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Brushless Slot cars

22008 Views 199 Replies 24 Participants Last post by  Dr_C
Hi All,

I have been looking into other hobbies recently as I saw an RC plane and thought I'd better give that a go too! Anyhow, these days all the electric motors in RC planes seem to be brushless. Is that something that we'll see with Slot Cars in the future? Are there any already?

Obviously they are more efficient and probably more reliable and have less wear, surely that'd be a good thing?

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Brushless motors could go the same way as other changes in motor technology have got into slot cars past.
At first the standard new technology from some other application is applied to slot cars.
That doesn't provide much, if any advantage.
Then guys who understand what makes slot cars work start developing motors specially for slot racing using the new technology.
Extra power isn't necessarily the best way of using new technology - as with previous changes in motor technology slot cars often gained more from lighter, smaller, lower c of g motors than they did from extra power.
Of course just plonking a different sort of motor in an existing chassis isn't usually the best way to get the benefit of the new motor, chassis need to be developed to make full use of the new motors.
Then motor and chassis developments feed on one another to produce a better car.

A gain in efficiency is a huge advantage in planes or cars that have to carry their batteries around with them. In slot cars efficiency is much less significant as long as motor cooling is adequate.
Commutator and brush wear are an issue with brush motors (particularly the quick ones) so brushless would have an advantage there.
Bearing wear would be just as much of an issue with or without brushes.

Will brush less take over in slot cars?
With home set cars, every penny that can be cut from the production cost matters, so the very low production cost of basic brush motors is a big advantage.
With faster cars the customer is prepared to pay more for better performance. Is it worth investing in the development of brushless slot car motors for these? That's a decision for the guys who can afford to make the investment.
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Slot cars have been built with brushless motors.
They did have electronics in the car to switch the dc power from the the normal slot car track between the motor coils.

What advantages were demonstrated?
When track tested using identical chassis etc. brushless powered was substantially slower than normal (brushed) slot car motors (in identical chassis) .
The brushless set up was more expensive than normal (brushed) slot car motors.

Does that mean brushless motors are a waste of time for slot cars?
I don't think so. If a brushless set up more suitable for slot cars were developed who knows how good it would be.
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Lower vibration possibly yes, but is vibration a problem with brushed, I am aware of no problem that needs to be fixed.
BUT is the vibration any lower?

Indeed balancing isn't significant for the sort of slot car motors used in rug racing. These motors are only reving to maybe 20ish thousand rpm which is way below the speed of the quicker slot car motors. Imbalance forces (and therefore vibration) get much larger as revs increase (the scientists among us will know it is proportional to the square of speed).

A basic unbalanced armature of a 3 pole brush motor are often a good deal further out of balance that a brushless motor BUT higher reving slot car motors all come balanced by the manufacturer. Balancing the armature is crucial for higher reving slot car motors, not just from a vibration point of view but also because an otherwise simlar unbalanced arm won't rev to anywhere nears the same speed as a properly balanced one.
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A supplier who makes very fast slot car motors and very fast brushless motors for RC would be well placed to develop brushless motors for the fastest slot cars. They haven't chosen to make brushless motor for slot cars, whatever their reasons for not doing so - the reasons won't be lack of knowledge of brushless technology nor a lack of knowledge about what's need to make a really fast slot car nor a lack of interest in making motors so slot cars can lap even faster.

Spin anything to high enough rpm and something and it will fail. With high end brushed slot car motor what fails first is generally the commutator. On high end slot car motors that happens at somewhere over 200k, but of course it's not a limit anybody chooses to explore. The quickest slot cars don't run at much over half that on track. Would a motor that could go beyond that be a practical advantage in a slot car?

interesting to read that most seem to be thinking of speed, well for digital use only I'm thinking increased reliability is the key reason to look at this topic,
Are you talking about reliability of the whole digital car or just the motor? At the sort of power level appropriate to digital, ordinary brushed motors normally last a long time.

Brushed motors with suppression discs on the armature need less external suppression components. (Come to think of it, wouldn't it be niece to have a comprehensive list of which motors have that feature, afraid I don't have such a list - any offer?)
What about more cars per amp and smaller voltage drops along the track (I.e. more cars and more consistent power)?
Agreed increased efficiency gives you that.

However, is the fluctuation of track voltage a problem in digital racing? Many digital experts seem to be of the opinion that IF the track wiring, connectivity between sections and power supply are up to the job , fluctuation of track voltage aren't big enough to be a problem. For sure there are many posts on how to get good enough track wiring, connectivity between sections and power supplies.

How much of an advantage is less amps for the same power (aka increased efficiency) in digital slot racing? The current needed for a couple of dozen digital cars with brushed motors can be supplied by readily available power supplies, indeed substantially higher current power supplies are in use on some non-digital slot car tracks.

Just supposing fluctuating motor power is the real concern, is there another way of solving it?
While the lower current of brushless motors would somewhat reduce the fluctuations in track voltage, it cannot eliminate it. Some electronics in the car could deliver pretty consistent motor power even though the track voltage was fluctuating. So although we are still stuck with a fluctuating track voltage that doesn't necessarily mean we are stuck with fluctuating motor power. The simplistic approach would be to put an off the shelf linear voltage regulator in the car, but that would add mass and produce heating in the car. Redesigning the control chip to adjust the PWM so the motor delivered consistent power should add very little mass or heat in the car.
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Couldnt you pack more power into a smaller engine package? Might be great for more modern LMP cars.
Much more power in a smaller package than 130 size motors are already available in off the shelf brushed slot car motors.

A major reason nobody uses them in plastic chassis LMPs is that they produce very much more power than those chassis can handle.
Wouldn't it be better to compare the same car with bruhsed and brushless motors in the same position? Changing the motor orientation introduces more variable that might confuse the comparison.

So just to check... if there are long straights with gentle turns the in-line would likely be faster? While if there are lots of winds and sharper turns the sidewider would be faster and less likely to exit the track? Right?
Are you talking about a Scalex 911 RSR slot car or some other make? Perhaps those with experience of that specific car could answer the question.

There's a whole bunch of reasons why the motor orientation might make a difference to performance - for example the motor's position changes the magnetic attraction to the rails: weight distribution: gear ratio: tyre diameter: the efficiency of the gears that will fit : the stiffness of the back end. There is no general answer to which is best for all sorts of slot car or for all sorts of track.
On the subject of very fast slot cars...

When will be the next attempt at a slot-car land speed record...? any photos of the current record holder... was it brushless? what was the max speed achieved (actual and scale)? And over what distance?
When? If and when somebody builds a suitable straight line track. A few attempts to do that apparently haven't got beyond the planning stage, the use of a long enough building and the cost of building a track long enough track seem to have been the main reasons they didn't get any further.

The fastest slot dragsters reach about 130-140mph for a very brief period.

Apparently the closed circuit record is 139.784 km / hr = 86.858 mph. This used a track with two 12 meter straights, one upside down (!), with 180 degree loops joining them.

The world record for a "King Track" is 1.286 seconds for the standard 155ft lap - that works out at just over 82mph average. In recent years the King Track record has been broken several times, most recently in early 2018. Obviously the maximum speed will be higher than the average, but there doesn't seem to be any reliable measurements of how much faster. Here's a video of the record lap
They all use brushed motors and are 1/24. They are all actual speeds.

There are some speeds recorded on long straight "line land speed record" type tracks, these are very much slower than the average speeds round circuits. Some of these times were set with severe restrictions on the type of car. They are records within those rules.

They all use brushed motors

Scale speed is something of a can of worms - it often sparks off a discussion about which of the different ways of calculating scale speed is correct, a discussion which rapidly ascends way of the heads of most contributors. Unless anybody really really wants to rerun that sort of discussion, I reckon sticking to actual speeds is good as it is both easy for everybody to understand and unambiguous.
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What keeps the car on the track when cornering at these speeds?

Banked turns and a lot of aerodynamic down force are big factors. Of course the chassis and tyres make a significant contribution!

For straight line speed records we can be pretty sure there wouldn't be a need for that much down force, therefore you could have less drag and more speed with the same sort of (brushed) motor.
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Hi Sealevel

Yes is a good example of a thread about scale speed.

If there are any new insights about scale speed that would be a good place to post them. For sure a better place to discuss it than a thread about brushless motors in slot cars
I doubt there's much point in re-posting what has already been said.
1/ How much faster than a superfast brushed slotcar motor is a similar sized brushless motor... lets have some speed trap strobe photos please... the benchmark should be a NSR King46 motor... right?
Comparisons between brushless motors with an NSR King46 motor would be interesting, I look forward to seeing the results. So would comparisons with superfast brushed slotcar motor

A King is an example of a "long can" (Mabuchi FK-180 size) motor, These are the largest and heaviest motors commonly used in slot cars these days. Superfast brushed slotcar motors are considerably smaller, around half the weight and rev to several times the speed.
Some while ago the average revs of a superfast brushed slotcar motor in the fastest sort of slot car ( a "wing car") were calculated from the lap time, gear ratio and tyre diameter, the result was.110k rpm. This was only average rpm for a lap, the maximum speed must surely have been higher.

The suppliers of high reving brushed motors warn against free running them at anywhere near full voltage. The problem is they will fail due to excessive revs. apparently the commutator is what usually goes first, figures in excess of 200k rpm are often quoted. Of course the revs in a car don't reach that so comm failures are rare.
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Hi 300SLR, appreciate your insights, what would be a good example of a modern superfast brushed slotcar motor please?

The fastest motors are known a strap motors, this is a generic term rather than a specific model of motor. The armatures are normally specified by the wind, a typical example in the Eurosport class would be 19 turns of 25 AWG wound on a 7.6mm long 12.2mm diameter stack. The rest of the motor often comes from a different maker and would normally have multiple small magnets rather than just one each side.

It might be worth mentioning that these sorts of motor needs to be fitted in a spring steel chassis to provide good handling and cornering speeds with that sort of motor performance., Trying to put one in a proprietary plastic chassis is pretty much a non starter, as has been said these cars can easily be overpowered to the detriment of handling even with much slower motors so there's not a lot to be gained by making them even more overpowered!
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