Need Advice on Battery for 2 12V 100 RPM DC Gear Motors

Hello, I am an engineering student working on a team based project. I am seeking knowledge on selecting the right battery to run a system with the following components:

Arduino Uno
Vellman VMA03 motor-shield
2 DC Geared Motors - 12V 100RPM by DFRobot

All together the box weighs 1.1 kg or 2.425 lbs with out any batteries.

In a recent test, our team hooked up a bench power supply to the rear motor. The single motor drew 0.2 A with no load and 0.6 A with a load. Our test successfully rotated the rear axel and was able to pick the aft end of the box off of the ground.

Our team theorized that we need approximately 0.6 + 0.6 = 1.2 A to successfully run both motors in tandem under load.

I need to find a battery that can produce 12V and 1.2 A in the smallest weight possible.

If the battery is rechargeable that is a bonus. If the battery can fit and ride in the box that is better.

Our end goal is to turn both motors at the same rpm, rotate all 4 “feet” together, to lift and push the box forward in straight line.

Thank you,

Henry





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You have not said how long the motors need to run on a single charge - that will determine the capacity of the batteries needed.

A pack of 10 x AA NiMh rechargeable cells will give to 12v but maybe not much run-time.

A 3S LiPo pack will give about 11 v and and a 4S pack will give about 15v. The batteries will probably be considerably smaller for a given capacity but a proper LiPo charger is essential if you don’t want to have a fire. The Hobby King website has a wide range of LiPo cells - and chargers.

…R

Thank you Robin for the quick response.

Images displayed now.

Motors need to run long enough for the robot to travel 10 feet for the final test - I’d estimate less than 30 seconds. We haven’t been able to test the “feet” properly due to our failure to provide both motors with the appropriate current on a regular basis.

We can use an external power source if smaller batteries aren’t feasible. We have tried 9V’s, but couldn’t get a strong enough current for both motors to run at the same time under load.

I’ll look into the LiPo pack on the Hobby King website, new website to me.

-Henry

jhenrycooper:
We have tried 9V's, but couldn't get a strong enough current for both motors to run at the same time under load

I suspect you mean the small PP3 style smoke alarm batteries. They are completely useless for motors as they can't provide enough current. If you think 9v would be sufficient then a pack of 6 x AA alkaline cells (9v) or 8 AA NiMh cells (9.6v) should be fine.

...R

Hey Robin,

9V's were the first batteries that we tried since that is what we had sitting around the house. Yes, we did discover that they were not able to deliver enough current.

I do think we need to get as close to 12 V as possible for motor efficiency.

We are looking at a Lipo batteries, am I correct in this thinking,

We need a 3S (3 Cell) to get 11.1 V, which is close to 12 V.

If the 3S has a constant discharge of 20C and a 1000 mAh,

1000 mAh X 20 C = 20000 mA (milliamps) or 20 A maximum discharge current.

If our system only requires 1.2 A, it would it would only pull 1.2 A from the battery, meaning we would not be running at the batteries maximum discharge current. Further, even though this battery has a larger discharge current potential than we need, the extra unused amps would not hurt the rest of the system.

Still learning the basics here...

Thank you,

Henry

jhenrycooper:
If our system only requires 1.2 A, it would it would only pull 1.2 A from the battery, meaning we would not be running at the batteries maximum discharge current.

Yes

Further, even though this battery has a larger discharge current potential than we need, the extra unused amps would not hurt the rest of the system.

They "unused amps" can't do any damage - they will remain inside the battery.

If you are drawing current at 20C the battery would be discharged in 3 minutes (1000mAh means 1 amp for 1 hour or 20 amps for 1/20th of an hour). With your 1.2amp draw the battery should (in theory) last for 50 minutes. But don't be surprised if it runs out in 25 minutes - battery capacity is often dreamed up by the marketing guys.

...R