# PaulMakesThings

PaulMakesThings
225
I am a robotic engineer, and I like to make things and teach others.

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• There's no special trick to that. I just found a screw that was the right size for the idler to spin on and the right length to go through and into the plastic on the other side, but not too far to avoid going into the gears. Then I drilled a small hole in the case and attached the wheel with it.

• What Arduno and servos are you using? The batteries need a voltage that is sufficient for either the regulated or unregulated input on your arduino, and for your servos. And they need to have enough current to power both the servos. There could be quite a range of current on the servo, a 9g servo could draw 200-300 mA free running, and up to 700 mA when stalled, maybe a bit more. Without the motor torque constant (Kt) or velocity constant (Kv), or any info about your build I can only guess. Mine draws about 420 mA when driving full speed in a straight line on my desk. If you have the servos you want to use the best way to be sure of current need is to test it.Once you have that info, pick a battery with a maximum continuous discharge current that is high enough. This may also be listed ...see more »What Arduno and servos are you using? The batteries need a voltage that is sufficient for either the regulated or unregulated input on your arduino, and for your servos. And they need to have enough current to power both the servos. There could be quite a range of current on the servo, a 9g servo could draw 200-300 mA free running, and up to 700 mA when stalled, maybe a bit more. Without the motor torque constant (Kt) or velocity constant (Kv), or any info about your build I can only guess. Mine draws about 420 mA when driving full speed in a straight line on my desk. If you have the servos you want to use the best way to be sure of current need is to test it.Once you have that info, pick a battery with a maximum continuous discharge current that is high enough. This may also be listed as a C rating. 1C means the discharge rate is the capacity of the battery in unit/hours divided by hours times the rate, which is 1 in this case. That makes it sound complicated but for example, if you have a 240 mAh battery drop the h and multiply it by the C number.240 mAh with 2C means you can draw 480 mA1.8 Ah with 3C means 5.4 A2400 mAh 30C means 72,000 mA or 72 AYou get the idea.

According to the page for the Arduino Nanohttps://www.arduino.cc/en/Main/arduinoBoardNanoIts input voltage is 7-12 V, but it also says "operating voltage 5 V" I can see how this would seem a bit confusing. The 5V is what it gets after the regulator, the 7-12 V is what it can take if it goes through the regulator. At the USB connection, you don't want to exceed 5V. But the pin Vin goes into the 5 V regulator, which will cut down voltages 7-12 V to 5 V so they can power the microcontroller and other components.See this schematic:http://download.arduino.org/products/NANO/Arduino%...In short, connect 7.4V to Vin and the negative battery lead to a ground pin and you'll be fine. Just don't connect it to the 5V pin, that pin is connected to the 5 V rails after the regulator and anyth...see more »According to the page for the Arduino Nanohttps://www.arduino.cc/en/Main/arduinoBoardNanoIts input voltage is 7-12 V, but it also says "operating voltage 5 V" I can see how this would seem a bit confusing. The 5V is what it gets after the regulator, the 7-12 V is what it can take if it goes through the regulator. At the USB connection, you don't want to exceed 5V. But the pin Vin goes into the 5 V regulator, which will cut down voltages 7-12 V to 5 V so they can power the microcontroller and other components.See this schematic:http://download.arduino.org/products/NANO/Arduino%...In short, connect 7.4V to Vin and the negative battery lead to a ground pin and you'll be fine. Just don't connect it to the 5V pin, that pin is connected to the 5 V rails after the regulator and anything much over 5 V will probably fry something. As a side note, this device is not tolerant at all of reverse voltage, make sure you connect battery + to Vin and battery - to Gnd, do it backwards for even a moment and the Arduino will be busted.

What Arduno and servos are you using? The batteries need a voltage that is sufficient for either the regulated or unregulated input on your arduino, and for your servos. And they need to have enough current to power both the servos. There could be quite a range of current on the servo, a 9g servo could draw 200-300 mA free running, and up to 700 mA when stalled, maybe a bit more. Without the motor torque constant (Kt) or velocity constant (Kv), or any info about your build I can only guess. Mine draws about 420 mA when driving full speed in a straight line on my desk. If you have the servos you want to use the best way to be sure of current need is to test it.Once you have that info, pick a battery with a maximum continuous discharge current that is high enough. This may also be listed ...see more »What Arduno and servos are you using? The batteries need a voltage that is sufficient for either the regulated or unregulated input on your arduino, and for your servos. And they need to have enough current to power both the servos. There could be quite a range of current on the servo, a 9g servo could draw 200-300 mA free running, and up to 700 mA when stalled, maybe a bit more. Without the motor torque constant (Kt) or velocity constant (Kv), or any info about your build I can only guess. Mine draws about 420 mA when driving full speed in a straight line on my desk. If you have the servos you want to use the best way to be sure of current need is to test it.Once you have that info, pick a battery with a maximum continuous discharge current that is high enough. This may also be listed as a C rating. 1C means the discharge rate is the capacity of the battery in unit/hours divided by hours times the rate, which is 1 in this case. That makes it sound complicated but for example, if you have a 240 mAh battery drop the h and multiply it by the C number.240 mAh with 2C means you can draw 480 mA1.8 mAh with 3C means 5.4 A2400 mAh 30C means 72 AYou get the idea.

• PaulMakesThings commented on PaulMakesThings's instructable Arduino Nano based Microbot5 months ago

I don't think gator clips are required for any of these steps, also, I didn't make a tool list. This only requires basic electronics tools like wire cutters, pliers, a soldering iron, and a small screwdriver.

Right.

• PaulMakesThings commented on PaulMakesThings's instructable Arduino Nano based Microbot5 months ago

That capacity will be enough, but many small LiPo batteries are 3.7V, and some arduino boards are 5V. If you have one that runs on 3.3 then a 3.7V cell should be fine. If it has a 5V regulator it might not power on.

• PaulMakesThings commented on PaulMakesThings's instructable Arduino Nano based Microbot6 months ago

It will work with a wide range of values, it's just working as a voltage divider to give the servo control IC a reference voltage that is right in the middle. In this case since the positive voltage is 5V and the other end is ground (0V) and the two resistors are equal, you get 2.5V.The servo usually works by comparing the potentiometer voltage to the target voltage and setting the speed proportional to the difference, so that the further it is from the target position the faster it will move, and it will stop when it gets there. By setting the feedback voltage fixed in the middle of the range it moves at a speed which is proportional to the target voltage minus the middle voltage, so that it stops when it gets a neutral signal and runs faster in one direction or the other depending on ...see more »It will work with a wide range of values, it's just working as a voltage divider to give the servo control IC a reference voltage that is right in the middle. In this case since the positive voltage is 5V and the other end is ground (0V) and the two resistors are equal, you get 2.5V.The servo usually works by comparing the potentiometer voltage to the target voltage and setting the speed proportional to the difference, so that the further it is from the target position the faster it will move, and it will stop when it gets there. By setting the feedback voltage fixed in the middle of the range it moves at a speed which is proportional to the target voltage minus the middle voltage, so that it stops when it gets a neutral signal and runs faster in one direction or the other depending on the command.But more to your question, any values that match eachother will work so long as they aren't so low that they effectively short out the controller (if you used say 7 ohms the power would all go through your resistors and the system would shut down) or so high that the reference voltage is undetectable. So anything from 2k to 1M should work, maybe even outside that range.

• PaulMakesThings commented on PaulMakesThings's instructable Arduino Nano based Microbot6 months ago

Thanks!