Comments by Kevin

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 3 January 2017

    Hi, Sean J.

    To expand on Jan's reply: regardless of the absolute numbers involved, the math does stay the same for the relationship between your discharge rate and how long the battery will last, given a specific battery capacity. However, it is important to note that real-world batteries often don't exhibit ideal behavior: increasing the current drawn from a battery usually decreases its effective capacity (the amount of energy it can provide).

    Lead-acid batteries usually have their capacity specified based on a 20-hour discharge period (0.05C discharge rate), as J. Lumsden mentioned in the first comment here. In your case, the discharge rate is more like 1C. Looking at this graph, you should probably only expect to get about 2/3 of the battery's 18 Ah rated capacity at that discharge rate, or about 11-12 Ah.

    That seems like it would be marginally okay for your application (11 Ah / 18 A = ~0.6 hours), but you might consider using a larger battery to be on the safe side, especially if you want to keep the battery from discharging to too low of a level (which could shorten its lifespan). On that note, you should also ensure that you use a deep-cycle battery that is designed to be discharged down a substantial portion of its capacity.


  • R2-DR, Kevin's dead reckoning robot

    R2-DR, Kevin's dead reckoning robot

    - 8 March 2016

    Hi, Jordi.

    To clarify, I have not made the plans or design files for my robot available. I used some drawings from the R2-D2 Builders Club when designing my robot to make it match the shapes and proportions of the real R2-D2. It's been a while and I don't remember all of the exact drawings I used, but I think I found the ones in "Files > 002-OFFICIAL_BLUEPRINTS > OUTLINE DRAWINGS" to be the most useful.

    - Kevin

  • New product: LPS25H pressure/altitude sensor carrier

    New product: LPS25H pressure/altitude sensor carrier

    - 26 November 2014

    Hi, Jeff.

    The data for this comparison was taken with a sampling rate of 12.5 Hz for both sensors and all other settings left at their power-on defaults (except for additionally enabling the hardware moving average for some tests); see the enableDefault() function here:

    - Kevin

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 12 March 2014

    The capacity of any particular battery also depends on several things other than its size, including its chemistry and manufacturer, but this Wikipedia article lists some typical capacities for common sizes:

    - Kevin

  • Continuous-rotation servos and multi-turn servos

    Continuous-rotation servos and multi-turn servos

    - 9 August 2012

    Hi, David.

    We don't know of any specific considerations with digital servos, but I think it's going to depend on the particular model of servo, and we haven't tried modifying that one. You should get a pretty good idea of whether it will be practical as soon as you open it up.

    - Kevin (engineer at Pololu)

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