First thing’s first, I’m new to this forum, so I apologize if i posted in the wrong place.
Second, I never used an Arduino board before, so please treat me like a beginner.
I’m worried that a) the shield is not made to fit physically or not compatible electronically the Leonardo and b) that USB won’t be able to supply enough power to the motors. Assuming no/minimum load.
I have now switched my strategy. Instead of a Leonardo, I’m going to use a Arduino Nano.
And instead of high current drawing stepper motors, i’m going to use a Continuous Rotation Servo
Less circuitry, less current requirements, more for both the servo to use right?
And instead of a controller, I’m just going to control the servos directly with a PWM from the Nano
The only concerning point I’m trying to find is how much current can the Nano provide (taking your last concern into consideration). I’ve seen sites saying 500mA, some say 40mA. The servo itself needs 140 with no load, so if it’s 500mA, great! but if it’s 40mA then i might have a problem on my hands.
So suppose I am now loading the servo with something that’s close to it’s torque rating, I would assume that the current drawn would also increase.
But what i’m interested in is by how much? Another way of putting it, how much current is needed to power the servo at its torque rating since the current on the datasheet is given with “no load” conditions
Once again powering via USB, trying to figure out whether or not this setup is feasible or not. Thanks
Here’s what i’m trying to do:
Power a microcontroller with USB while connecting a servo to the microcontroller with direct leads (no controller).
The servo is driving a pinion and rack system, which raises and lowers a “gate”.
The calculated torque required (includes pinion, rack, gate) is around 2kg-cm
The servo has a torque rating of…
which is why I said its operating close to “full load” conditions.
So considering the microcontroller is only running the servo, 500mA - 300mA still gives me a 200mA of wiggle space. Well, it should…right?
Thank you with your help so far Coleman.
I’ve checked digikey and mouser for PTC fuses.
I would like to check definitions with you: Hold Current is a current which a fuse won’t heat up, past that, it’ll heat up a little and after trip current, it’ll heat up a lot. So since the servo’s drawing ~300mA, I would look for a hold current of 300mV (but Ih = 200mA would also be ok yes?)
Looking at MF-PSMF020X-2TR-ND
However, looking at digikey’s and mouser’s PTC resettable fuses, all through hole fuses seems to have a trip time of 2.5s
Considering that i’m dealing with an almost instantaneous current draw (from driving the servo), doesn’t 2.5s seems too slow to trip?
It should be - the Leonardo uses the same pin configuration.
This is dangerous - a USB port can usually supply a maximum of 400-500mA, and the microcontroller itself can consume 100mA of this, leaving only 150-200mA Max for each motor (even with minimum load). More than likely each motor coil needs about this much current, so there’s a good chance you’ll fry the USB port on your computer. Use a battery if you can, but check the specs of the stepper motors.
A simple Arduino microcontroller (even the Nano) can power the continuous rotation servo if it has no (or minimal) load directly from a USB port. HOWEVER, if you stop the servo with your hands and prevent it from turning, there will be a spike in the current and you might fry your USB port.
So when you load it, it may (roughly) double… consuming up to 300mA under full load. There is no load curve for that servo unfortunately. Can you describe your setup a bit more and what you plan to do?
A USB port can handle about 400mA (500mA on some computers). Unfortunately RobotShop does not currently have a selection of fuses, so you might try Digikey or Mouser. You would need a 5V, 500mA fuse (ideally resettable).
Recall that it’s not only the servo which is drawing current - the controller is also consuming ~100mA, so the fuse should be about 400 to 500mA, and anything above that should trip it so there is no damage to the computer. Also, the fuse that you attached looks like it’s surface mount - we suggest one with wires so it’s easier to connect.
