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  1. #1
    Anomie's Avatar
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    RC Resources for the beginner [Read this first]

    This resource thread was created to group together some helpful guides and assist both those new to RC and those who are experienced but need some reference. The links here can be added to if and when newer guides become necessary or requested. If you would like to see something included here which would benefit newer members, you may contact me or any car moderator and your request will be added.

    Beginners to RC - This thread is helpful for answering many of the questions which arise when trying to decide on what type of RC vehicle to purchase: Before you ask what RC you should buy READ THIS

    Understanding electric power - brushless and lipo explained by Foxy - See post below or click here...

    Everything you need to know about LiPo batteries - A detailed guide to using lipo batteries by Foxy - click here...

    Tuning your suspension - Good information for anyone lookin to maximize the suspension on their RC: Car Tuning

    Understanding gearing - Internal Gear Ratios Explained
    Last edited by Foxy; 09-15-2013 at 02:50 AM.
    ~Reiko~

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  2. #2
    Community Moderators Foxy's Avatar
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    RE: RC Resources for the beginner [Read this first]

    Electric 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 couple months 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, though cannot reach the performance of lipo.

    Lipo batteries are a little more trouble, but overall lower maintenance. The thing about Lipos is that they could start a fire if mistreated. Mistreated means; overcharged, overdischarged, badly damaged. These batteries must never be allowed to drop below 2.7v per cell (2.7 is an arbitrary recommendation, the point of no return is more like 2.4 volts, however, I'm going to say 2.7 for safety). 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 3.0v per cell. (so when a 2s (2 cell) 7.4v battery reaches 6.0v, 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 2.5v, yet the other was still at 3.6v, that wouldn't be low enough (combined=6.1v) to activate the cutoff, but the first cell is already damaged beyond repair, having dropped too low. 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 calculated based on the capacity. So, 25C on a 5000mAh battery is 25x5 (remember 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 regularly. 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 capacity can be charged at 10A maximum.
    Last edited by Foxy; 12-11-2013 at 10:24 AM.
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