Motor Speed Selection - Printable Version

Motor Speed Selection - Printable Version

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Motor Speed Selection - BAracer - 8th-Oct-20

I have been reading up on proxy GT3 race series around the world. Unlike the UK ones, some of the series have a free choice on motors and motor speeds, and that got me wondering...

On the assumption that you can adjust the gears on a car to achieve a required top speed, what would be the different characteristics felt between installing a 30k / 200 g*cm motor over a 20k / 200 g*cm motor in your slot car?

RE: Motor Speed Selection - Nonfractal - 9th-Oct-20

Jeremy,
You will find lots of discussion and disagreement on this subject.

For me, the base assumption you make isn't right.
Gearing is a factor or Torque, not of RPM.

Two motors of the same GCM rating will pull the same gear irrespective of the RPM at which they top out.
So when removing a King25 from a car and fitting a King30, I would not change the gearing INITIALLY.

However, the reason I change to a higher RPM is wholly down to speed down the main straight.
Yes, I know "races are won in the corners, not on the straight", BUT the main straight is by far the safest place to pass a car in an adjacent lane, especially in open wheel racing.

If you are thinking about a higher RPM motor because your car doesn't have any "punch" out of the corners , its likely that the motor you have is overgeared or is just not a good specimen. Test it!

Some food for thought:
High RPM motors are really only useful on large tracks with long straights.
Is the proxy track large?
Maybe the proxies have no motor restrictions because the shorter tracks means that no advantage can be gained by a higher RPM motor.

I've never raced proxies but it intrigues me. How to set a car up for a track you've never touched?
For me , tuning is a process of continual evolution. Build, test, tune, test, tune, test, tune, test, tune.....
How to do that for a proxy?

You may find that the biggest challenge is not motors and gearing, it's TRACTION.
Getting the right tyres and preparing them for the track surface may well be your biggest challenge especially if it's not identical to your test track or local club track.

So back to your initial assumption:
If you lower the gearing on a higher RPM motor , you put more effective torque to the wheels and this will exacerbate any shortfall in traction that your car has. Increasing torque beyond the capability of the tyres will make the car harder to handle and lengthen lap times.

Alan
(Waiting for the rocks to start being thrown) Bigsmile

RE: Motor Speed Selection - BAracer - 9th-Oct-20

None from me!

In the absence of being able to test on the proxy tracks, I thought the next best thing is to analyse what the gearing was, which then highlighted the range of motor speeds, which then got me curious.

So I'm going to tabulate the numbers to see what the successful cars were running and the less successful ones. and see, if indeed, it was about these numbers.

RE: Motor Speed Selection - BAracer - 9th-Oct-20

And what seems to happen with the proxy is that they tune the cars over the winter, and race them in the Summer, and repeat the process on an annual basis. So same as yours Alan, just a longer cycle.

Hence my challenge to myself to try and establish a robust starting point based on historical data.

But your summary picks up on what I am trying to get my head round...if you gear down a high revving motor for limiting top speed, and consequently up the torque at the wheel, why not go for a slower speed, touquey motor to start with...?

RE: Motor Speed Selection - Mitch58 - 10th-Oct-20

I hosted a round of the GT-3 proxy here last year, most of the cars had 25-30K motors but were geared down to where their top speed was about what you would achieve with most 21.5k motors but with better acceleration and braking.
I enjoyed these cars so much that I built a Scaleauto Corvette to the same specs. I didn't have a 25-30K motor so I used a 21.5 and geared it a bit lower than usual. I could have probably qualified it mid pack, But I could never drive it like that lap after lap. These cars were great. The greatest difference that separated the top of the pack from the bottom was smoothness and drivability rather than just speed.

RE: Motor Speed Selection - BAracer - 10th-Oct-20

Hi Mitch

Thanks for the input. In these 'remote' times, the [HRW] Proxy GT3 offers a vast range of car and performance data. That is too tempting a carrot for someone like me who is at the start of their slot car journey (a bit late in life) as it seems to give out all the clues you need to create a fast car. Obviously I am not so naive that I realise there is also some black art at work on tyres, weight distribution and other little things that people don't shout too much about. But you have hinted at what I am thinking is one of the drivers for motor speed choice...

Does a 30k / 200gcm motor geared down to match the top speed of a 20k / 300gcm motor, provide identical acceleration and braking to the slower motor, or is something else happening that creates a difference between the two?

RE: Motor Speed Selection - Grah1 - 10th-Oct-20

Speaking from the point of some one who has both organised and had a fair amount of success in proxy racing over the years I'll chuck in my views .
DONT be over impressed by hi performance motors

DO make sure your car is easy to drive as not all drivers will have the same skill level

REMEMBER grip is king, if the power doesn't get onto the track the fastest motor in the world isn't going to make the car a winner

RELIABILITY a car that need constant attention wont win

STRENGTH Build your car strong enough to withstand abuse

TEST your car before you send it .

PACK it well

Lastly good luck

RE: Motor Speed Selection - Mitch58 - 10th-Oct-20

Borne,

The two cars being equal or similar the one with the faster motors and lower gears will have quicker acceleration coming out of a corner and better braking going in. Since the typical home track is small and twisty this is a great advantage. On a large commercial type track with long straights and long fast sweeping curves the advantage would be less but you could still run a bit deeper into the corner and be a bit quicker coming out
If you're building something for your home track make it fit that track. If your building for a club race check the specs, they often limit gear ratios and motor speeds to keep the racing closer.
The real key is the handling, weight, balance and most importantly the tires.
For the grandkids I took three of my older Slot Its and put in H&R 18K motors, these have become my favorite cars to flail around the track.
, and make for some very close racing.

Back to the GT-3 proxy cars. On my 70' track anything under 8seconds is considered quick, anything under 7 seconds is fast. These cars were all in the 6s and the top 5 cars I believe were in the high 5s. I qualified them all myself, and the quickest cars were extremely smooth in the corners rather than just faster. The racing was done by three drivers and they all enjoyed them.