click to expand...

PLC's range from small devices with only a few output signals to expensive devices that control whole factories. What you need is probably a "micro" PLC. This is the market segment with the most choices. More options is good, but it also can make the decision very hard if you don't know where to start.

If you are looking at a PLC for this task, I would suggest you find one that supports the languague called SCL or Structured Text. Of the major PLC languagues, it is the most similar to the traditional PC programming that you are familiar with. Most PLC programming is done in a graphical way, something along the lines of labview or lego mindstorms. Honestly, the normal programming for PLC's (Ladder Logic) is pretty easy to get a hold of, but sometimes can be limited. It was essentially created to allow electricians to easily understand,

You will also need a PLC that supports math with floating point numbers, if you want to do solar tracking. Not all of the small/cheap ones do so be sure to double-check this.

Out of mish mash of brands, there are a few that stand out as big players. Rockwell/Allen Bradley is the biggest PLC vendor in the US, and if you go this route you will probably be most likely to find assistance. Siemens is the biggest PLC vendor globally (and the one I'm most familiar with), so they can be a good option as well. Automation Direct specializes in these smaller micro PLC's, and they are pretty popular on this forum. I've heard that Beckhoff allows C programming directly, so that might be something to look at, if that is your familiarity.

The link below shows an implantation for the sun position algorithm on a Siemens S7-1200, in SCL.

http://www.bytex.it/Article/eng/Com...ple-code-with-Siemens-S7-1200-Tia-Portal.html

I know Siemens used to have sample projects for the 1200 that actually had a full solar tracker demo, which included HW recommendations, wiring diagrams, and everything. They might still be floating around the net somewhere, but I could only find references, not the whole project.

CapinWinky said:

Oddly, they seem to offer AC and DC motors but not stepper motors, which I would think would be nice and cheap for this; just do one step every X amount of time.

Click to expand...

From what I've seen with solar applications, they need low speed and high torque to move a huge panel throughout the day. This makes a simple, cheap motor with a big gear box a great solution. When you move that slowly, accuracy becomes much less of a concern. Interestingly, the sun moves at completely different speeds throughout the day. Trackers need to move much faster (though still pretty slow) around noon than they do in the evening.

CapinWinky said:

As far as controller recommendation, if you don't have a requirement to use a PLC (and don't need a crazy drive for the motor), use a Raspberry Pi. A PLC is going to cost more. If you really feel like blowing money, B&R has their compact X20 PLCs and may give you a price break for being a student, or better yet, donate the equipment to your school.

Click to expand...

He makes a great point here. There are advantages to a PLC, but for a school project, something like a raspberry pi or an arduino would be cheaper and possibly simpler. If you do want a PLC, definitely mention your student status to the vendors. A lot of them would love the chance to get their hardware into a university.

Look at Texas Instruments development kits. I recall their 'C32 DSP, which has been around for 20 yrs. Also the MSP430 microcontroller that has some analog I/O. You can find a book on the web for developing projects with it. Besides development boards (one on a USB stick), it comes in a DIP package for easy proto-typing. If it will be all digital, there are PLD's or even FPGA's. PIC chips have long had a following, and are the basis of the "Basic Stamp" (many books) and the Lego robot kits, but I think the newer Raspberry Pi displaced them. You can find fairly cheap used development kits on ebay, some unopened from companies who bought to try and never got around to it. Your PC could run a user's supervisory program for HMI. Your app is so slow that you could run the real-time app on the PC, but using the micro's would be more instructive and sounds like what the teacher expects. While Raspberry would work, they are considered "hobbyist", so the TI products might give a more professional image.

Hey, everyone.

I have an update. Our motor has changed, but I have the spec sheet here for the new motor. Our budget has shrunk and simplicity is the name of the game now! So, the easiest method of programming this motor would be ideal!

Thank you very much!

Rated Voltage: 24V
Motor Rated Speed: 1900rpm (obviously mine will not be moving this quick)
Ratio: 236
Rated Current: <1.8A
IP:55

Kunim said:

Hey, everyone.

I have an update. Our motor has changed, but I have the spec sheet here for the new motor. Our budget has shrunk and simplicity is the name of the game now! So, the easiest method of programming this motor would be ideal!

Thank you very much!

Rated Voltage: 24V
Motor Rated Speed: 1900rpm (obviously mine will not be moving this quick)
Ratio: 236
Rated Current: <1.8A
IP:55

Click to expand...

You're missing some key info here: what are your requirements?

Are you required to use a PLC, or can it be any kind of controller? An arduino might fit better with your C experience than a PLC. A PLC, however, is designed to control its IO, so it might make interfacing to the real world HW easier.

Do you need to use the solar tracking algorithms, or can you use something simple like a sun sensor?

http://www.instructables.com/id/Arduino-Solar-Tracker/

Is this closed loop or open loop control? Are you getting feedback from the motors? Are you simply powering them for a brief period and then turning them off, hoping they moved the correct amount? In my experience, having high quality feedback is the most critical factor in accurate control.

How accurate does the solar tracker need to be? Some kinds of panels require 5% accuracy, some require .05%.

One other thing to note: if you have any linear actuators involved, instead of all rotary motors, be prepared to do some trig to model your system. Moving an actuator one inch corresponds to a different number of degrees, depending how far it is extended/where the tracker is pointing.

I am not required to use a PLC. I do have to use the solar tracking algorithm, however.

This solar tracker simply needs to work one day. Which means, open loop should be fine, however they would need to be powered for a significant amount of time, in addition to locating the sun in the sky from some set "zero" position and positioning accordingly. Incredible accuracy is not required. No larger than 5% inaccuracy should suffice. There are no linear actuators, only rotary slew motors(rotating thread aligned with "geared" bearing generates perpendicular axis rotation).

Kunim said:

I am not required to use a PLC. I do have to use the solar tracking algorithm, however.

This solar tracker simply needs to work one day. Which means, open loop should be fine, however they would need to be powered for a significant amount of time, in addition to locating the sun in the sky from some set "zero" position and positioning accordingly. Incredible accuracy is not required. No larger than 5% inaccuracy should suffice. There are no linear actuators, only rotary slew motors(rotating thread aligned with "geared" bearing generates perpendicular axis rotation).

Click to expand...

Ok, if you are OK with open loop control, you could probably use any of the control options people have mentioned above.

If you get a small PLC (like an S7-1200) that has relay outputs, you could probably control power your motors directly from that. Solid state outputs are typically rated for only .5A at 24V, but relays are typically rated for at least 5A. Most small PLCs either have free or relatively cheap programming software (likely only a couple hundred dollars), but you would need to make sure you select a PLC that supports the advanced floating point math you would need for the solar calculations.

You could also use something like the arduino, but that would probably need external relays to power the device. THis is probably closer to what you are used to programming, and will probably be cheaper as well.

Thank you so much guys for your responses.

I think I am going to go with an Arduino. However, while browsing the Arduino website, I have found there to be a vast number of options. How can I decide which would be the best for my application?

EDIT: Or would the Raspberry Pi work better?

I think either would work, so look at ease of programming and I/O wiring. I think both are sold at hobby shops (even Radio Shack), though buying used on ebay should be much cheaper. I am sure grandparents give them to stimulate little Johnny, but he prefers playing to developing, so an unopened box to off-load.

Re drive, a simple mechanical automotive relay (30 A) would work. If pressed for funds, borrow a non-essential one from your car (ex. sun-roof this winter). You can wire w/ individual "56 terminal" spade connectors (common in home appliances) or buy a wired base on ebay. Actuate by >8 V on the coil (85 to 86, or vice-versa look for a diode symbol), which connects source (30) to output (87).