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I am currently building a line-following robot for a competition this summer. I have figured out everything except the power.

I expect my robot to draw 7.5 amps in the worst case. now, I've selected a 2S LiPo battery for this, as 7.4 volts is enough for my system. However, I am not sure which capacity to select:

  • 300 mAh is more compact, but gives about 2.5 minutes battery life under full load. The course should be covered by my robot in much less than a minute, so from the first glance it is not a problem. However, the battery will need more recharging.
  • 1000 mAh and above give much more battery life, which means more recharging, but they are less compact, which is not particularly good.

I fear that the low-capacity batteries will experience quicker voltage drops, which will decrease performance of the robot. In your poinion, which is the better option regarding the batteries?

Thanks for your time!

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  • \$\begingroup\$ 7.5A from a 300 mAh pack is asking quite a lot. I would go with 1000 mAh, if not more. Maybe you could use two 18650 cells, since they are pretty easy to find.' \$\endgroup\$
    – user57037
    Commented Mar 12, 2017 at 21:46
  • \$\begingroup\$ @mkeith I was looking at a pack like this, since it is much easier to place on my robot \$\endgroup\$
    – Mu3
    Commented Mar 12, 2017 at 21:51
  • \$\begingroup\$ That is a an RC (radio control) type battery. That is probably a good choice for your application. One other thing to remember is that the batteries take much longer to charge than to discharge. If you choose a 300 mAh battery, it may only allow one or two runs, and then require recharging. This could make the development and test process very inefficient. Also, I believe it is common practice to take a lot of safety precautions with RC batteries during charge and storage. Make sure you are familiar with that. \$\endgroup\$
    – user57037
    Commented Mar 12, 2017 at 22:02
  • \$\begingroup\$ What is the motor DCR? it should be >> ESR of battery including end of charge \$\endgroup\$
    – D.A.S.
    Commented Mar 12, 2017 at 22:15

2 Answers 2

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It depends on your robot and the competition.
If speed is part of the competition, you are much better going for the 300 mAH unit. It's likely that the 300 mAH battery will weigh in at about 20g or less and the 1000 mAH at 60g or more. Carrying 3 times the weight will impact your speed and potentially balance. Most Quadcopter Li-po 300 mAH packs are rated to 30C so should be adequate for your purpose.
Having a fully charged battery for each run you compete in is good practice ...if you get three runs, have 3 * 300 mAH packs.

Arrange the plugs on your robot to allow two batteries in parallel, and do your tuning and software updates using a large (5000 mAH) battery on longer leads (or you can connect a battery charger). When you are ready for competition simply plug in your 300 mAH in parallel to the big one.....unplug the big one just before you are ready to run.

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i would go with the 1000 mAh. batteries never work efficiently as they should.you have to expect less than the manual says with batteries that is a thing i knew by experience

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