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Thread: Speed Controllers - Making Sense Of It All

  1. #1
    RogueTwoRobots's Avatar
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    I’ve noticed a few new builder threads lately where, in the component list, a brushless speed controller is chosen to control a brushed motor. While those of us who have been competing for a while know that won’t work, it’s not always obvious when someone is starting out and it can be a bit of a daunting area, so I thought I’d write a quick post to help out and link to some suitable and commonly used parts.

    The Basics

    I’m not going to into too much technical detail here, just keeping it simple. The key difference between brushed and brushless motors is the number of connections it has. Brushed motors usually have two connections, tabs or wires on it; brushless motors have three. This is because the copper windings in brushless motors are arranged in phases. If you take a battery and touch the positive and negative to the two connections on a brushed motor, the motor will turn. If you try to do the same to a brushless motor, it won’t work.

    Brushed: http://za.rs-online.com/largeimages/F2483716-01.jpg
    Brushless:https://ae01.alicdn.com/kf/HTB12aJfL...tor-b-font.jpg

    For the moment, and when starting out, brushed motors are easier to use for drive motors. Brushless motors are becoming more and more suitable for use as drive motors in featherweights, but it can take a bit of experimenting with the computer code used on the speed controller and often the motor itself needs a bit of modifying. When starting out, all of that can seem very intimidating, as you don’t want to risk damaging expensive components if something goes wrong, hence why easy to source parts such as cordless drills are great for providing an almost-ready-to-roll drive system.

    Speed Controllers


    Because brushed and brushless motors are different, they require different types of controllers. Again, the main way to tell them apart is in the number of connections, or wires.

    Most speed controllers have wires coming out either side of a circuit board, often protected by some sort of casing (though occasionally all wires can come out the same side). On one side, there’ll usually be a red and black wire – to connect to the positive and negative of the battery/power supply – and a thinner 3-strand wire with a small connector on the end; this connects to the radio control receiver to send the speed controller the signals received from the transmitter.

    On the other side of the circuit board/casing, you’ll either have two wires coming out, or three wires.
    If it’s two wires – it’s a brushed motor speed controller: http://www.mtroniks.net/images/XL/Marine20HV.jpg
    If it’s three wires – it’s a brushless motor speed controller: http://drone-about.fr/wp-content/upl...10/ESC-25A.jpg

    That’s literally the main difference between each. Two wires, it goes to the two connections on a brushed motor; three wires, it goes to the three connections on a brushless motor.

    Due to brushless motors becoming the standard motor used in RC hobbies, it’s becoming more and more difficult to find suitable speed controllers for brushed motors, so here is a list of some suitable controllers. The key figure in almost all speed controllers is the Amp (A) rating. For motors such as cordless drills, you want to be looking for controllers around the 10-15A continuous mark as a minimum, and the higher the better.

    Dimension Engineering
    Sabretooth 12A: http://www.technobotsonline.com/sabe...er-for-rc.html
    Sabretooth 25A: http://www.technobotsonline.com/sabe...er-for-rc.html

    The Sabretooth controllers can be a bit hit and miss sometimes. Some people have run them without issue, others have had them fail despite not exceeding their limits. They can seem a bit pricy but it’s worth noting that these are dual motor controllers, so they can control two motors, meaning you only need one for a two-wheel-drive robot.

    Robot Power
    Scorpion XL (12.5A): http://www.robotpower.com/products/s...n_XL_info.html
    Scorpion XXL (20-25A): http://www.robotpower.com/products/s..._XXL_info.html
    http://www.robotshop.com/uk/scorpion...or-driver.html

    Again these are dual controllers, and again they are a bit pricy. They do seem to have a better track record compared to the Sabretooths (I have used a couple of XLs without issue) and they have built-in current limiting, meaning you’re less likely to blow them up by drawing too much current. They’re also America-based so you usually have to factor in shipping and customs, however the XXL is available from a UK supplier, see the second link for it.

    At this point it’s worth me saying that the Scorpion XL/XXL and the Sabretooth controllers don’t have wires coming in or out of them. Instead they have screw terminal blocks that you can connect your wires into.

    Botbitz/Ranglebox
    30A ESC: http://botbitz.com/product/botbitz-3...ed-controller/
    http://ranglebox.com/product/botbitz-30a-brushed-esc/

    85A ESC: http://botbitz.com/product/botbitz-8...ed-control-v2/
    http://ranglebox.com/product/botbitz...2-brushed-esc/

    Both of these are single channel controllers, meaning they can only control one side of drive. You would need two for a 2WD robot.
    To confuse things a bit, these are actually sold originally as brushless controllers, but the guys at Botbitz wrote new code for them to convert them to brushed controllers! Botbitz is based in Australia so you need to factor that in when buying them. Ranglebox is a UK distributor of the Botbitz products, making them available closer to home.

    eBay/Miscellaneous
    320A ESC: http://www.ebay.co.uk/itm/320A-7-2V-...AAAOSw~OVWwaAK

    There are various types of brushed speed controller on eBay with no particular branding. The 320A rating of this model isn’t really accurate, but would be more than suitable for featherweight motors. However, while they are cheap, they aren’t always as streamlined or as precise as the more expensive options. Key issues tend to be that reversing capabilities aren’t great, the deadband (the amount you have to move your stick on the transmitter before the speed controller starts turning the motor) can affect operating performance and there is no braking, so when you take your finger off the stick, the motor coasts to a stop rather than stopping immediately. All of these issues tend to make the robot very difficult to control. Our best advice with these speed controllers is don’t buy them. Save your money and get one of the more expensive controllers that will do a better job and be more useful in the long run.

    FeatherTwo
    Rory Mangles, of Team Nuts, also makes featherweight brushed speed controllers for a very reasonable price: https://docs.google.com/document/d/1...X9DFu5AJk/edit

    These are dual ESCs so, again, only one is needed. You might be thinking ‘why are there four wires coming out one side of the circuit board?’ These are just the wires that go to the motors. The two reds go to one motor, and the two blacks to the other.

    Don’t Be Fooled!
    Beware of some brushed speed controllers such as this one: https://hobbyking.com/en_us/turnigy-...ushed-esc.html

    They look suitable and are incredibly cheap, but they’re designed for use in planes and some RC cars where reverse isn’t required, so they only run in one direction. Not ideal for a combat robot!

    Hopefully that gives those of you starting out some useful information. If you’re ever unsure of your component selection though, always post your thoughts here before buying, and we can advise you if they’ll work or if you need to be looking at different parts.

    Happy roboteering!
    Jamie McHarg
    RogueTwo Robots
    http://www.rogue-two-robots.vze.com

    With great power, comes great reliability.

  2. #2
    R9000's Avatar
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    Geez I'm so glad you made this. I was thinking about making some kind of a thread for this, but this is excellent information. This thread needs pinning or something.

  3. #3
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    Great thread, wish it would have been there a few months earlier so i could have used it^^

    Maybe worth mentioning are these ESCs: http://www.robots.ib-fink.de/index.htm
    Everything on the homepage is in german, but these are made specifically for fighting robots, and since each is made by hand, you could get customized ones or combinations of features... Plus a very detailed program available via USB to change a lot of parameters and including channel mixing if you want to drive with one stick (so they are dual), some version also including the possibility to attach two drive motors and one (brushed) weapon motor and/or valves for pneumatic stuff to it.
    As far as i'm aware almost every roboteer in germany uses at least one of these in at least one of his bots.

    Also, they have a fuse instead of current limiters. They had in earlier versions, but those tended to make the bots "stutter" in situations where stall currents occurred. So now... before you melt your ESC, you melt the fuse (but that would take some time), and can replace it cheap.
    Last edited by Runsler; 6th February 2017 at 05:46.

  4. #4
    maddox10's Avatar
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    Never had a fuse go on an IBF, and we use'm in all or feathers now.
    And that's using the GR02's or Neptunes sleightly overvolted (4S on the 12V versions)

  5. #5
    RogueTwoRobots's Avatar
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    Good point Jan, something I forgot to put in the original post. Anyone who has any other speed controller recommendations, please feel free to add them to the thread
    Jamie McHarg
    RogueTwo Robots
    http://www.rogue-two-robots.vze.com

    With great power, comes great reliability.

  6. #6
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    The Ragebridge 2 is a well regarded two channel brushed ESC in a reasonably small package http://e0designs.com/products/ragebridge2/

    The Robot Power Vyper is a single channel ESC with a high 120A current capacity. Its a bit overkill for most featherweights but would work well in a pushy bot that has lots of traction http://www.robotpower.com/products/vyper_info.html

    The IFI Victor 885 is another high power 120A single channel ESC. Its a bit old school but still very dependable and most compact than the Vyper. http://www.robotmarketplace.com/products/0-238.html

  7. #7
    RogueTwoRobots's Avatar
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    Worth mentioning that the speed controllers Nick lists above, particularly the Vyper and Victor models, are also suitable for running a variety of commonly used heavyweight drive motors, so they could be seen as a longer term investment if you have one eye on building a heavyweight in the future.
    Jamie McHarg
    RogueTwo Robots
    http://www.rogue-two-robots.vze.com

    With great power, comes great reliability.

  8. #8
    overkill's Avatar
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    The reason I like higher powered ESCS is that I don't want them to be the weakest link in the drive train. With Lipo batteries now able to deliver stupid amounts of current, I'd rather fry a cheap motor than the ESC.

  9. #9
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    I think if this becomes a "sticky" then it's worth mentioning that I found the dual motor controllers are a lot simpler over the "esc per motor" setup when starting out. I say this from the point of view of someone that had no one to physically ask when first starting out. I think if you get into it through friends etc. it's different. Things such as cutting one of the BEC's, not realising my cheap transmitter wouldn't do mixing, then when I bought another it wouldn't get full throttle etc. When both motors and the mixing are done by the ESC it just becomes a case of faffing for 10 mins to get it calibrated and running right with the handset trims and swapping + and - about a bit. The other big thing was that I built my first feather without soldering as most of the dual controllers have terminal blocks built in.

  10. #10
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    http://www.fightingrobots.co.uk/thre...ight=dx6i+hack

    Might be worth linking this thread for TZ's. A healthy price cut for the slightly more adventurous.

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