How do I pick a motor and drive mechanism for an automation project?
My immediate need is to drive a pinion which drives a rack which pushes a ~5kg wooden door open on my hen house. The door is hinged at the top, is about 1.2m high, and I need to push the bottom out by about 30cm to allow the chickens egress and ingress. When it is shut I either want the motor to be strong enough while “dead” to prevent a fox prying the door open, or I will add a “keeper” (servo with a bolt on the end of a horn) to lock the rack in place.
I suggest using a 12V DC-Motor and a H-Bridge. I’ve got a popup-headlight from an old toyota with a really gutsy Denso motor and pinion already attached that wouldn’t take much work to adapt I think.
At the moment, I’m working on bluetooth controllers for activating it, and have some H-Bridges to donate that will run at 12v.
I might be able to pop into the Hackerspace this week, just need to plan ahead a bit with which nights will be open.
A similar need: our house has a sliding door that is frequently used, it is now double-glazed and rather heavy. The movement is about 1m. A very inconvenient setup, especially when no hand is free to open it.
I had wondered about adapting a garage-door opener, they have some safety features so should not squash a tiny grandchild.
Any ideas, folks? Have I found a project for my shiny new Arduino?
Sounds interesting. Maybe worth a dedicated discussion/hack session sometime.
I’ve just been working on some Toshiba TA8050 motor controllers. They have overcurrent protection which means they actually turn off if the motor becomes locked if I understand it correctly.
And these work on the arduino too.
The best mechanism that I’ve ever seen for window/door opening is a system with an electric motor with cogs driving a specially made spring of about 1cm diameter. Also found in European car electric windows.
If a residual object becomes lodged (read child-stuck-in-door/window) the spring simply absorbs all force and prevents any splitting/squashing of the said biological object.
I don’t know where you’d buy that here for 1m in Australia. A lower-tech alternative might be to try something with a threaded rod available from the hardware store. The chances of making that work might be about 90%.
Yes, there are commercial door opening solutions available and you definitely pay for what you get.
A simple H-bridge can be made by 2x N-CH fets and 2x P-CH fets, note that
in its simplest form you will have to be exceptionally careful to make sure
the magic smoke doesn’t escape from crowbar-ing the rails
If you add 4x opto-isolators (though slows down the speed it can run at)
you can jig it in such a way that it is impossible to crowbar
Otherwise it works really well (I built one for my tonka bot and it worked
quite well, the optos proved quite effective at avoiding the crowbar), be
sure to over heatsink and to remember to insulate the package from the
heatsink (as many of them have either the output or input pins tied to the
tab)
Sorry if I was a bit late. I can come another time.
Anyway, I did a bit more work on the system and now I have Bluetooth control and it’s running off a 9V battery. If it is to your liking I can donate it to you.
The Bluetooth means that you can log into the device from a PC/Mobile Phone and send commands to it to make it open and close.
I’m thinking to add some software commands to make it Turn On or Off for a set period of time. Like 5-seconds because in a door situation - most of the time that’s what’s needed. I guess another upgrade option would be to have some limit switches. So that the motor can turn off if the switch gets tripped - ie at the end of travel.
You have to consider how heavy the door is, how much pressure is required to overcome the wind, and how quickly you want the door to open. Also, is this hobbyist level scrounge cheap parts only, or is it a serious need to do the job properly project?
Look at Oatley Electronics for used electric motors with matching chains and sprockets for the electric bike fraternity. To aviod killing chooks and small children, consider moving weights rather than the door directly. If you cant find a H-drive easily for this amount of power, consider using a relay.
Look for used commercial garage door opening parts at the recycling depots.
For a real hobbyist solution use a bucket with rope over a pulley attached to the door. To close the door, use a water solenoid from a washing machine to fill the bucket with water.
Now you’ve got me going.
If you had a rope attached to the nesting boxes for the chooks, when all the cooks are in, the weight of the chooks would close the door.
Consider a cat flap - some use a tag on the chook to allow the door to open. I’m not sure if they use an RFID tag ararngement or just a magnet and sensing coil - have a look at the commercial ones. maybe you could teach the chooks to peck at a switch?
