Greenhouse rollup motor control

Projects General Guidance
1

Hi,

I am a complete newby to Arduino, though I have an Uno and done a bunch of the little projects with LEDs etc. I am a farmer and would like to figure out how to control the motors that roll the sides of my greenhouses up and down. This is not a backyard greenhouse like in many of the Garduino type projects out there - its a serious 3000 square footer with 100 foot sides. We have 4 of them. The motors that roll up the sides are quite expensive ($300 each), and I currently just have a hand rolling setup.

The reason to do this is mainly practical. A controller and driver from a greenhouse supply company is over $1500, and it seems like an arduino and some off the shelf controllers should work. However, I don't know how to ensure that I get the proper driver for the motors I need, so that it won't just burn them out and waste a bunch of money.

The motors can be seen here: http://advancingalternatives.com/index.php?main_page=index&cPath=1455_1463_1465_1468

I am thinking of using a motor driver like this: http://www.robot-r-us.com/motor-driver/md22-24v-5a-dual-h-bridge-motor-driver.html?redirected=1

There are so many different options for motor drivers, I have no idea how to identify the absolute cheapest option. The arduino would simply have to check the temperature every minute, and tell the motor to either rollup one turn, roll down one turn, or do nothing. It seems this is very simple compared to what these drivers are designed for, which is usually some kind of robotics application.

Any ideas or suggestions would be greatly appreciated. Also, any ideas about housings that would be relatively weatherproof, relays, and all the in between parts like fuses and such that would protect everything. Sorry I'm so dumb, but I am a farmer, eh!

thanks,

Robin the farmer

2

couple of thoughts.

First, the absolute cheapest. that is really not a good way to design.

the 24V motor looks like a great device and at $300, it is clearly not low cost.

the arduino would be a great place to start.
get an arduion, a data loogging shield and a couple relays. a twin relay or a quad would be fine.

log the temperatures so that you get a feel for the project.
if you have any regular 1/4 hp motors, 120 volts, you should be able to add a couple jack-shafts and pulleys to get it geared down a little bit. connect that to your hand crank. let it raise the side for you.
if you like dumpster diving, get a garage door motor assembly, they are usually geared down pretty well.

you will need upper and lower limit switches. when you install them, have the curtain slide past to activate. do not dead end into them.

if you can get the curtain to raise by turning the motor on every couple minutes, it will not overheat.

3

first choose what motor you wish to interface.
for example 24vdc motor
than choose what switches you plan to use for stops.
now in the sketch state the names for these these things
exp. int 24 vdc motor
int lower switch
int top switch
you have now defined the names for the devices you wish to use.
After that comes the operation.
I hope this helps at least with the thought process

4

That motor/driver combinations seems like a reasonable fit, and it's convenient that the driver provides several modes for speed control. These things will be more reliable if you keep them well below their nominal rated power levels, and you can do that easily just by reducing the motor speed/duty cycle. Trial and error will soon tell you how much power you need to get the operating speed you need.

It would be possible to get the motor/gearbox/driver components quite a lot cheaper if you were willing to spend more time fiddling about on that side of things - there are plenty of automotive motor/gearbox assemblies that will generate the sort of torque you'd expect from a hand crank, and can be powered easily via some cheap 12V relays which can be driven by any cheap driver shield/board.

I assume you'd plan to have some sort of temperature feedback algorithm, and that's where you really will need trial and error to see what works. There's a PID library for the Arduino, but that might be overkill for this application and perhaps you just need a proportional control algorithm.

If you want to add scheduled operation, or remote control, or data logging, this all adds to the software complexity but it's all doable and just needs time and effort to develop. I suggest you keep it simple to start with, though.

5

The motors can be seen here: http://advancingalternatives.com/index.php?main_page=index&cPath=1455_1463_1465_1468

Given your statement that you currently have "hand operated rollers" have you actually verified that this motor is suitable for operating the window covers? If so what were your considerations (torque, etc.)?

One concern is that the specification for the above motor is incomplete, as the listed current of 3 amps is almost certainly the running current under some typical (unspecified) load, and the stall current will be quite a bit higher. Typically the stall current is 5-10 X the running current or 15-30 amps. If so, the motor driver you have chosen will not be adequate, as DC motors briefly draw the stall current when starting up. I suggest to write to the manufacturer and request the stall current specs, as well as the test conditions for the claimed 3 amp running current.

If those motors turn out to be suitable, Pololu offers motor drivers that can handle them. It would be straightforward to do what you want. Pololu High-Power Motor Drivers

6

Thanks for all the responses, definitely encouraging. As for the motor itself, it is specifically designed for rolling up the sides of greenhouses. This one is designed for sides up to 250 feet long and six feet high, so I would assume its strong enough for my 100 foot greenhouse.

As for the peak amperage, I would be surprised if it is 10x the operating amperage as it works at only 2.7 rpm. I'm not sure if that's what the actual motor runs at or if the blue thing is just a gearbox that outputs that. . . 30 amps does seem like a lot though. In any case the motor shield I found and link to below supplies 30 amps peak.

What I need to replace with the arduino is this thing here: http://advancingalternatives.com/index.php?main_page=product_info&cPath=1441_1450_1452_1454&products_id=4099

Which as you can see is $1000 for two motors. We need four of them to do four greenhouses, so the potential savings are pretty high. I would be totally into using a different type of motor, though for three hundred bucks with all the attachments, etc to fit on my greenhouse, it's not that bad. Again, I just don't want to fry it, and I'd need all the right relays, diode, fuses, etc in a nice neat box.

I'm wondering if this would work for a power supply: 24V, 10.0 Amp Single Output Switching Power Supply | Circuit Specialists
Then this motor shield has the specs I'm looking for here: http://www.robotshop.com/ca/en/pololu-dual-motor-driver-shield-arduino.html

With an arduino shield it seems like you wouldn't need relays? Is that correct? So I'm imagining the AC power running to the power supply, which puts out 24v to the shield, which then runs the motors. Do I need any other doodads in between like fuses, etc?

I'm also imagining that with the shield on the arduino it's still possible to hook up a temperature sensor to control the motors. True?

Just to keep it in perspective, the parts I've listed so far are $55 for the shield, $30 for the arduino, and $40 for the power supply. Throw in a case and wires and all that and it would be easy $200 per greenhouse. Still a big savings over $1000 bucks, and also able to be expanded via the arduino's ports in the future to all sorts of exciting stuff.

Thanks for all your advice so far!!

7

If the choice of actuators is still open then given the prices of the components you're proposing I'd want to get a better understanding of your real requirements and not just choose parts that are advertised as suitable for greenhouses.

Are you intending to replace each hand crank with a motor/gearbox? That seems like the most sensible approach i.e. replace the manual drive rod with one that is connected to a motor / gearbox. How much torque does it need to apply to the drive rod (i.e. in foot-pounds or newton-meters)? Presumably you're happy for this to be as slow as necessary which means you can get away with relatively small motors as long as you can gear them down far enough. The smaller the motor the easier and cheaper everything else will be.

8

the motor is slow speed, high gear reduction.
you may be able to power it with 24VDC directly and not require a motor speed controller.

I am not sure of the motor characteristics, but it is not too hard to make a current limiting circuit so that the motor can stall and not overheat. check the power supply you plan to use. it may have over current protection so you may not need to do anything.

turn the hand crank so that that the driven shaft rotates 1 revolution. how high did the side wall lift ?
you should be able to just use relays and power the motor for short periods. the motor says 2.7 RPM at full speed. if you power for 15 to 30 seconds, it would roll up some distance.

if you set up a data logger and test. have the program beep a beeper when it wants to move, you move 1 revolution and press a button. the data logger will note the change and later, you can watch the result. if 1 revolution is good enough, then you do not need a speed controller.

the nice thing about using the Arduino is that you could also water and turn on fans.