E-Chicken Tractor

[mechanix]

Hi all,

I'm in senior design for Mechanical Engineering at Oregon State University, and my group is designing a fully-automated chicken tractor. Basically it's solar-powered, fully automated (moves a certain distance in a given direction per day, think "roomba robot"). The main microcontroller for this tractor is an arduino mega2560. I attached a pdf of our preliminary Proposal, which gives some of the details of the design for the people that care.

Here are some pics of the basic frame to get an idea what it will look like:

angled view:


side view:


My first question is for the motor/controller gurus out there-- How to control this motor? We chose to use a starter from a John Deere tractor to power this unit and our budget is limited to under $150 to control this motor. The specs are as follows:



The tractor will weight close to 400lbs when finished, with the gear reduction (two-stage #35 chain) it should move at 2-3 mph.

We were thinking of two ideas:
1. Use a very beefy relay and have the arduino interface with the circuitry for the relay. The on/off nature of this design should be ok, as we have torque limiters to help with the shock to the drivetrain.
2. Find a cheap brushed controller that is 12v and can handle the insane amount of amps this motor will draw and use the arudino to modulate the throttle.

Any ideas how to control this beast?

Cheers,

Joel

[will_newton]

i tell you one thing. the chickens won't give a shit.

[neptronix]

Man. That is a lot of money and effort VS lettin' em free range.

Personal politics inside, interesting idea. This motor doesn't have to operate for too long.. so you can run it far over spec - nice.

[mechanix]

yeah, I agree, it's a very unsustainable idea. Most people will see it with the solar panels on top and think "Green!". In reality, the resources that go into making the aluminum for the frame, all of the electronics and the solar cells themselves is immense. It is what it is, so I'm just trying to design it as bombproof and simple as possible so it will actually last and not be a bigger waste by breaking down after a couple months of operation. One of the reasons for making it is to appeal to the public during an Earth Day get together here in Corvallis. Either way, it's going to be really fun to build, and it's kind of nice not to be spending my own money on a project for once!

So... any ideas how to control this motor?

Joel

[mechanix]

Will, the chickens actually will give a shit, it's one of the many benefits they provide to the soil!

[nieles]

there are some cheap RC brushed controller on ebay:

http://www.ebay.com/itm/Lastest-320A-Hi ... 3a6e27c5f5

or you could mod one of these:
(you will need better fets, probably more caps)
http://www.ebay.com/itm/24-VOLT-250W-Br ... 2a1740e227

[Hillhater]

I see dead chooks in your future !
dispite the low speed, those birds are so incredibly dumb, you just know some of them will be run down by this unit on the first day !

[mechanix]

Hillhater-- It only moves at night when the chickens are roosted. (if everything goes as planned, that is)

Nieles-- I think I'm going to need a controller with about 10-20x the power handling capabilities of those controllers, although that ebike controller is super cheap!

Does anyone know of any cheap, extremely high amp relays or contactors? I think I might have to make my own "controller" (basically an on-off switch)

Cheers,

Joel

[nieles]

how much power do you really need?

with the controller you can ramp the acceleration, so the power consumption would not be very high right?

if you use a contactor, the motor will try to ramp up to max speed instantly, and the ampdraw will skyrocket

i dont think you will find a cheap controller rated for 500-700A

the best option would be the bike controller modded with some low rdson fets IMO

[Drunkskunk]

you shouldn't need those amps to move a 400lbs box at slow speed on reasonably flat ground. all you need is a good amount of torque, which can be had by gear reduction.

Those mobility scooters that move 400lbs women up wheel chair ramps into the Local McDonalds or Walmart are running on FAR less power, and greater speeds than you'll need.

I bet if you increase the voltage, and increase the gear reduction on that motor, you can get by with a 20 to 30amp brushed DC scooter or wheelchair controller.


That tractor motor may work at 24 to 36 volts if you keep the amps limited to 30 with the controller. but it may not be the best motor for the job. Starter motors have a short duty cycle and are inefficent by nature, designed to make huge torque for a few seconds but not run very long.

[REdiculous]

I'd make it slower and run it on the solar directly. A sensor on the inside could be used to temporarily stop the coop, like the way it works at checkout at the grocery store, so it can't run over the occupants.

It would need to be a little slower since it'd be on and moving most of the day, but then you're not storing power and having to control when and for how long the thing runs.

[mechanix]

@Drunkskunk: lol about the mobility scooters... we're set on 12V due to the solar panels, charging system and batteries. I think I'll just track down a 12V golf cart controller and call it a day.

@REdiculous: One of the requirements is for it to move only at night to avoid the carnage that would ensue if it moved during the day.

I'm thinking this would be a good option:

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 97.c0.m619

Cheers

[mechanix]

After looking more closely at those controllers on ebay, I found out the they are for sepex motors (four terminal). Can a sepex motor controller run a normal brushed dc motor if the terminals are put in parallel? I'm guessing not, I'll just have to keep an eye out for a cheap golf cart controller or something.

[Hillhater]

I suspect your motor is too powerful. Try sourcing a small motor bike / lawn mower starter.
Then, as with the starter motor operation on a car etc and with the low speed... just use a on /off relay.

[E-racer]

You do not need anything near the size of a golf cart controller to move a 400lb box at 2.5 mph. You also don't need 2,500 watts (btw a pair of RC car controllers can make more than 2,500 watts). You need max 600w and that's if its extremely hilly and a really bad inefficient drive line. Hell a decent pair of cordless drills would probably move a 400lb box at 2.5 mph. Please realize 2500w will move a 300lb bike and rider over 30mph. Contractors or relays will not work for tank drive applications because you cannot vary the speeds of the wheels to control the amount that the vehicle turns. Good luck with your build. As a senior in college as well I can tell you this project could be excellent! This is no high performance EV though, don't over spec your power requirements. The less power you use the more affective the solar setup.

BTW. if you don't take my advice this $119 Kelly will controller that motor to its fullest potential 12V x 200 amp = 2400 watt http://kellycontroller.com/kds24200200a12v-24v-mini-brushed-controller-p-76.html

[Hillhater]

...Contractors or relays will not work for tank drive applications because you cannot vary the speeds of the wheels to control the amount that the vehicle turns. [/url]

Who mentioned varing speeds for turns ??
And anyway tanks/ tracked vehicles do steer by exactly that method of simply stopping the drive to one side.

Does anyone know of any cheap, extremely high amp relays or contactors?

yep ! .. same place you get the starter motors from ! ... Auto starter solenoids.

[mechanix]

We went with this powerful of a motor to to simplify the design. There's already so much programming going on, we didn't want to also have to deal with a position feedback system. The solution was to get a very powerful motor and instead of feedback, it just runs for a set amount of time to determine how far the tractor moves. Also, this starter was very cheap and powerful things are fun, right?

I'm not a motor expert or an electrical engineer, but looking at the spec sheet for the motor, it looks like it might have the potential to ruin small controllers. It draws 150 amps at no load, so I think that it will need a pretty hefty controller. I believe that a very low winding resistance is the reason why this motor draws so much current.

So my question to all the motor/controller experts out there is:

what controller does this beast of a motor need, or should I just use a relay/contactor/solenoid for an on/off type design?

yep ! .. same place you get the starter motors from ! ... Auto starter solenoids.

Thanks, hillhater! It was right under my nose the whole time!

[nieles]

if the no-load amp draw is 150A @ 12v. you will be wasting 1800W of heat.
that doesnt seem right. i would go for a more efficient motor

like this one:
http://banebots.com/pc/MOTOR-BRUSH/M4-R0062-12

[mechanix]

yeah, you're right... I guess we'll have to search for a different motor. 1800w is like a space heater inside that little can. Problem solved, thanks guys!

Joel

[REdiculous]

One of the requirements is for it to move only at night to avoid the carnage that would ensue if it moved during the day.

If you have to move at night, just take one step and you're on fresh land...lol..

I'd still make it slower and run it during the day. There shouldn't be any carnage ensuing since you can use simple sensors to stop the machine when animals enter the danger zone. If it covers its length every hour, on average, (for example) it would be on fresh land a lot more often, rotating around the pasture more frequently (though still slowly!).

Just the way I see it. *shrug*

[Hillhater]

There shouldn't be any carnage ensuing since you can use simple sensors to stop the machine when animals enter the danger zone.

you have obviously never worked with chooks before !

..I'd still make it slower and run it during the day..If it covers its length every hour,..

Hmm ..??...thats some gearing reduction !


suggestion ... consider a windshield wiper motor.
already geared low,.. lots of torque,...simple to drive ( solenoids) ,..ready made "timer" systems are available. !

[liveforphysics]

You need under 0.1hp.

You need a 50w system, and proper gearing to give best result.

Remember, even 1watt can make a 400lbs box climb VERTICALLY the distance you wish to travel over the course of a day.


Doing it right will use very little additional resources over a normal chicken coup, and I think it's neat to spread the feces over a wider area and have it move itself.

You want a pair of 1000:1 planetary gear boxes, a couple tiny little motors (the type hardly matters, pick something sealed, brushless, and easy to control if you want years of no-maintenance), and some big stupid farm equipment wheels that won't get stuck.

[mr.electric]

I have a few of these 500amp contactors I could sell you super cheap to get the project going.
http://item.mobileweb.ebay.com/viewitem ... 7734716578
A redesign based on a smaller gear motor would be best but since it is a group project you will have to argue with the rest of the group and waste plenty of energy debating the pros and cons of a new design.

[liveforphysics]

I have a few of these 500amp contactors I could sell you super cheap to get the project going.
http://item.mobileweb.ebay.com/viewitem ... 7734716578
A redesign based on a smaller gear motor would be best but since it is a group project you will have to argue with the rest of the group and waste plenty of energy debating the pros and cons of a new design.

He doesn't need 5 amps to move that chicken house around at sub-walking speeds.

[mr.electric]

Of course he doesn't need 500 amps