Hi-
Ive constructed and programmed a mini (10cm) quad copter. Right now im running into an issue with driving the motors. I want to use a transistor to drive them PWM style, But I cant find a transistor to sink ~600-700mA at 3.7V (Signal pin is 3.3V). Does anyone know of a transistor that fits my requirements (and is very small), or some alternative?
-Nick
Hi, your best bet is to look for N-ch Mosfet to do the PWM driving, transistors will drop a relatively high voltage compared to your supply volts so little will get to the motor, a.so because of the current requirements you will have a heat loss problem.
You need to check out the arduino Main Site and look at how to drive a motor with a MOSFET.
Your Mosfet will also have to have low gate voltage characteristics.
Tom.
Well I actually did try Using a mosfet. I used the SI2302... which I thought would have worked, but it did not.
-Nick
N314:
Well I actually did try Using a mosfet. I used the SI2302... which I thought would have worked, but it did not.
I would have used http://uk.farnell.com/taiwan-semiconductor/tsm2314cx/mosfet-n-ch-20v-4-9a-sot23/dp/1864589, however SI2302 should be OK. How did you have it connected? Did you include a flyback diode across the motor?
When i tested it I just hooked up the motor, battery, and SI2302. Vcc to Colloctor and base, emmiter to one lead on the motor. Is there another way I could hook it up to make it more effective?
-Nick
SI2302 is a mosfet so it doesn't have emitter, base or collector. It has source, gate drain, marked SGD on the datasheet at http://www.vishay.com/docs/70628/70628.pdf. Connect it like this:
Also connect a flyback diode in parallel with the motor.
Ok I hooked it up as you instructed, except hooking what would be the signal pin to a pot. Im still not getting the full current. At full power (straight from the battery) I get 18g of thrust, at full power with the SI2302 im getting only 10g.
-Nick
You should get full power. Can you post your Arduino sketch, and a a photo of your wiring?
Vgs too low for full current?
Right now im using a pot, but in the end i will just do a PWM contol of the gate (analogWrite).
Here is my circuit, but i am not getting the same power as the motor hooked directly to the battery.
-Nick
The image in your post appears to be embedded in an email, and as such, it isn't visible.
Hmmm... Sorry. Here:
-Nick
With that circuit, you risk burning out the mosfet when the pot is turned up high enough for the mosfet to be partly on, but not high enough for it to be fully on. Connect the gate to either ground (off) or Vcc (on), not somewhere in between. Make sure Vcc is at least 2.5V. Also remember that mosfets can be damaged by static electricity until both the gate and the source are appropriately connected.
Ok, well even when I remove the Pot, and connect the gate to Vcc or ground, I still do not get full power. On the arduino the gate would get a PWM at 3.3V, which is over what you said... but here im giving the gate 3.7V and its still not giving it full power... why?
-Nick
Is the motor off when you connect the gate to ground, and on when you connect it to Vcc?
Are you certain that the motor needs only 700mA? What is its DC resistance?
-Nick
My guess is that you have a missing ground connection, or a bad connection somewhere.
When the mosfet is turned on and the motor is running (at below full speed you say), what voltage does your meter read between the source and drain? Does the motor speed up if you short the source and drain together right at the mosfet terminals?