Automatically actuated grill block - Mk3

[Daox]

I just started looking the the arduino servo library the other day. However, it seems very easy to use. First, you setup a servo in the code. Then, at any point you can tell the servo to go to X degrees. Its really that simple. Here is an example code that moves a servo based off input from a potentiometer. My code will be very similar, except that it'll fully open or close the block based off of the temperature of the coolant. At this point I don't plan on partially opening the grill block.

https://www.arduino.cc/en/Tutorial/Knob

/*
 Controlling a servo position using a potentiometer (variable resistor)
 by Michal Rinott <http://people.interaction-ivrea.it/m.rinott>

 modified on 8 Nov 2013
 by Scott Fitzgerald
 http://www.arduino.cc/en/Tutorial/Knob
*/

#include <Servo.h>

Servo myservo;  // create servo object to control a servo

int potpin = 0;  // analog pin used to connect the potentiometer
int val;    // variable to read the value from the analog pin

void setup() {
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
}

void loop() {
  val = analogRead(potpin);            // reads the value of the potentiometer (value between 0 and 1023)
  val = map(val, 0, 1023, 0, 180);     // scale it to use it with the servo (value between 0 and 180)
  myservo.write(val);                  // sets the servo position according to the scaled value
  delay(15);                           // waits for the servo to get there
}

Once I get done with the mechanical stuff, I will be moving into the electrical and I will post my code when I get there.

The arduino will be tapping into the coolant temperature sensor signal so it knows when to open and close, but that is about it other than hooking up power and ground wires.

As for powering the servo, it should be able to be run off the 5V power regulator onboard the arduino. The specs on the regulator say it can handle up to 800mA, and the servo specs say it uses 200mA. So, we have plenty of head room for the arduino to do its job.

[RoadCyclist]

A. But how are you powering the Arduino itself? It needs power too!

B. It wouldn't be too hard to divide the servo activation into steps, i.e. 1/2, 3/4, 1/4 open, depending on the input value. Again, I'm no expert here, but that's my opinion based on what little experience I've got.

Thanks for sharing your research, by the way! I really am looking forward to your progress.

[Daox]

The arduino will be powered with 12V switched power from the car. Most versions of the arduino have a power regulator circuit built into them, so it can easily accept 12V input. No filters (capacitors) needed as they're built into the regulator circuit.

Quite true, it would not be too hard to program the servo to open incrementally. However, I don't see much advantage? As I see it, ideal operation is to wait until just before the electric fan turns on, then open the grill block. This ensures the radiator is completely full of the hottest coolant possible. That means our bang for the buck of airflow will be the greatest. I'll drop the coolant temp down to just above where the thermostat closes, and then close the grill again. It will cycle open and closed. I don't think it'll be too often, but testing will tell. If it is actuating too often, adding variable grill block logic would probably be advantageous. If anyone sees flaws in my logic, do tell!

[seifrob]

Good work! It looks like it is drawn in Google SketchUp. Is it?

[Daox]

Thanks seifrob!

The software I use to draw up all my stuff is SolidWorks. I use it professionally daily so its a lot quicker for me to do it in that than Sketchup. I did try Sketchup once. It seemed pretty nice for a free 3d software package. But, since I already know Solidworks, that is what I stick with.

[gumby79]

If you find the micro servo dose not pack enough punch,then consider using a spring for close and setup the servo as a winch. Insted of a larger servo

Winch setup

Opt1 disable the potentiometer (as per instructions below)
Opt2 Relocate the potentiometer to the grill flap (this option would delete the need for limit switches)
-crawler-tech-how-build-winch.html
Gumby Stay Flexible

[Daox]

Interesting idea, thanks Gumby.

[LittleBlackDuck]

Originally Posted by Daox

The arduino will be powered with 12V switched power from the car. Most versions of the arduino have a power regulator circuit built into them, so it can easily accept 12V input. No filters (capacitors) needed as they're built into the regulator circuit.

Quite true, it would not be too hard to program the servo to open incrementally. However, I don't see much advantage? As I see it, ideal operation is to wait until just before the electric fan turns on, then open the grill block. This ensures the radiator is completely full of the hottest coolant possible. That means our bang for the buck of airflow will be the greatest. I'll drop the coolant temp down to just above where the thermostat closes, and then close the grill again. It will cycle open and closed. I don't think it'll be too often, but testing will tell. If it is actuating too often, adding variable grill block logic would probably be advantageous. If anyone sees flaws in my logic, do tell!

A few gotchas for you to watch out for:

The arduino reg generates a lot of heat and may not like extended periods at 14V. Might be better to have a pre-regulator to knock it down to 8-9V and kill more noise too.

By using proportional control of the servo you will prevent cycling and excessive open/close cycles. I would choose an opening amount based on the rate of rise of the coolant temperature and modify this in a closed loop to get equilibrium rather than flopping around like a dying fish between extremes.

You might also consider the cooling fan as an additional input to adjust the strategy - if the fan is running for longer than x minutes then open up more and conversely if it is off for y minutes then close it up a bit.

Ambient temperature should also be used to modulate the opening rate / amount - I would not slam it open if the air temp is -20.

You could also use an analog input connected to a variable resistor to change the reactivity (gain) of the loop for tuning.

Simon

[Daox]

Good point about the 14V. However, the vast majority of the time the servo isn't going to be in use. So, the load will primarily just be the arduino which doesn't really pull much power (~45 mA per a quick google search). However, I will keep an eye on the regulator temp. I'd like to keep this as simple as I can. If it becomes an issue, I'll look into changing it.

I like the idea of closed loop control to create equilibrium. Perhaps that'll be stage 2 once I get it installed and working.

Ideally, I'd also like to come up with a way to close the grill block when the car is shut off. This would help retain some heat in the engine for a bit longer. If anyone has any ideas on that, I'm all ears. I'm not sure how much this would really be super useful though if it takes much more complication to implement.

[Daox]

I've been printing as I've progressed to test out the pieces, but I figured I'd show some of the images with you guys. Its not vaporware, I swear!


Here is the initial blade design. The blade is 1/8" thick here. I later beefed up the pivot point to 3/16" diameter. I think 1/8" would have been fine, but 3/16" will definitely be plenty strong.






This was the test piece for the frame. It is surprisingly sturdy once snapped together. I also tested the blade clip which needed a little tweaking. The snap was a bit too tight. The other clip you see on the far right was for the power door lock actuator mounting piece which has now been eliminated.





These parts were just printed last night. The blade clip is a new design and it works beautifully.





The servo mount also works very nicely as well. There isn't a ton of extra room though! So far I'm really happy with how the design is coming together.