Electronics question

[Boomstick]

So I'm sitting here getting everything together to put my new Blackfoot together and looking over the radio instructions it shows hooking up a battery pack to the receiver. This is new. We didn't do that back when I started in rc unless you were running a mechanical speed controller. My traxxas doesn't have one either. Do I need a separate battery pack? It's a flysky fs-gr3.

[Fabia130vRS]

Why would you need it? Are you running a nitro car?

 

its just for binding or nitro models

[isomer1]

AFAIK you won't need the extra battery pack. As Fabia mentioned it's largely for nitro cars where you have no main battery, or for situations where you might run the main battery down too low and lose control. Running the receiver off the main battery will be called 'battery elimination circuit' (BEC) in most documentation.

[Boomstick]

1 hour ago, Fabia130vRS said:

Why would you need it? Are you running a nitro car?

 

its just for binding or nitro models

Ohhhh... Nitro cars don't use batteries so they need a separate pack... I didn't even think of that. I was thinking something else changed since I built my last truck nearly 30 years ago and now I need a separate battery for the receiver. 

With all the new (to me) technology out now, like brushless motors with 3 wires (I still don't understand how brushless motor even work, how DO you energize the com with no brushes???), lipo batteries with two plugs one of which you only use for charging, sensor/sensorless motors and esc's, radios with no crystals (again, something I don't understand the physics of) and no antennas to bend and break, slipper clutches, 550 motors (than make less rpm than the equivalent turn 540 but make cars twice as fast and never even get hot let alone burn off fingerprints), kv rating (kv is not kilovolts??? Darn), magical 8000 mah batteries that burst into flames while you are charging them instead of catching on fire when you're trying to pull 1800mah's out of an 8 cell nicad in 4 minutes because you geared the car to make as much speed as you can since the batteries only need to last 4 minutes. Now it keeps blowing the solder drop fuse so you wrap the little prongs with copper wire so it won't pop the fuse anymore (I burned 2 rc10t's and a jrxt to the ground back in the day doing that) 

All this stuff is new to me, it's like relearning the hobby all over again...  Like how am I supposed to time my motors if they don't have brushes??? What happened to pin tires in the rear and ribbed in the front??? Is tekin still around? Novak? Futaba? What happened to bolink? HOW THE HECK DID TRAXXAS TAKE OVER?!?!?!?!?!?!?!

Oh and I also forgot, there used to be only two ways to power an electric car, tamiya plugs (which caught on fire) or solder the battery right to the speed control (which caught on fire less often). Now there is twenty different plugs that come in twenty different sizes...

[simalarion]

I jump right to the plugs/connector, i changed all mine to XT-60 Amas, i think they are much better and easy to solder.

Yes those Tamiya plugs should be replaced

[Fabia130vRS]

Funny to read this

as for brushless... its just a magnet rotor pushed between the 3 static poles. 
 

as for motor kV ratingc easier then brushed motors.

 

you take your battery voltage lets say new 7.4V and multiply with motor kV... so 7.4 x 3300kV is 24.420 rpm/min

 

sensored motors communicate better with the esc as they have a sensor where the magnetic rotor is at the moment between the three static A B C poles.

Sensorless just knocks throttle to the motor neverming where it is between the poles

 

but there are tons of videos on youtube with great explanations as your are not alone with such questions

[rich_f]

29 minutes ago, Boomstick said:

I still don't understand how brushless motor even work, how DO you energize the com with no brushes???

Well I can help you on this one - a 'com', or commutator, is the part of a motor that transfers current from the stationary part to the moving via brushes. Since brushless motors have no brushes, they've no need for a commutator (no electricity goes to the rotor - only the outside, or stator, of the brushless motor is energised).

[Wooders28]

Brushed motors have their magnets around the inside of the can, and the windings on the armature.

In a brushless, it's switched over, the windings are around the outside, and the magnets are on the armature.

Instead of brushes, the esc is a mini computer, and works out the motor position, (either by a sensor on the back of the motor- sensored, or by powering up one coil, and seeing which other wire it gets a feed back from - sensorless) , and then works out which coil to energise next.

[mike in pa]

22 minutes ago, Wooders28 said:

Brushed motors have their magnets around the inside of the can, and the windings on the armature.

In a brushless, it's switched over, the windings are around the outside, and the magnets are on the armature.

Instead of brushes, the esc is a mini computer, and works out the motor position, (either by a sensor on the back of the motor- sensored, or by powering up one coil, and seeing which other wire it gets a feed back from - sensorless) , and then works out which coil to energise next.

Thanks for the easy description of the differences. 

[Mad Ax]

There's a lot to take in but if you break it down into small chunks it should be manageable

• Ohhhh... Nitro cars don't use batteries so they need a separate pack... I didn't even think of that. I was thinking something else changed since I built my last truck nearly 30 years ago and now I need a separate battery for the receiver. 

Early electric cars needed battery packs too.  Back in the early days, speed controllers didn't have built-in circuitry to send safe power to the radio (known as BEC or Battery Eliminator Circuit) - so even in early electric cars you needed to have a separate battery pack.  Almost all modern car ESCs have built in BEC and power is fed to the radio via the 3-pin servo plug, except on some Tamiya ESCs that still have a separate battery plug.

• I still don't understand how brushless motor even work, how DO you energize the com with no brushes?

As said above - there is no comm.  There are some good explanations already above, but I think of it like this: the motor shaft is basically a powerful magnet, and the coils are embedded in the can.  The ESC pulses power to the coils to make the magnet rotate.  Lack of brushes means less physical parts to wear out and less drag, also a single magnet is easier to balance during assembly than a wind of heavy wire.  The technology to rapidly pulse high current to different coils has only recently been affordable on the hobby market.  There are many benefits to brushless (more power per volt, longer run times, less maintenance) but some drawbacks (more sensitive to heat, overheating will damage the magnet and reduce its power permanently, more prone to back-EMF if using long battery leads which can damage the ESC - don't use long better plug convertors on brushless ESCs.  Motor leads can be as long as you need, within reason).

• lipo batteries with two plugs one of which you only use for charging

Your old NiCad packs from the 80s would have benefitted from this too, although the technology was prohibitively expensive then and 6+ cells per pack would have made the balance leads annoyingly chunky.  But if you could reliably charge each cell individually to capacity, you would have less chance of one cell dumping prematurely in a race.  Particularly with NiMH packs, when one cell dumps, its internal resistance increases, and when connected in series with the rest of your NiMH cells this saps the power, so one dumped cell equals a sudden drop in total power to the motor.  The problem compounds when recharging in series, because those cells that didn't have time to dump will reach full charge first and signal the charger to shut off before the dumped cell has got back to full charge again.  Over time it just gets worse.  That's why racers used side-by-side packs and discharge boards to make sure all cells were completely flat before recharging.

The balance lead is a bit more critical with a LiPo pack since LiPo cells don't give a 'peak' when they reach capacity, they just keep accepting charge until they catch fire.  So if one cell was as significantly higher charge than the other and you charge both in series, the higher charged cell will reach capacity and catch fire while the total battery voltage is still lower than full capacity, so the charger has no idea what's happening.  The balance lead reports the charge state of each individual cell to the charger so it can shut off before any cell is at risk of catching fire.  IIRC they can also charge individual cells at low current via the balance lead once the main charge is complete.

• sensor/sensorless motors and esc's

In order for a brushless ESC to effectively control the motor, it needs to know where the magnet is in relation to the coils.  Some use a sensor (sensored) - a sensored motor has an additional plug on the back (iirc 6 pins, but I don't have one next to me to check) which needs to be connected to the ESC.  Sensorless systems detect feedback in the coils to know approximately where the coil is.  Sensorless combos aren't as smooth (especially at low RPMs) and can 'cog' if they struggle to detect the comm position, causing the motor to chatter and the car to not move.

Not all motors have sensors and not all ESC can operate without sensors, so it helps to know when you're buying. 

• radios with no crystals (again, something I don't understand the physics of) and no antennas to bend and break

You don't need to understand how it works, just accept it and enjoy it.  FWIW it works in a similar to your home WiFi (which also uses 2.4GHz).  There is an antenna, it's just much smaller because the frequency is higher.  Antenna length is related to radio frequency, hence why long wave radio enthusiasts have huge steel structures on their sheds.  Early 2.4GHz transmitters had stubby antenna on the back with a hinge on the base, exactly like the ones on your old 2.4GHz router.

• slipper clutches

These have been around for a while at competition level but the rise of high-power brushless systems and much gripper track surfaces and tyres means they're more important and making their way into non-competition cars (especially anything heavy or with a high power system)

• 550 motors (than make less rpm than the equivalent turn 540 but make cars twice as fast

A big block Chevy makes more grunt than a Honda VTEC but doesn't spin as fast

• and never even get hot let alone burn off fingerprints

That's all down to timing, power and load - the big block analogy falls down here because an internal combustion engine makes heat even if it isn't doing work and tuned American V8s are prone to overheating when pootling along in town centre traffic - but with enough voltage and enough load you could take your fingerprints off with a 600 can

• kv rating (kv is not kilovolts??? Darn)

No, I thought that, too, to start with.  Kilovolts is kV, this is Kv.  It means - the number of turns the motor will make when 1 volt is applied, with no load.  The higher the number, the more the motor will spin.  A higher Kv motor will turn faster with no load.  However it isn't the full story - a 600 can rated at 2200Kv connected to a 4S LiPo will spin at the same speed as a 540 can rated at 4400Kv connected to a 2S LiPo, but the 600 will make much more torque.

• magical 8000 mah batteries that burst into flames while you are charging them

These revolutionised power as much as 2.4GHz radios revolutionised control.  They have been demonized by some, and mistreated they will burn your house down, but read up on proper battery care, look after them and follow the guidelines and you'll be safe.  As you well know, you can start a fire with a NiMH - you can also explode a cell under charging and destroy your chassis.

• instead of catching on fire when you're trying to pull 1800mah's out of an 8 cell nicad in 4 minutes because you geared the car to make as much speed as you can

Keep your gearing appropriate and keep the current draw within the confines of the battery - you can make a LiPo catch fire under load if your gearing is wrong (I puffed two packs in succession during a race meet in 2019 because my gearing was wrong and the packs couldn't cope with demand).

• the batteries only need to last 4 minutes

How does 20 sound?  I run two 5-minute heats on a single 4000mAh LiPo in vintage racing.  I only need three batteries for a whole day.  My crawlers will run for over an hour on single battery.

• how am I supposed to time my motors if they don't have brushes?

Same as you would time them if they did have brushes.  The sensor can be fooled by twisting it on the back of the can.  It assumes it's being triggered at 0 degrees but you've turned it to the 5 degree position, so the ESC switches early.  You'll have less power and more heat low down, but you can get more speed at the top.  Also because ESCs are computer-driven, you can program advance into them, and you can even run an 'advance curve' so they are low advance at low RPM and high advance at high RPM - just like you can with a modern EFI system.  Exactly what you can do varies with how much you spend on your ESC.

• What happened to pin tires in the rear and ribbed in the front?

Modern surfaces happened.  Out is clay and grass and largely carpet, in is astroturf with sand substrate.  Grip is much higher.  Now it's not about getting as much grip as possible from your tyres, it's about tuning the grip out.  There's a huge range of tyre compounds and tread styles for wet, dry, hot, cold, and everything in between.

• Is tekin still around?

Yes

• Novak?

No

• Futaba?

Yes

• What happened to bolink?

Long-gone, I think, but last year I had the pleasure of watching several Diggers competing hard at a vintage race meet.

• HOW THE HECK DID TRAXXAS TAKE OVER?

By selling cars with chromed wheels and funky pre-painted tribal paint themes that actually went fast and didn't break, providing good customer service and marketing them to people with disposable income and short attention spans.  Then by using their substantial market presence and a complete lack of morals to legislate their competitors out of business.

• there used to be only two ways to power an electric car, tamiya plugs (which caught on fire) or solder the battery right to the speed control (which caught on fire less often). Now there is twenty different plugs that come in twenty different sizes...

True, and the world is a richer and safer place for it Tamiya plugs are still rubbish, for a long time Deans were considered the best, but various rivals have stepped up.  I still find Deans easiest to solder, but more fiddly to unplug (especially after a cold race with icy wet fingers).  XT60 are popular in 2-3S applications, XT90 in big power installs.  I can't get the hang of XT60 soldering, I keep melting the plug out of the plastic before the solder runs.

I hope that helps - enjoy your return to the hobby