Will this TinyCircuit dual motor driver circuit be able to work with these 2 solenoids and 2 motors?

[ClassicalApple]

Hi, I posted before a while back, and after some people pointed how to ask a proper question (Thank you @dorke and @Harald Kapp), I took their advice and am back again.

From my last post: "I'm trying to create a control system for a rocket. I know, it's a big task. But basically all I have to do is set up a TinyCircuit to pull the pin on two solenoids at 750 feet up in the air which I have successfully simulated by getting a buzzer to beep after traveling 10 feet up my stairs. This will deploy the two parachutes and hopefully turn the rocket around where it will then be controlled by two motors attached to the respective shroud lines in order to control the descent."

I came up with this basic circuit that is intended to use the DualMotor TinyShield to drive two motors and two solenoids (6V) using a 11.1 V 3 Cell LiPo Battery. I understand that the solenoids could be driven with MOSFETS, but I feel like the wiring would be much simpler with the DualMotor. The motors and solenoids will never be running at the same time. With my basic understanding, the solenoids should draw .33 Amps because they are rated at 2 Watts and I am getting the 6V model. And the motors can each draw a maximum of .7 A. This should work because the DualMotor can output a max of 1.8 Amps at each output, right? However, in my current circuit design the voltage across them would be 11.1 volts, because they are in parallel. I have to decrease the voltage right? I was looking at linear voltage regulators and this L78 (6V output, 1.5 A max) seemed to fit what I wanted. If I put them into the circuit before the current splits into the two motors or the two solenoids, but after the motor driver, would that work? In all of this, the part that confuses me the most is the internal structure of the DualMotor. I look at this schematic and my head just explodes. There is an H-Bridge and some MOSFETS integrated within it, but is this enough? Do I just connect everything as shown in my circuit diagram and that is it?

Thank you for any help. <3

 

[Colin Mitchell]

You are much better-off to use a 2gram linear actuator that consumes 30mA @ 3v and is fully reliable.

http://www.ebay.com/itm/1pcs-1-5g-s...269246?hash=item3aada362fe:g:i4YAAOSwu4BVnclM

 

[(*steve*)]

Assuming the motor driver can pass the current required, and your battery can also provide the current, the answer is yes.

However, I would advise you to isolate the power supply to your logic. This can be done simply with a diode and a capacitor. It will help ensure that you don't get a glitch which resets your microcontroller as you fire your parachute release.

Colin's point above is worth thinking about. If you can get away with something that requires less current (why 2 motors and 2 solenoids?) then you can also get away with smaller and lighter batteries.

Another thing you might want to consider is rather than firing the parachute at a specific height, you could take a reading (say) every 1/2 a sec and fire the parachute when you have three readings in a row indicating you are descending. You might also want to consider the device arming itself only when it detects it is some height above it's start height. That way it won't go off before launch.

 

[ClassicalApple]

Wow, thanks for the tip Steve. That would be tragic, I'll make sure to do that. And in regards to your comment about firing the parachute while it's descending: while that is a good idea, the rocket is actually going to preemptively fire the parachutes AS it is going up so that it turns around at its target height.

What are the advantages in using the linear actuators? To me it seems like they wouldn't provide enough force (I can't find how big the radius is) effectively real in the shroud line(s).

But I agree, the 11.1V LiPo is a bit overkill as it would pose a greater overheating risk, I believe.

 

[(*steve*)]

I'm not sure a chute will turn a rocket around. It's more likely to get tangled in it if you release it while the motor is still burning -- or will the motor have burned out by then?

As for what can control the shroud lines, my guess is that you will be pulling against some fraction of the rocket's weight. How far do you need to pull them, and how fast?

Have you thought of popping out some wings and flying it down? (probably a silly idea)

 

[ClassicalApple]

Yeah the motor will have burned out and the parachutes will stop it. There's plenty of time to fall to the ground, so the motor speed is not THAT important, as long as it holds.

And as for that plane thing, maybe next time haha.