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  1. #1

    been out of the game and dont understand how brushless and lipo work.

    I have been out of the game for a few years, i used to run when everyone used brushed motors and crystal transmitters and recievers. I am currently making my tc3 up to modern specs. I also just bought a new rolling chassis.i understand that if you buy a brushless motor, it needs a matching esc and lipo battery. Can someone please enlighten me on how these work together. I am currently stuck because i do not know that to pair with a motor or how you know what works together?
    thanks!

  2. #2
    Maj_Overdrive's Avatar
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    Everything you need to know about LiPo batteries...

    That'll get you started and explain the Lipo side pretty well. Brushless isn't all that different from brushed. There's still a motor and esc but the "turns" in a motor don't mean as much as they used to. Instead we use "kv" now, which is just a way of expressing how fast a motor will spin (unloaded) per volt that is applied. Example a 4000kv motor will spin 4000rpm when one volt is applied to it. There's more sizes of motor availible now too but there's still the familiar 540 and 550 can sizes especially in racing classes. Brushless is also more demanding on the batteries so going Lipo is almost a must. In some cases NiMh can actually hurt the esc due to ripple voltage.

    Another big big difference is Sensored vs sensorless. Sensored motors have a sensor on them to tell the esc the position of the motor. Sensorless motors don't have a sensor and instead use EMF signals coming back through the motor wires to determine the motors position. Sensored has smoother startup and low speed drivability so it's the choice of crawlers and can be an advantage while racing. Most sanctioned race tracks require sensored in their professional and sanctioned races. It's possible to run sensored motors on sensorless esc's but the motor may not like it too much. Some esc's can run either sensored or sensorless while others cannot.
    Punch Control? I don't need no stinking Punch Control!

  3. #3
    SyCo_VeNoM's Avatar
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    Generally though ESC's should meet at minimum what the motor can pull. Like a 60A motor you do not pair up with a 35A ESC as it will smoke the ESC. On the flip side you can put a 35A motor to a 60A ESC as the ESC will only give the motor what it asks for.
    There are also other considerations is the motor sensored as then it needs to be paired upto a sensored ESC, and wired correctly (a-A, B-B C-C), whereas a sensorless motor the way the wires are plugged in don't matter.
    So this leads me to ask what motor in particular did you get?
    Side note unlike brushed NEVER connect the brushless motor to a battery directly as the motor functions on a 3phase setup, and if you plug ay 2 to the battery it will damage the battery.



    As for lipos you more match the battery compartment size(as lipos come in a variety of sizes), then select a S-rating, and C-rating based on the motor and ESC setup

    Basically C-rating is to figure out how much current the pack can safely put out (C-Rating X mAh rating)/1000 = total amps
    like for example lets say I have a pack rated 5200mAh 35C if you plug it into the formula (35X5200)/1000= 182Amps total the pack can put out. So basically the pack is safe for any 1/10th vehicle, and most 1/8ths (BTW those are real numbers pulled off a pack of mine)

    Now the #S rating that is a multiplier for voltage the formula is #S X 3.7 = total pack voltage. Example 2S lipo is 2X3.7 which makes it 7.4volts.
    S is actually a reference to how many cells are in the pack as each cell is 3.7volts
    For the record this is nominal voltage a fully charged lipo is actually 4.2volts per cell.



    RC Resources for the beginner [Read this first] this post goes more in depth on what I said



    Maj nice find couldn't find that post I knew it was a sticky, but no longer see it probably got lost when the forums swapped software
    With great speed comes greater repair bills.
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  4. #4
    Maj_Overdrive's Avatar
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    I don't think it ever made it to sticky status but it definitely should be. I just looked for a post by Foxy and luckily it's near the top of his "recently started threads" so it was easy to find. I kinda zoned out after reading the first half of the OP's post though and missed the rest. Thanks for picking up the slack! Lol
    Punch Control? I don't need no stinking Punch Control!

  5. #5
    nitrosportsandrunner's Avatar
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    you don't "have" to use a lipo battery with a brushless system. A nimh battery will work. But a brushless system will want more amps than a brushed, so the demand on the battery is higher. But if you currently own some good quality nimh packs, you can use them.
    That said, running a brushless system on a nimh battery is like running a race engine on pump gas....high octane fuel will give you the max performance just as a lipo will give the most from the brushless system.

    A brushless motors construction is opposite of a brushed. The coils are on the inside of the can.....the magnets are on the rotor. Thus, there are no metal brushes needed to transfer the power to the coils. this means no lose of power, no friction and less heat. Thus, they are more efficient.

    A lipo battery is fully different in construction from a nimh pack. each cell has a fully charged voltage of 4.2v. Thus, a 2s (2 cell) lipo is nearly 8.4v when fully charged. The same power is achived with a lighter battery pack. The cells are chemicals in a semi-soft case (not a several heavy metal cases)

    A lipo cannot be discharged below 2.8v (technically 3v....but I have had some get as low as 2.8v and still be able to recharge them) cell phones use similar batteries, and that is why they turn themselves off with the battery is low, so they don't over discharge.

    A lipo typically has a better discharge rate....meaning the amount of amps it can put out is better. And they voltage they deliver stays near nominal (7v for a 2s pack) right up until the pack dumps and it is time to recharge them. this is unlike nimh packs which slowly dump (drop voltage)

    Most brushless (and today some brushed) speed controls can read the voltage of the lipo and cut power to the motor when it is time for the battery to be charged, thus you don't risk over discharging them.

    short story: 6 years ago I would spend $50 for a good brushed motor, $50 for a good nimh only to get 30mph and 12 minutes of runtime.
    Today I can spend $50 for a brushless motor and $30 for a 2s lipo and get nearly 40mph and drive for 25+ minutes!
    SC10rs, 1/6 hummer crawler, Kyosho Twin Force, Lunchbox project, Techone P51,

  6. #6
    EXT2Rob's Avatar
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    I disagree with you, Nitro, on the NiMhs. Yes, IF you had REALLY GOOD NiMhs, and you just happened to have an ESC that was engineered against ripple, and that ESC (and motor) were only rated at 35Amps, or less, then you might get away with the NiMhs. (Not on a Castle system tho!)

    But I'd never run them. Lipo only. NiMhs are for brushed systems. and even then.......Lipo is so much better.

    As for what system to get, you should look for a system, or combo....that is, a motor and ESC that's already paired as a package. Lots to choose from.
    If you're not planning on racing or crawling, a sensorLESS system will do ya just fine, and is generally a little cheaper than a sensored system. I would suggest looking at the HobbyWing EZrun or Xerun combos at HobbyPartz.com Great systems for budget prices, and the combos frequently come with a programming card for setting the options in the ESC. Other companies charge you extra for that. Castle Creations make popular systems, and their motors are excellent. But IMO, their ESCs in the past have not been the most robust. They have come out with new versions tho lately, so maybe they're better now. (My buddy and I fried both our Sidewinder Sv2 systems, I think because we were using NiMhs at the time)

    "What motor KV should I get, then?" will be your next question. That will depend on your car and how and where you drive. I'm not familiar with the TC3, so maybe someone who knows the car can advise you better, but I'd guess that something around 4000KV would work well for you. 4000kv on a 2S (two-cell) Lipo will be pretty fast. 5600kv CRAZY fast.

    I highly recommend this charger: Thunder AC680 Professional Dual-Power LiPo Balance Charger Discharger w AC Adapter for 1-6 Lipo 1-15 Nimh + USB to PC Software Less than $60 and does everything you need, quietly.

    I also suggest looking at the FlySky GT3C radio for $39. 2.4ghz is where we're at today, and FLySky makes good sportsman (basher) grade stuff. The GT3C can be bound to ten different RCs. If you really want to go cheap, the single-car GT2 is only $20.
    Just a schmoe....

  7. #7
    nitrosportsandrunner's Avatar
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    I have never heard the term "ripple" ext2rob...what is that?
    if nimh on a brushless is so bad, why does traxxas sell most with a 7cell nimh?

    I certainly agree that lipo is better...whether for brushless or brushed. hands down they are better batteries. and even a 7cell nimh wont get as much out of a brushless system as a 2s lipo. IMO it is fine to run nimh on brushless....but I feel the biggest drawback is that the nimh packs will wear out much faster due to the higher amp demands on them. I have a fairly new 4200mah nimh that got up to 140 degrees after running it in my brushless kyosho twin force. much warmer than if it had been used in a brushed model.

    I would not suggest to anyone to BUY nimhs for a brushless system. but if you already have nimhs I say use them (unless you know someone just getting into the hobby that has brushed stuff they could use them in) But since a 2s lipo costs less than a quality 6cell nimh in many cases, it makes sense if you are buying batteries for you model to go lipo.

    Ive been using the thunder AC6 for a year now, no issues. it is awesome that we can get 2s lipo and a good charger for under $100. I used to pay $50 for a good nimh pack years ago....a pack which isn't half as good as a $30 2s lipo.
    SC10rs, 1/6 hummer crawler, Kyosho Twin Force, Lunchbox project, Techone P51,

  8. #8
    EXT2Rob's Avatar
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    I hear ya, Nitro. True, if ya got 'em, ya might wanna just use 'em up. BUT, I would feel better being forewarned that doing so might damage not only the battery pack, but the ESC as well.

    I don't have a real good technical explanation of ripple current, I should look it up. But my understanding is that it occurs when an electrical system (motor & ESC) tries to draw more current than the supply (the battery) can manage. This causes the voltage and amperage to get out of phase, which can cause back-voltages that can exceed the voltage ratings of certain components, causing their failure.

    Can I PROVE that ripple is what killed my Castle Sidewinder? No. But it's the only explanation that makes any sense to me, considering that the ESC died about three months after using NiMh packs. And, those NiMh packs were pretty much destroyed too, by the system pulling so much current, that the shrink wrap on the packs melted, and they'd no longer hold a charge. (ANother reason NOT to use NiMhs on brushless) As in all things electronic, heat is bad.

    Why does Traxxas supply NiMhs with their RTRs? Cuz they're cheap! (You can take that any way you want) And if something gets damaged, they make more money cuz you have to buy a replacement. Money money!
    Just a schmoe....

  9. #9
    EXT2Rob's Avatar
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    Google-ing "What is "Ripple Current"?" yielded a number of hits explaining ripple current as the inflow and outflow of current from a filter capacitor in an AC/DC rectifier circuit. Most of them talked about ripple current in terms of a cap's ripple current rating, i.e. how much ripple can a given capacitor filter without burning up. So how that applies to our DC-powered motor systems, I'm not sure. Someone with more intimate knowlege of how these things do what they do would have to come along here.... I used to work in electronics, but not with motor systems and the related control circuits.

    The explanation of ripple currents as it relates to RC that I gave above comes from my reccollection of one that I read somewhere, maybe here.
    Just a schmoe....

  10. #10
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    Ok. My thought.

    there is nothing wrong with using a nimh or nicd pack on a brushless system providing the system is not drawing more current that the battery can supply.... But the catch is..... Generally speaking most rc cars on a brushless combo will exceed the current draw of a nimh or nicd. There are acceptions for example, 1/10 touring cars, 1/10 crawlers, 1/8 crawlers and other smaller vehicles(1/12 and under)

    exceeding the the batteries current limit can cause a few issues
    ripple
    Very excessive voltage drop
    very extreme heat
    internail battery failure

    each one of those can cause issues, voltage ripples have been knowen to fry ESC
    excessive voltage drop with cause the receiver to reboot
    minh battery's have and will get hot enough to start melting it self and the chassis, and I have heard they can catch fire if they get hot enough.
    LOSI: 5IVE-T, 8IGHT-E, MICRO SCT
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