There is an upcoming SumoBot competition at our school, 600 grams weight limit. Then ran into a problem. I was using two 9V battery in parallel to power the entire robot, but its current supply was not enough, also no boost converter at this point, total weight at 598 grams. Though my robot can move, it cannot push any object.
So, I plan to change its power source from the two 9 Volts to an 18650 battery with two boost converters. One to supply the motor driver at 12 volts and the other to the Arduino Nano at 7 volts. Total weight at 596 grams. Having two 18650s will surpass the weight limit.
Will this new method of powering my robot viable or not? My main concern is that the high current discharge from the battery that is needed for the motor driver will overflow to the Arduino Nano and frying it.
Nope. The Arduino will only consume exactly much current as it needs, provided you supply it with the correct voltage.
In principle your approach should work, but you should verify if the combined current you're trying to draw from the 18650 is within its specifications, and if this will yield a sufficiently long runtime given the capacity of your 18650.
You could try to save some weight by using a smaller boost converter for the Arduino, and shaving off material off of the construction parts of the bot (wheels, frame). There also seems to be an unused breadboard in the center of the bot that I assume you'll ditch.
I know nothing about sumobots, but I'm surprised that it apparently takes 6 motors to run 2 wheels.
How on earth would that happen? Clearly you do not know how electricity works.
Be careful with that idea boost convertors work to boost the voltage only, at the expense of needing more current. The amount of current you can get at the higher voltage is limited by how many times the initial voltage is boosted. So for 3.8V boosted to 12 V is a boost of over three times. The cheap boost converters you get on ebay will probably not be able to supply very much current.
The specifications are written to be ambiguous, and to put to show the converter in the best light. My experience has been that boosting 5V to 12V results in only about 700mA worth of current. How much current do your motors take?
If you look at the data sheet to this part, found on this website by scrolling down to a link to the data sheet.
You will find that the chip has a minimum input voltage of 5V, so I think that rules out your idea.
You could use only one boost converter and two batteries in series. Then you can power the Arduino nano with the 7.4V of the batteries directly to the Vin pin.
Each battery is about 50grm, if it's still too much try to save weight somewhere.
Will the current not overflow to my Arduino Nano? They are connected in parallel so I suspect that the higher current consumption of the Motor Driver which is around 1.2 Amps will overflow to the Arduino Nano that is only taking at most 40mA. In theory, the battery is drawing at least 1.240 Amps not taking into account the boost converters. Or will the current just branch off into 1.2A and 40mA.
Around 1.2A.
6x TT 130 Gear Motor with stall current of 200mA on each motor.
The battery I will be using is the Samsung 35E with a max continuous discharge rating of 8A, so it is more than enough for the booster and all other components.
No.
There is no such effect. Please be told that, or we can give up now.
As far as I can see there is no difference that and a 18650.
As I said:-
That is the chip in the boost converter only works with a 5V minimum voltage. Those units on ebay that claim they "work" on a lower input voltage are not being truthful.
Something might happen with a lower voltage but work correctly they will not.
Nice. But the same problem occurred to my classmate. Two 18650s in series powering the Arduino Uno and the Tb6612FNG in parallel. The Uno was fried even though it was supplied from the DC Jack, center positive.
Using the Samsung 35E, so it should be more than enough.
The frame material is just sintra board, any shaving is only a reduction of less than a gram. The motors are the heaviest component due to its metal shaft. This can run on only two motors, the 3 motors each wheel is just my strategy increase torque.
But not because something else drew power from the battery. I don't contest that your mate's Arduino went up in flames, but the cause is not what you think it was.
Optimism is a useful trait; cherish it.
But do try to balance it with realism, as well.
You're likely better off selecting two motors with more torque than 6 motors. You're lugging around a lot of dead weight this way and creating additional mechanical challenges.
Yep, it was a huge mistake to stack motors and I am now seeing the repercussions. For gearing the motors, I had no problem so far. The deadweight is a liability.
I'd like to point your attention back to @anon27210439 's suggestion as well. Use two cells in series and lose some weight elsewhere. This will cut the current draw from the cells in half and make the selection of a boost converter less critical.
I hope you have battery protection? To protect your 18650 from over-discharge. That can damage them so that when you try to recharge them, they can explode or catch fire. Most 18650 batteries don't have any protection built-in.
Li-Po battery packs could be an alternative. You can get these in 7.4V and 11.2V and they have protection circuit built-in.
Yep. The TP4056 1S. I plan to attach it to a 1S battery holder so changing to another 18650 is hassle free. I'm only after the over-discharge and over current protection. My Liitokala Lii-S4 will handle the charging.
Take care because TP4056 is a charge controller chip. It does not protect against over-discharge or over-current.
Some boards commonly available on eBay/Ali etc, that use the TP4056, also contain circuits to protect against over-discharge and over-current, but others do not.
i'm worried that the current discharge of the battery that will not be sufficient for the boost converter to provide 12v at (around) 1.3A due to the added protection, over current protection at 3A.
That module should protect the battery ok. Although you could save a tiny bit of weight using a over-discharge/over-current only module, assuming that you don't want to charge the battery in-situ.
