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  1. #1

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    rc electric noobie help needed badly

    hi i just bought a traxxis rustler vxl. I have never owned a elctic car before only nitro. Is there anything i need to do with is before it is ready to bash. ex break in the motor or something. help would be very appreciated thanks alot

  2. #2
    Community Moderators Foxy's Avatar
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    RE: rc electric noobie help needed badly

    Here is a run down of the basics of what you should know about running an electric brushless RC (quote is my own work)...

    You do not need to break it in at all, and since the motor and speed control are a set, you don't need to worry too much about those either, but you do need to be aware of the limitations and types of battery.

    In response for your request concerning info about electric in general, here are some basic guidelines:

    Motor

    Motors come in 2 basic varieties; brushed and brushless. Brushed motors are older technology and are only really used still in classes that dictate you must use a brushed motor, and other applications that require very smooth throttle response and low speed control, such as Crawling and Drifting. Brushed motors need maintenance every so often, changing the brushes when they wear down and sometimes shaving a layer of metal off the commutator (using a 'comm lathe') to provide a better surface for the brushes.

    Brushless motors are the newer technology, requiring no maintenance and delivering significantly more speed and power for the same ratings.

    Both types of motor are rated in 'turns', with higher turns being more torque and less speed, and lower turns the opposite. Most brushless motors are also referred to as having a specific KV rating. This is a measure of their maximum rpm per volt. So, for example, if you see a brushless 10.5 turn 4000kv motor, it will turn 4000rpm for every volt supplied at maximum throttle. So the max speed (in rpm) of that motor on a 7.4v lipo battery will be 7.4*4000. In general consider that 3000kv or less is a fairly slow motor for high torque, and a 9000kv motor is a very fast, less torquey motor. The current a motor pulls on startup and under load (amps) goes up with the KV.

    Speed controllers

    Speed controllers also come in the brushed and brushless variety, indicating what kind of motor they can accept. There are many speed controls which can be switched or switch automatically between brushless and brushed operation. Running the wrong type of speed controller for the motor or running the wrong setting will destroy the speed controller and/or the motor in pretty short order.

    The next things to look at on a speed controller are voltage and current ratings, which must not be exceeded. Often a speed controller (hereafter referred to as an ESC) will say first how many volts you can pump through it. Though this is often expressed in how many cells you can use (the number of cells your battery has). NimH old style batteries composed of a number of SubC cells are 1.2V per cell, and Lithium Polymer (lipo) batteries are rated at 3.7v per cell. You may see an ESC say '10 cell/3s max' This means 10 nimh cells (10*1.2=12v), or 3 lipo cells ('S' always refers to lipo cells) (3x3.7=11.1). Or the same speed controller may say 12v max. Once you have identified that the ESC can handle your batteries, you need to look at the current rating (maximum AMPS) and make sure your motor draw will not exceed that. Most motors will say how many amps they draw 'under load' and 'burst'. As long as those amps do not exceed the 'continuous' and 'burst' amp ratings of the ESC, you are good to go. As a general rule of thumb, 25A ESCs are for micro scale stuff, 40A ESCs will do for most 1/10th stuff, 60A ESCs are for the heavy duty (very high kv) 1/10th stuff, 80A for light duty 1/8th stuff, 120A for midrange 1/8th scale stuff, and 150-200A for the really big 1/8th scale stuff.

    Batteries

    Nimh batteries (made up of smaller 1.2v cells) need to be maintained. After a month of being flat, they will rarely take a full charge again, at least not without careful resurrection using a complex cycling charger for many hours, apart from that, decent nimh cells should be fine for almost all your current needs.

    Lipo batteries are a little more trouble, but overall lower maintenance. The thing about Lipos is that they will generally start a fire if mistreated. Mistreated means; overcharged, overdischarged, badly damaged. These batteries must never be allowed to drop below 2.9v per cell. If this happens, first of all there is the fire risk if high current is still being pulled through it, but also a battery overdischarged in this way will never take a full charge again, and may visibly 'swell'. Therefore it's critical when using lipo batteries to use a speed control that has an automatic lipo cutoff, ideally one which you can set. When I have the option, I always set my lipo cutoff to 3.1v per cell. (so when a 2s (2 cell) 7.4v battery reaches 6.2v, the ESC stops the power to prevent battery damage). These batteries also need to be regularly balanced to make sure that the batteries stay at the same voltage per cell so that the lipo cutoff works properly. The danger of an unbalanced battery, is that eventually, if one cell in the battery were to fall to 2.6v, yet the other was still at 3.7v, that wouldn't be low enough (combined=6.3v) to activate the cutoff, but the first cell is already damaged beyond repair, having dropped below 2.9v. Balancing your batteries prevents these voltage mismatches. Most lipo chargers include a balancing charge option, which will do this automatically.

    The good thing about Lipos is that they charge fast (can be charged in an hour at the most, and many can be fully charged in half an hour), they do not lose much charge over time sitting around, they deliver incredible amounts of current, and last a very long time. Despite the extra care, these batteries are VASTLY superior to the other type, and I strongly recommend getting some and getting used to their idiosyncracies. Dont be put off by the extra care they require, follow these simple rules and they are very easy to own and will serve you well for many many charge cycles.

    Charge and discharge rating... When you buy a lipo battery, as well as the number of cells (2S, 3S, 4S, etc, which determine the voltage, 7.4, 11.1, and 14.8 respectively), and the duration expressed in mAh (milliamp hours), you will also see a discharge rating, expressed in 'C', for example, '2s 7.4v 5000mAh 25C'. This means it is a 2 cell 7.4v battery which will last for 5000miliamp hours and the maximum discharge rate is 25C. The C rating is an expression of how much continuous current (Amps) the battery can deliver safely (exceeding this can damage the battery and/or the ESC. The C rating is a formula based on the capacity. So, 25C on a 5000mAh battery is 25x5 (5000mA=5A), so this battery can deliver 125A of maximum continous current. A 40C battery of the same capacity would be able to deliver 200A of continuous current (40x5A=200A). Once again, it is important to match the battery to what your motor and ESC are capable of. To be honest, most batteries of 4000mAh or more at 20C or more are good enough for most applicatoins, it only starts to be a problem in the really high power 1/8th applications, where a 2650kv motor pulls say 150A continuous current. You would need to make sure that the C rating of your battery multiplied by its capacity makes at least 150 in order not to risk damage to the battery and/or ESC

    The same applies when charging. You may see a battery say it can be charged at 1C or 2C. Lets take the 5000mAh example again. 1C as we said=5A, 2C=10A etc. So a 'Charge at 2C' battery with 5000mAh capacoity can be charged at 10A maximum.

    Hope all that makes sense and helps.
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  3. #3
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    RE: rc electric noobie help needed badly

    electrics (especially brushless) require a fraction of the maintainance that nitros do.

    charge battery,
    plug it,
    drive,
    knock dirt off when done running,
    check for loose screws,
    put battery on charger,
    put truck on shelf till you are ready to drive again
    SC10rs, 1/6 hummer crawler, Kyosho Twin Force, Lunchbox project, Techone P51,

  4. #4

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    RE: rc electric noobie help needed badly

    Also what about the slipper clutch. what happens to proformance when you tighten loosen it.  are the pinion gears good to go for just backyard bashing. Thanks

  5. #5
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    RE: rc electric noobie help needed badly


    ORIGINAL: nitrosportsandrunner

    electrics (especially brushless) require a fraction of the maintainance that nitros do.

    charge battery,
    plug it,
    drive,
    knock dirt off when done running,
    check for loose screws,
    put battery on charger,
    put truck on shelf till you are ready to drive again
    The bold line above is important, both prior to driving and after. When giving my Rustler the first onceover out of the box, i found surprisingly many bolts and nuts being loose, and some of them in the steering linkage even too long. The car would have broken down after few minutes of driving. Tight them all up, but do remember to not overtight them.
    Good luck and have fun
    Find a job you love, then you won\'\'t have to work for the rest of your life.

  6. #6
    The_Shark's Avatar
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    RE: rc electric noobie help needed badly


    ORIGINAL: mjj002

    Also what about the slipper clutch. what happens to proformance when you tighten loosen it.* are the pinion gears good to go for just backyard bashing. Thanks
    a slipper is used to prevent gear damage when landing jumps (or applying power and brakes on high powered systems) follow your directions, too tight of a slipper will allow little or no slip, so while wheelies are more consistent (if you have enough power to do one), expect to replace some gears in the very near future, setting the slipper too loose will decrease acceleration and overheat very quickly, resulting in a damaged slipper and/or spur gear.

    you want it so if you hold the car on the ground and apply full throttle, you want it to bog down but you should see the slipper slip, you dont want the slipper to spin with almost no resistance (too loose) and you don't want it to lock up the whole system (nothing moves) this would be too tight.

    some manufactures tell you that you should hear the slipper slip for a few feet under full throttle from a stand still.
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  7. #7

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    RE: rc electric noobie help needed badly

    how can you tell when a battery is low. Will the esc just quite or do you run it out completly


    thanks for all the great help and info

  8. #8
    SyCo_VeNoM's Avatar
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    RE: rc electric noobie help needed badly

    ORIGINAL: mjj002

    how can you tell when a battery is low. Will the esc just quite or do you run it out completly


    thanks for all the great help and info
    NiMh it will stop moving, or come to a crawl

    Lipo you need a LVC(Low Voltage Cutoff) that will stop the RC (program it to 3.4V a cell IMO) they are in every brushless ESC I know of, or a LVA (Low Voltage Alarm) if you use brushed which are available for $4 on ebay and when your battery is at 3.4-3.3V's a cell it will make the most annoying buzz ever so you stop using the RC Lipo if you go under 3V's a cell you will damage the battery, and it could potentially rupture when charging.
    With great speed comes greater repair bills.
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