Brushless 101 - good read

[Lonestar]

All

came upon this article here:

http://www.actionrc.com.au/?p=2595

I've seen (and even written) my share of internet content on BL basics, but this is one of the, if not THE best onboarding I've stumbled upon so far as it answers most of everyone's basic questions (sensor/less, timing variations, winds nomenclature, ...)

Intro to brushless motors…

If you happen to be new to brushless motor tech, you might be interested in these notes I put together for the Tassie crew. We have a few guys here adding 10th SC trucks to their nitro buggy/truggy habit, and wanting to know about 10th scale brushless motor tech.

Read on if you’re interested, and feel free to ask questions, make comments, or correct mistakes!


History

Brushless motors have only been used in R/C cars in the last few years. Prior to the introduction of brushless motor technology, old-school “brushed” motors were used. Standard brushed motors feature a can with fix magnets, housing an “armature” wound with wire. The motors work by passing electrical current through a set of carbon/copper “brushes” mechanically connected to a copper “commutator” at the top of the armature/wire stack. There is a heap of friction, heat and wear. High powered brushed motors are inefficient, need a lot of maintenance and can be very unreliable.

Brushless tech turns the motor inside out. The rotor is a permanent magnet, and the can holds the wiring for the electro-magnet. There is no mechanical drag apart from the ball bearings, nothing to wear out. Efficiency is improved, performance is improved, reliability is improved.

The first brushless motors used in car racing were adapted from planes/helis. There are very different power demands in these different applications. Plane motors can be much more powerful than car motors, but tend to run at fixed throttle openings, and relatively high motor speeds. Cars uniquely need motors that can be very smooth from zero to maximum revs. Motor designers struggled to make brushless motors do this, and it took a few years before they progressed far enough that for the race market, bl motors were superior.

Novak released their first serious race motors and esc in 2005 (the Velociti/GTB combo) – and within two years, the vast majority of open (modified) class racers were using bl motors. Spec classes (stock, superstock) took a while longer while manufacturers and rule-makers settled on a formula for BL motors. Spec BL motor classes have only become commonplace in the last 18 months or so.

Sensored or Sensorless

There are lots of variations in BL motor tech, but one of the main ones is the difference between sensored or sensorless motors.

In a simplified nutshell, the difference is this. Sensored motors use “Hall Effect Sensors” installed in the endbell of the motor to monitor the exact position of the rotor at all times. This information is fed back to the ESC and enables very precise control of the motor. Sensored esc/motor packages are generally smoother in power delivery than sensorless motors, particularly at low or zero revs where sensored motor/esc packages (particularly the cheaper ones) struggle to deliver power smoothly and can “cog” or stutter.

Sensorless motors don’t have the mechanism to know exactly the position of the rotor – and as a result can’t always deliver power smoothly at zero or low revs. This is particular evident if you crash (sudden stop) or are rolling backwards and apply forward throttle. Sensorless motors can struggle in these cases. On the flip side, sensorless motors can deliver massive horsepower, and the better (read “more expensive”) esc’s are managing the position/cogging issue much better these days.

10th scale race organisations all over the world (from world IFMAR, to US ROAR, and Australian AARCMCC) insist on sensored motors for 10th scale racing. The motor design and size is tightly controlled, sensor design specified, and cabling specified so that all race-oriented sensored escs and motors can be plugged into each other.

In 8th scale most of the ESC’s have so far come from the “hobby” side of the industry, and are sensorless. Race manufacturers like Novak, Tekin, LRP and Speedpassion are in their first generation of releasing sensored motors. The jury is still out as to whether 8th EP offroad will end up moving toward sensored or sensorless.

Winds or KV?

BL Motor manufacturers tend to market their motors in one of two ways.

Hobby-oriented companies use a standard KV rating. This is the number of revs the motor can be expected to deliver per Volt applied. Typical “bashing” motors range from 3000-5000KV. With a 7.4v 2s lipo, that means a 3000kv motor will deliver 22200 revs at full throttle….if all other things are equal. Theoretically all motors of the same KV rating should deliver the same performance – except that KV doesn’t take into account torque, or timing – both factors that impact on performance hugely. The higher the KV number, the higher the performance

Race-oriented manufacturers on the other hand market their motors based on “turns” – the number of turns of wire wrapped around the wire stack. A 17.5 turn BL motor will have 17 1/2 turns of wire wrapped on it’s stack, while a 5.5 turn motor will have 5 1/2 turns. In simple turns, the less wire (lower turns), the more power. Race manufacturers will sometimes supply KV ratings as well, but in racing terms, outright KV is not always the most important factor. Rule makers (like ROAR for US and AARCMCC for Australia) have been very specific in developing rules particular for spec motor classes – so manufacturers have no choice but to build motors to those specifications (in terms of number of turns of wire of specific guage) if they want to receive approval and sell to the racing market. Open (modified) class EP racers use motors that can range from 4.0 or 4.5 turns (for touring car racers) down to about 8.5 or 10.5 turns (for offroad where outright power is not useful). A 4.0 turn bl motor can be up to 10000kv – or 74000rpm with a 2s lipo. That’s why EP touring cars will do nearly 100km/h!

Spec BL Motor Classes

I mentioned above that rule makers have been very specific about spec motor classes for BL motors. Worldwide there are three main spec motor classes. These are 17.5 turn, 13.5 turn and 10.5 turn.

IN Australia, both on-road and off-road racing features 17.5 turn (called “Stock”) and 10.5 turn (called “Super stock) class racing. In the US, 13.5 is the spec motor used in their Super stock class of racing.

It is difficult to compare precisely, but a 17.5 turn spec brushless motor is roughly equivalent to a proper 27t brushed competition motor. A 10.5 spec BL motor roughly similar to a 19 turn brushed motor. Note these are comparing competition oriented motors. The motors supplied in standard SC trucks (eg the 17t in the SC10) are not competition grade, so the comparison gets a little messy.

For SC racing in Tassie (and in many other Australian clubs) we are recommending the 13.5 turn spec brushless motors. Performance is roughly equivalent to the standard motors, but power delivery is still smooth enough to make SC trucks manageable. More horsepower (eg the 10.5) just makes them too difficult to drive.

Spec motors are also relatively easy to scrutineer to ensure that everybody is using the right/same motors. All spec BL motors are sensored and will need a sensored ESC to drive them.

which brings me to ESC’s….


BL Electronic Speed Controllers

The biggest battle ground on race tracks around the world right now, most particularly in the spec classes, is in the area of ESC’s. There are lots of small reasons for this, but one large reason. In a sensored BL system, the ESC controls the “timing” of the motor – when each section of the wire stack is powered up to contribute to the spinning of the rotor (google brushless motors for some proper tech info on how exactly that works).

The first generation of ESC’s (like the Novak GTB or LRP Sphere TC Spec) had some optional power curve settings that changed the timing of the ESC to increase performance, or to make power delivery smoother as required. This is all relatively fine.

The newer ESC’s (like the LRP SPX or SXX Stockspec, Tekin, Speedpassion GT 2.0 and new Novak Kinetic push that one step further, adding dynamic motor timing – meaning that the ESC can change timing on the fly. Low timing at low revs gives maximum torque and smoothest control, but as revs build, timing is increased and performance can be staggering.

Right now, being competitive in spec racing globally depends on having the right ESC (motors are less critical, but still important). This is particularly so in touring car racing where there is always more grip than power. It is less true in offroad generally, and SC particularly where grip is limited.

That might be enough for tonight. if you made it this far….well done. if you made it this far and understood everything I said….even better.

[soniccj5]

Good read, thanks for sharing.

[flipwils11]

Great read, very helpful.