Some Success Please forgive my horrendous mess! ! just a test servo what I had lying about . I just need to set up the servo positions at Temp. also my serial is scrolling on the LCD if you look close I need to sort that too.
I'm struggling with trying to account for all of the failure scenarios without it become a massive over complicated beast. There is something beautiful in engineering simple solutions, but in this case we may have to go down the modern bloated multiple redundancy error check route as I do not want to suggest something that may cause overheating and damage to anyone's engine.
Cheers got a few like this cheap china jobbies . could something be run along side a save my bug temp stick ? that's another input . or if you get an over temp cut power to the servo and the flap spring tension will return it to a full open position ?
All stats taken from http://ww.ratwell.com/technical/Thermostats.html A new thermostat is about 35mm long when it hits its target temperature 85C it measures about 46mm long and continues to expand until it's 55mm long. So assuming a linear expansion (it uses a liquid that turns to gas when heated) of 1mm per degree the actual temp operating range is 0 to 74C = 35mm up to 84C = 45mm (closed) 85C = 46mm starts to open 94C = 55mm fully open So if we make things easy for ourselves and assume the servo arm is 57mm from centre to cable attachment then 1 degree of movement will equal 1mm of travel Circumference = 2πr = πd Degree = C/360 Then we need 10 degrees of movement to operate the cable fully
Ok so really i need to settle on what size servo/radius arm. I have also been looking at some linier actuators on the robotshop.com but the prices are close to a new thermostat. What i like about the linier actuators is the tolerance for loading them with force (the sprung flaps ) is pretty high
There are some pretty hefty cheap servos about, you could also try something like this http://www.ebay.co.uk/itm/BOSCH-12-...ED-CAR-HEATER-CONTROL-MOTOR-NEW-/221845073269 but I don't know how easy it would be to control.
Hmm intresting Part looks like a potentiometer and motor in there shouldent ve too bad . resistance would take the place of a rotary encoder for position feed back . Might make a usefull failsafe position sensor .
mechanically that motor you sent looks good . I'm not so good at the sketch writing but what we need is a Arduino running a motor shield / H bridge motor controller the we read the resistance on the Pot and move the motor forwards or reverse like this (http://www.instructables.com/id/Arduino-DC-motor-speed-control-potentiometer/ ) we then need to need to map the 0 to 10K potentiometer to the ds18b20 values . I like the digital temp sensors they work or they don't no dodgy un calibrated readings .
Here's a h bridge tutorial http://www.instructables.com/id/Arduino-Modules-L298N-Dual-H-Bridge-Motor-Controll/?ALLSTEPS this shield only costs a couple of pounds
Got most of it now, I'll have to use a little servo (I have a 15kg rated one on order) but I have the probe and servo bridge now. I have also ordered a laser thermostat to try out if I can find some code for it. I'll knock something up tomorrow and let you know how it goes.
Got everything working except the servo positioning feedback. May need to use an additional pot, unless I modify the existing one built into the servo or use an analogue servo.
I have a cunning plan (as soon as the servo turns up) it involves attaching 2 wires to the potentiometer that's built into the servo and taking the reading from that.
ah I thought it was that one you mentioned was broken . that servo should be perfect then . the worm gear will help with the constant load issue a normal servo would face chattering and wearing out . be sure to share your sketch
