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Thread: On the subject on POWER!

  1. #1
    willcaddy's Avatar
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    Hey everyone,

    I have a few questions about the electrical side of things with my robot that I am building (sorry total noob!) and although I have found some excellent information on the forum, I would like to get some of your opinions for my own specific circumstances if that's OK?

    Firstly, After looking at a few posts i noticed a good few recommendations for running a robot on 24v if you intend to put a motorised axe on it (which I do!). Potentially a nooby question but I have read the spec of my motors and they are able to run at 24V (18V Drill motors) but is it OK to run the whole robot off of 24V with the intention of adding the axe to it at a later date? and how long would be a safe run time whilst over vaulting?

    Secondly, I am intending on using a LiPo battery for the bot under the recommendation of a few people. Would you have any recommendations for brand/model of battery and charger? I have been looking at the Turnigy ones as well as the Turnigy Accucel-6. Also based upon the question above weather its 18V or 24V.

    Finally, I have looked at a good few tutorials now and I'm a little confused as to the best method of working out what thickness/gauge wire I would need to run this off of. The RoboWars Australia videos suggest 12-10 Gauge but I have read on the forum that many use 14 gauge. I have been looking at getting **this** as a starting point. I have also got **these** XT-60 connectors in mind. Can anyone shed some light?

    Again, thank you all for being so awesome and helping this noob out! It is very much apprenticed!

    Will

  2. #2
    overkill's Avatar
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    Running 18V drills on 24V (actually 22.2V for Lipo batteries) is fine, its what most builders do. The motors are likely to get quite hot if you drive the bot hard for three minutes but unless the motors are particularly low quality, the ywill be fine.

    Many UK builders like the Optipower batteries and there is some sort of discount for FRA members. I have used the Hobbyking Nanotech batteries for 4 years with zero problems but some other HK battery brands are not so good. You can get an idea of battery quality at HK just by comparing prices; for equivalent spec packs, the cheaper one will almost always be lower quality in some way. All lipo chargers will charge a range battery voltages up to a listed maximum.

    A 22.2V lipo has six cells in it (usually abbreviated to just '6S'), so a charger that will work with up to 6S packs is what you want - it will also charge lower voltage packs if you need that in the future.

    For wire gauge, think of the wiring loom as a tree with the batteries at the roots and the motors and other parts as the leaves. Start out with thicker trunk wiring and then thinner branch wiring to the motors. In your case, I'd recommend 10g from the battery to the fuse, power link and up to a main distribution point. From there 12g to the axe motor and14g to the drill motors. Using thicker wire isn't bad, it just weighs more and takes up more room.

  3. #3
    willcaddy's Avatar
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    Thanks Overkill for the reply!

    That's really helped! Just one thing, what would you recommend for a switch? I looked at the Botbitz fingertech screw switch but there only rated for 40 amps. Would that be enough for a 24v robot? Would you have any recommendations for UK equivalents? I know in the UK tpunaments you are required to have a link and a switch.

    Thanks again!

    Will

  4. #4
    Garfie489's Avatar
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    Rory from Team Nuts makes the best switches.

    Their the smallest, and quite cheap - whilst also in my experience having the highest ratings. After testing several brands (and blowing them up), Rorys switches are the only thing i found that meets Dystopias slightly higher demands.
    My 3 loves - Rugby, Racing, and Robotics.

  5. #5
    overkill's Avatar
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    All my bots have passed UK tech inspections with just a removable link and no switch, so unless some events are using modified FRA rules, you don't need a switch. You DO however need a fuse on the main power line that is rated for less than the maximum current that the battery is capable of.

    I use an XT90 plug for the removable link and all the similar R/C plugs will do the same job. I like the XT series connectors as they have a shroud around the pins that helps prevent the connector coming apart during impacts and their blocky shape is easy to glue into a home made base.

  6. #6
    willcaddy's Avatar
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    Awesome! Thanks a lot!

    I shall get a xt90 and a fuse set up! This might be a dumb question so bare with me ha ha, but do you specifically have to have DC fuse or will any fuse rated for a certain amount of amps do fine?

    Again thanks for your time and knowledge!

    Will

  7. #7
    overkill's Avatar
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    Virtually any fuse will be fine ,its the current rating that is important. That said, 'midi fuses' meant for cars & boats are popular and easy to use.



    This type is available in a wider range of current ratings and you can buy commercial bases for them or easily make your own. The smaller blade fuses for cars are also OK but have lower ratings not really suitable for spinners.

  8. #8
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    Is the amperage independent of the voltage ?

  9. #9
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    Worth reading through the FRA rules for guidance on fuse rating
    The fuse rating is set by the discharge current of the batteries. You need to understand that and rate the fuse under it

    e.g. (from wiki but google does the job)

    For a 2000 mAh battery with a 15C rating, the continuous current that may be drawn out of the battery is 2000 mAh x 15 = 30000 mA, or 30 Amps (A) (divide by 1000).

  10. #10
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    Also worth mentioning that the fuse should be rated below the burst current, not continuous. So if the above 15C pack had a burst rating of 45C, then the fuse would have to be rated below 90A (45C x 2.0Ah)
    Jamie McHarg
    RogueTwo Robots
    http://www.rogue-two-robots.vze.com

    With great power, comes great reliability.

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