Get another 2G from your SCX RX motors

Squeezing out those last few tenths

Get another 2G from your SCX RX motors

Postby wixwacing » Mon 25 Aug, 2008 11:26 pm

I have recently acquired a couple of new (second hand) SCX models and in pursuit of some extra revs I carried out a simple trick that all us locals should now be using. That is the process of 'skewing' the brush holders in the direction of rotation. This retards the comm. timing and in doing so increases the motor rpm. There is a slight trade off, with torque being marginally reduced, but SCX RX type motors have torque to spare on high current power supplies (5 amps plus)! Skewing is carried out by firstly, removing the motor from the model. Then, using a pair of small jumper leads with crocodile clips attached, run the motor flat out in its normal direction of rotation. Next with a small pair of pointed pliers, grip the brush holder (while the motor is running) and 'skew' the holders in the direction of rotation one at a time. You will noticeably hear the engine rpm increase and when released the revs will subside. The trick is to bend the brush holders sufficiently past the optimum point so when they are released and they spring back; it is to the optimum position. This has to be done carefully as over exuberance will see the edge of the brush holder dig into the comm. material (says the voice of experience). Do this to both holders alternately until the motor revs no higher.

Nothing new here I hear you say. Maybe not to us old lags but a good few young people could benefit from re timing an SCX motor. But wait! That's not all!! Listen on. Whilst having reset one motor on the weekend, I was still a bit disappointed by its persistence to vibrate quite pronouncedly (is that a word??) So, being ever vigilant and thinking outside of the square and wanting to push the envelope and a whole host of other clichés, I thought to my self, 'If only I could balance an arm without stripping a motor’, or at least go some way towards it,? Well, I kid you not, what happened next was a revelation.

At this stage, Paul Stevens, avert your gaze! You already have too many of my secrets!!

Being a 'back woods' kind of boy (many years since from the heart of rural London) I have always had a little pocket sharpening stone which over the years has been used to sharpen pen knives, darts, modelling knives and a host of other pointy and sharp objects. It fits comfortably in the palm of the hand and is of concise rectangular dimensions, being long and thin and flat. I noticed on the errant motor that the armature segments were a bit higgledy piggledy as if the centres where eccentric. I wondered? If I ran the motor and carefully held the flat narrow end through the opening in the motor, would it grind it flat, or to a better shape at least. So, holding the fast running motor in one hand, I gently applied the stone to the armature segments. Did my ears deceive me, did the motor speed up?? Surely not! I tried again and there was no doubt, the motor gained some useable rpm! Looking at the stationary arm I could see that the stone was taking the high spots off the poles. More on one pole than the others.

I persisted, occasionally dunking the running motor in a bowl of water to remove the filings. Sure enough, application after application, the motor was getting faster and faster!! And the poles were getting shinier and shinier and best of all!! The motor was getting smoother and smoother!! Huh! The end result was a motor with silky smooth speed and along with the comm. timing it must have gained considerable rpm. Its emitted scream was now higher than a good Scaley motor and almost at NC5 pitch. So what has happened?

The theory as I see it.

Firstly, the armature was obviously out of balance. This was caused by the poor alignment of poorly stamped armature segments. The vibration in itself was enough to noticeably reduce top revs. The process of grinding off the pole pieces aided its balance and allowed a degree of rpm increase but it is my belief that the overall motor speed was enhanced by increasing the air gap between the magnets and the poles. DC motor dynamics dictate that a close magnet gap or 'shimmed' magnets will increase motor torque but reduce motor rpm, this is a fact. Motors with increased torque are better able to use lower gear ratios.

ie. standard motor 'X' uses 3 : 1 final drive ratio for model weighing 'Y' grams for optimum performance 'Z'.

but

shimmed motor (X + a) uses 2.7 : 1 final drive ratio for model weighing 'Y' grams for optimum performance (Z + b)

Where 'a' = closer air gap and 'b' = model speed increase.

So what has this to do with the price of spaghetti? Simple. By increasing the air gap I have reduced effective flux density acting on the armature (magnetic flux is governed by the law of the inverse square). This will result in a small decrease in torque but will induce an increase in rpm! The SCX long arm RX motors already have heaps of torque when run on at least 1.5 amps supply and a slight loss is neither here nor there. To some degree it is beneficial as surplus torque will have been expended as wheel spin anyhow. But the still usable torque, coupled with the increase in RPM, should (WILL) cause the model to be faster to the tune of the rpm increase. In turn the model will

A. Be a lot quicker without too much reduction in acceleration and

B. Be a lot smoother to drive through and out of corners as the sudden torque and consequent whiplash effect have been reduced.

Possibly theory but all a bit 1984 (sorry kids, a George Orwell novel). I have officially named it the "Wix configuration" or 'Wixation' (add that to your spell checker) for short, a name to be used on all future occasions.

So, firstly, if you race in South East Queensland, please don't tell anyone about this, especially Paul, and secondly, if you do try this out, you aren't allowed to race it against me!!
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Re: Get another 2G from your SCX RX motors

Postby Buzzard » Mon 15 Sep, 2008 8:32 pm

Sorry Phil,

You forgot to mention that it only works where you have an open can motor with open brushes. :wink: ...

Not much good for us with 5 thumbs on each hand. :oops:

After the race meeting last weekend, I agree that it is totally usable on SCX motors,
but Ninco or Scaley motors require a lot more fiddling. :idea: :idea:

Mayhap you can educate us on how to get Scaley to over perform without taking the motor apart.
Cheers
Kev.

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I enjoy every minute.
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Re: Get another 2G from your SCX RX motors

Postby wixwacing » Mon 15 Sep, 2008 9:11 pm

Hi Kev,

The moral to the story is:


Don't faf about with all that expensive stuff. whip em with a cheapy.... then rub their noses in it!!!


The Aston Martin DBR GT I raced on Saturday has a wixwacing blue printed motor!!


I agree with what you say though, it's a pity all the rest aren't accessible, but then there'd be no challenge!
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Re: Get another 2G from your SCX RX motors

Postby wixwacing » Thu 30 Oct, 2008 11:03 pm

Further to this topic, I raced Legends at Graceville last weekend. My Ninco Subaru had a motor transplant before the event because I have suspected the old NC2 for some time. I intended to give the NC2 some 'Wixation' but the motor isn't vented!! I had a new NC5 which I installed and cut the foil rapper on one of the vents. The arm got a light honing and the revs surely increased.

Now, before you start screaming foul! I have to point out I was not the fastest car on the track, nor did I win the event, but the model certainly went well!! I'm looking forward to its next board track outing!!!
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Re: Get another 2G from your SCX RX motors

Postby wixwacing » Sun 09 Nov, 2008 7:08 pm

I raced a six year old SCX Astra DTM at the Eggdome this week, complete with blueprinted Pro Turbo motor and got second by two seconds after twelve minutes racing!! Mind you, I was giving a few years away to the winner, but the motor was a blinder!!
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Re: Get another 2G from your SCX RX motors

Postby yankfaraway » Mon 10 Nov, 2008 3:14 am

I've read about this several times, and I have yet to see an article that includes photos. Can someone take a picture and identify what we're talking about? I think I understand it, since I have several adjustable "Rotor Motor" cars, but they are just way too much power, and the SCX idea looks very good in my applications.
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Re: Get another 2G from your SCX RX motors

Postby wixwacing » Sun 16 Nov, 2008 12:10 am

HI Rob

I'll try and get round to some photos soon.
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Re: Get another 2G from your SCX RX motors

Postby paulthetexan » Sun 16 Nov, 2008 8:35 am

Howdy

Just a quick questions with regard to local racing rules and regulations and the spirit of freindly competition .

If you start with a pro-turbo @ 18,000 , then adjust the timing , then balance the arm' , then add 2000 rpm = 20,000 rpm
is it still a standard motor and does it satisfy scrutineering ?

This question has been put to me by other members of the group who feel there is an unfair advantage to be had .
It would be intersting to actually measure the change in rpm through the tuning process , as the drivabuility is easily noticed by the seat of the pants so to speak .

Apart from these obvious concerns , I must admit after taking up the offer to do a couple of laps with your tweaked DTM , the performance was impressive .

Regards
Paul
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Re: Get another 2G from your SCX RX motors

Postby kenneth » Sun 16 Nov, 2008 8:20 pm

Good question Paul.
Who does scrutineer the scrutineer??? hmmm .
Phil & his `standard` motors. :wink:
If an SCX Pro Turbo is rated @ 18k rpm out of the box, and we all know some are better and some worse, but i have seen independant tests of the pro turbo measured between 18.5 to 20.5 k rpm OOTB ( for differet motors - some tested at over 20k staright away)@12v then the `wixation` of the motor would take it to over 20k min. up to 22k .
is 22k rpm accepted in a 20k capped class??? :wink:
`It is better to enter a turn slow & come out fast, than to enter a turn fast & come out dead` Ferry Porsche
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Re: Get another 2G from your SCX RX motors

Postby Cyph » Sun 16 Nov, 2008 8:49 pm

At least we can look at it this way, Phil hasn't kept this behind closed doors of his workshop. It is out in the open, people know it can be done. We aren't racing for sheep stations after all.

It's out in the open, we can discuss it, and figure out how to approach it.

More can be said for the results of DTM at Eggys the other weekend in consistent driving compared to having an extra bit of RPM out of an SCX motor. The fact Paul and Phil both finished a whopping 30 seconds in front after 100 laps (so, about 5 or so laps better off than the rest of us), says a lot for their driving, and more than likely getting in good heats and not getting affected by people deslotting in front of them, or deslotting themselves.

It's amazing how much time you lose when someone comes off in front of you, manages to take you out as well, and you end up losing time, but that's racing for you.
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Re: Get another 2G from your SCX RX motors

Postby kenneth » Sun 16 Nov, 2008 10:27 pm

well i was taking the P!$$ - my post wasn`t meant to be taken seriously.
who would take me seriously anyway :)
`It is better to enter a turn slow & come out fast, than to enter a turn fast & come out dead` Ferry Porsche
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Re: Get another 2G from your SCX RX motors

Postby wixwacing » Sun 16 Nov, 2008 11:40 pm

G'day guys,

All very interesting and an example of how hard it can be to maintain parity on the track. The exercise in question was more an exercise in getting a bit more performance from probably one of the most popular makes of slotcar. If you add up all the slotcars sold from not only the dedicated slotcar sites but from the 'Mr Toys' Toy world and other hobby stores, I would not be surprised if SCX account for fifty percent of all slotcars sold in Australia. I called in Hobby One last Thursday evening to pick up some other hobby supplies and they have already stocked up for Xmas. The corner of the store is waist deep in Scaley and SCX products.

Having said this it is noticeable in a lot of other circles how little SCX achieve as far as results are concerned. Their motors are so inconsistent as far as state of tune is concerned that only one in twenty are able to compete. The term 'blue printing' does not infer a modification; rather, it implies that the motor has been brought up to its design specifications from an otherwise rather poor level of tune. To bring a motor up to the spec of the ‘1 in 20' is blue printing. To make a motor quicker than the '1 in 20' is tuning!! As with Fly, Scaley and Ninco motors, there is a subtle difference. I have watched guys swap 'hot' Ninco, Scaley and Fly motors from one model to the next for race purposes at race meetings! They are taking advantage of a 'one in twenty' motor to make themselves more competitive.

Buy blueprinting an SCX motor you remove the need to swap motors from one model to another. Those that have raced against my blue SCX DTM Merc will know that out of its box it is as fast as a Fly car. I could swap that motor from one model to another ‘til the cows come home, race after race, and that shouldn't be a problem. To bring a similar motor up to that spec (not beyond) therefore must be acceptable. If not, then swapping motors from one model to another must also be disallowed, and how would we police that??

Next, knowing the frailty of SCX motors, I argue the point that most SCX Pro Turbos and RX42B's DO NOT run at their advertised specification!! In fact, it is my view that they run at well below it because of their poor assembly, therefore, when I state "Get another 2G from your SCX motor" it is purely a method to bring them to their advertised spec. Hands up all who think the RX Pro Turbo runs as fast as a Fly motor?? Anybody??, Nobody?? Yet the Fly motor is rated at 18.000rpm @ 12.0 volts and the SCX motor is rated at 19.000 @ just under 14 volts!!

The real problem starts when people see their Fly and Ninco cars beaten by an SCX car. Not buy a tuned motor but by a standard spec SCX motor! The problem doesn't lie with the motor, it has its roots elsewhere and regardless of which motor is doing the business, if the 'other' aspect of model racing is below par then we can't expect a change of motor to fix it. The sooner we come to terms with that the better. To help a motor to achieve its designed potential is not a crime, it just minimises motor swapping! A motor who's spec is openly advertised to be as quick as an NC5 should be allowed to achieve that potential. After that it is up to the driver!

If I were to race Ninco NC5's and Fly motors then I would expect marginally better results than I achieve with my blueprinted SCX motors, would we need then to be concerned about NC5 and Fly motors?? This is an age old debate which locally, goes back to the turn of the millennium and people then had a problem being beaten by an SCX model! The blueprint techniques are there out in the open, anyone can use them AT NO COST! So do yourselves a favour and blueprint an SCX motor today!
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Re: Get another 2G from your SCX RX motors

Postby Cyph » Mon 17 Nov, 2008 8:00 am

kenneth wrote:well i was taking the P!$$ - my post wasn`t meant to be taken seriously.
who would take me seriously anyway :)


Often hard to tell with forums and written word! :)
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Re: Get another 2G from your SCX RX motors

Postby paulthetexan » Mon 17 Nov, 2008 9:11 am

Howdy

Its interesting to not that so much concern is placed on motor spec. when you consider that our group mostly race on small board tracks . I could understand if we were magnet racers then motor performance would be more of an issue , the same reason we don't race slot.it on magnet , to many differing spec motors .

I've tuned a lot of cars over the last couple of years but I must say I don't usually give the motor a second glance . There is so much more to getting a car to go well , like tyres , guide , weight and where to put it .

One very interesting point to consider is that I was fortunate enough to win the DTM event running against Phil while I drove 2 different scaley's with standard tyres and in one heat I drove an SCX Astra with standard tyres and no weight with an RX41 motor.
On more than one occasion I ended up in the same heat as Phil and raced head to head and side by side for many laps with a standard scaley . Eventually Phil bailed and left me to carry on alone , ( he must have blistered a tyre or twisted an axle , to much horse power you know ) .

Anyway , I do think that the front runners will finish as front runners no matter wich car they are driving, be it Ninco , scaley , Fly , Carrera or SCX .

We should spend more time tuning our cars , more effort driving steady enough to stay on the track , and less time worrying about the guy next door .

After all , its an enjoyable hobby designed to get people together so we can drink more beer and have a BBQ every now and again.
You now blokes can stay at home and listen to the kids argue and fight over who's got the best toys to play with !

Next time we see something a bit suspect how about openly heckeling it in front of the crowd ( in a light hearted kind of way of course ) to at least draw attention to it in stead of quietly grumbling in the hall ways . There are too few of us Slot Car Fanatics to be upsetting each other with minor issues that don't really amount to the end of the earth .

Hey Phil , when can I pick my hotrod motor up , I'll have mine at 28,000 !!!!!!!!

Regards to all
Paul
Last edited by paulthetexan on Mon 17 Nov, 2008 6:41 pm, edited 1 time in total.
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Re: Get another 2G from your SCX RX motors

Postby kenneth » Mon 17 Nov, 2008 10:22 am

I`ll just get my coat then !
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