Build a Solar-Tracking Robot

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hoangphat90
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Build a Solar-Tracking Robot

Post by hoangphat90 »

Hello everyone,

I read this
https://www.sciencebuddies.org/science- ... #procedure

and know that we need 2 power sources: one 9V for arduino and one 6V for a motor.

I wonder if we could use 7.4 V for arduino and 7.4V for motor?
cmpayne
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Re: Build a Solar-Tracking Robot

Post by cmpayne »

Dear hoangphat90,

I don't think you can use two 7.4 V power sources as alternatives to the 9 V and 6 V sources if you wire the circuit as shown in the diagram. The Arduino tech specs recommend an input voltage of 7-12 V (https://store.arduino.cc/usa/arduino-uno-rev3), so I suspect the Arduino may not have enough power near the lower limit. You may be able to use the two 7.4 V sources if you wire the two sources in parallel, however.

Either way, you can certainly try it with the 7.4 V sources. If you move the dark red wire on the 5V pin to the Vin pin (on the Arduino), the fuse will blow if you overload it, but I don't think you will. (The FAQ on the Arduino page says the 5V pin bypasses the fuse apparently.)

Sorry I don't have a more definitive answer for you! It's been nearly 20 years since I took the required electrical engineering course for my degree (chemical engineering). I'll see if one of the other experts can weigh in though.

Best of luck!
Dr. Payne
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Re: Build a Solar-Tracking Robot

Post by bfinio »

Hi,

I am the designer for the Bluebot kits, jumping in here. Power supplies are rated both by their voltage and the amount of current they can provide. The Arduino has an on-board voltage regulator which can accept an input between 7-12V as you mentioned, and it brings that down to a regulated 5V. This makes it easier to power the Arduino with a range of voltage supplies. However, it's generally not a good idea to try and run lots of current through the Arduino to power things like motors, which is why we have a separate power supply for the motors (it's OK to do it for just a few LEDs, which is why most introductory "blink an LED" tutorials for Arduino don't have a separate power supply). So, all that being said:

- You should be fine with a 7.4V supply for the Arduino, because it's within that 7-12V range. You shouldn't start running into issues unless you drop below 7V. There is already some "buffer" built in there above the 5V.
- However, I WOULDN'T recommend using a 7.4V supply for the motors. The motors in the kit actually have a suggested voltage of 4.5V, so we are already over-driving them a bit at 6V. 7.4V may risk burning out the motors.

Hope that helps,

Ben
hoangphat90
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Re: Build a Solar-Tracking Robot

Post by hoangphat90 »

cmpayne wrote:Dear hoangphat90,

I don't think you can use two 7.4 V power sources as alternatives to the 9 V and 6 V sources if you wire the circuit as shown in the diagram. The Arduino tech specs recommend an input voltage of 7-12 V (https://store.arduino.cc/usa/arduino-uno-rev3), so I suspect the Arduino may not have enough power near the lower limit. You may be able to use the two 7.4 V sources if you wire the two sources in parallel, however.

Either way, you can certainly try it with the 7.4 V sources. If you move the dark red wire on the 5V pin to the Vin pin (on the Arduino), the fuse will blow if you overload it, but I don't think you will. (The FAQ on the Arduino page says the 5V pin bypasses the fuse apparently.)

Sorry I don't have a more definitive answer for you! It's been nearly 20 years since I took the required electrical engineering course for my degree (chemical engineering). I'll see if one of the other experts can weigh in though.

Best of luck!
Dr. Payne
Thank you. I will try to find it out.
hoangphat90
Posts: 4
Joined: Wed Sep 23, 2020 5:31 pm
Occupation: Teacher

Re: Build a Solar-Tracking Robot

Post by hoangphat90 »

bfinio wrote:Hi,

I am the designer for the Bluebot kits, jumping in here. Power supplies are rated both by their voltage and the amount of current they can provide. The Arduino has an on-board voltage regulator which can accept an input between 7-12V as you mentioned, and it brings that down to a regulated 5V. This makes it easier to power the Arduino with a range of voltage supplies. However, it's generally not a good idea to try and run lots of current through the Arduino to power things like motors, which is why we have a separate power supply for the motors (it's OK to do it for just a few LEDs, which is why most introductory "blink an LED" tutorials for Arduino don't have a separate power supply). So, all that being said:

- You should be fine with a 7.4V supply for the Arduino, because it's within that 7-12V range. You shouldn't start running into issues unless you drop below 7V. There is already some "buffer" built in there above the 5V.
- However, I WOULDN'T recommend using a 7.4V supply for the motors. The motors in the kit actually have a suggested voltage of 4.5V, so we are already over-driving them a bit at 6V. 7.4V may risk burning out the motors.

Hope that helps,

Ben
Thank you for your advice. I am instructing K-8 students in a club to build robots, so I have to try doing before telling them. The money is another problem for me to consider. By the way, my students love the Art Bot which you designed so much.
bfinio
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Re: Build a Solar-Tracking Robot

Post by bfinio »

Happy to help - out of curiosity what voltage supply are you using that's 7.4V? That sounds unusual to me - we typically use 9V batteries or AA batteries which give you multiples of 1.5V.
hoangphat90
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Re: Build a Solar-Tracking Robot

Post by hoangphat90 »

Dear bfinio,

I intend to let students build all your bots in this school year. I live in Vietnam, my school doesn't give me much money. So I think it's better to use rechargeable batteries like this (each cell has 3.7 V):

https://www.amazon.com/NCR18650B-Storag ... 579&sr=8-2

Moreover, after teaching them about breadboard, sensors through Dancing Bot and Motion-activated Robot Lesson, I will use L298n motor driver, because my students (grade 6 and 8) are too young to handle with L293 ic. When searching on the internet, I realized that it's okay to use two 18650 cells for both arduino and motor.
bfinio
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Re: Build a Solar-Tracking Robot

Post by bfinio »

Ah OK, that makes sense. So if you are also buying your own motors and not using the ones in our kit, I would just double check the voltage rating. I doubt 7.4V will damage anything even if it is slightly over the rating, but it's good to be sure.

To clarify about the L298N, are you talking about just using this:

https://www.digikey.com/product-detail/ ... IoQAvD_BwE

or the breakout board with screw terminals?

https://components101.com/modules/l293n ... ver-module

Either way, I'm not sure if that will be any simpler for your students than the L293D, and it looks more expensive. If they are already learning to use a breadboard, then using the L293D is just a matter of carefully following the step-by-step wiring diagram in the project. It looks like you need to make the same number of connections for the L298N. I don't have experience using the L298N though, so whatever makes the most sense for your class!

Please keep us posted on how things go.

Thanks,

Ben
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