Is there anything that needs to be taken into consideration about drawing too much power from the rover?
I’m experimenting with a pan-and-tilt mount and if I do something aggressive like moving a servo from one extremity to another at full speed, the rover will sometimes turn off (all the blue LEDs go out). If I make a more graceful turn at a more sensible speed, this doesn’t seem to happen. I’ve also had the rover turn off like this when driving it around.
I could make it happen probably about 20% of the time just by using the wasd sample with nothing else attached to the board by going from full-forward to full-reverse.
Does that sound out of the ordinary to you in any way? I’m wondering if the tracks are too tight or if the road and idler wheels are pushed too tightly into the frame…? Too much friction == higher load on the motors? The gearbox is configuration C, as instructed.
Theorising that I was pulling too much power, I’ve made changes to the way the motors are controlled. When the rover changes direction, it now does two things:
1 - It stops for 100ms
2 - It builds up the speed of the tracks slowly, from a value of about 120 all the way to 255 (or whatever the target speed is). 120 was the minimum value I could use and actually have the tracks turn.
I’ve taken a similar approach with the servos on the pan/tilt mount, and it seems to have cured the issue.
I think I remember reading in the rover manual that the battery pack voltage is delivered as-is to the motors. Aren’t the supplied motors 3v? Is it OK to pump 6v from the 4AA pack into them?
Not directly - if you keep the load to a minimum, you can power them from the Arduino’s pins (set one of the digital pins to HIGH, the one next to it to LOW and the last to provide the signal. Note however that the current requirements under load far surpass what the Arduino’s pins can provide, so if you want to move any weight, it’s best to play it safe and power the red and black wires separately.
Vin = 3.7V, so it’s too low. You can use the 4xAA battery pack instead of you’d like and not have any trouble. The 3.7V LiPo is ideal for the motors and small electronics (and works great with the onboard LiPo charger). If you use the 4xAA pack, remember to remove the LiPo jumper so the USB does not try to charge the AA batteries.
We offer a few of those as well: robotshop.com/lithium-polymer-battery-packs-1.html
The overall DFRobotShop Rover (two motors, the microcontroller, a pair of servos which consume quite a bit of current) may consume more than the max 1A the packs are rated for.
This means you can use a 6V battery pack for the DC motors and the servos, but you still need to power the logic and the camera, which require at least 250mA. You have two choices: step up from 6V or step down from 9V. Most of the time, the main battery corresponds to the actuators since they tend to draw more current. Ex: robotshop.com/dimension-engineering-de-swadj.html robotshop.com/dimension-voltage-regulator-board-1.html (makes connections easier).
That’s most certainly a power drain issue - the battery cannot discharge at a high enough current for that motion. The suggested battery is only a 3.7V, 1Ah LiPo which can discharge at ~2A. This means whatever you are doing is likely consuming well over 2A and causing the rover to shut down.
Can you send an image of how you have the Rover built? The tracks should be a near perfect fit and not tight. It sounds like you may not have configured the motor in configuration C. The battery needs to be left charged for at least 10 hours before you use it initially. The battery should have no problem at all powering the motors under full load as well as additional sensors etc.
Correct. We have successfully created that exact setup without any issues. Can you check to see that there is nothing blocking or impeding the servos from moving freely? Also, it’s important to note that the servos, albeit small, can consume a LOT of current - moreso than the Arduino pins can provide. This may explain the brown-outs. You need to wire the servo’s V line to the battery as opposed to connecting them to the digital or analog pins.
For a motor, nominal voltage is the “optimal” operating conditions for a motor - providing the best efficiency vs torque output (not necessarily the maximum torque which may not be efficient). For DC motors, manufacturers often provide a nominal voltage and a voltage range (for example 6V nominal and operates “well” between 4.8V and 7.2V). Outside of these specs the motor will likely run, but really inefficiently and the life span will diminish. Nominal voltage for electrical equipment without a voltage range often means the specific voltage at which the equipment operates.
The Tamiya Twin Motor gearbox is 3V nominal, and feeding them at 4.8V is not great (lower efficiency, which translates to a slightly shorter life span). We use these motors at up to 6V without much issue. For max efficiency, we do sell 4.5V nominal motors as well which can replace the two DC motors in the gearbox.
What’s the voltage range that the servos included with the Dagu pan/tilt kit will work with? Will they work with the 3.7v from the battery? If so, can I attach my servos to the Vin pin?
