38 replies to this topic

[Phil Smith]

On Facebook, the European racers sometimes talk about the gyro effect of the motor in sidewinder/anglewinder cars. I've never heard mention of this from any US racers. In fact I'd never heard of it at all until very recently, on the Facebook group "Brushless slot car racing association."

 

They're good, experienced racers. They seem to take it quite seriously. There's no reason to doubt them. And no one ever does doubt them. It seems it's accepted by everyone as fact.

 

So why is it not a thing in the US? I don't think I've heard any of the top racers like Swiss mention it. Or like I said, anyone talk about it.

[Bill Seitz]

Phil,

 

I've seen forum discussions on gyro effect in the past, but I believe it's more theory-based than actual reality. Sure, the forces exist, but my belief is they're so small in a slot car they're inconsequential to the much larger forces that prevail.

 

I've no first-hand experience with brushless motors, although from photos the outrunners being used look like they could have a larger diameter rotating mass than the arms in brushed motors. This may impart an amount of gyro force to be reckoned with that I haven't experienced in my years playing with brushed motor slot cars. It could be a factor, particularly if cars are grip or downforce challenged. But in the majority of the brushed motor slot racing in the US, I think the reason it's not an issue we hear about is because it's not an important issue to slot car dynamics.

 

Weight, weight distribution, chassis geometry, grip, and aero are much more profound and realized effects that swamp what little gyro effect there may actually be.

[Bryan Warmack]

Several years ago I did a test to see if this gyro or torque effect was something that would actually show up in slot car performance. I was running on the Buena Park Flat track and the two motors I used were the Falcon 7 and the TSR D3, Retro motors running in opposite directions that show a significant 'snap' when hooked up to a power supply.

 

I ran them in a decent Retro Can-Am car that had won races on that track, (three turns left and two turns right) and after doing back to back tests on several lanes with virtually no difference in lap times and no noticeable handling differences, I came to the conclusion that despite a real effect with the motor torque, it didn't seem to show up as any kind of handling or driving differences in a relatively heavy slot car.

[Wink Hackman]

I don't believe it's just theoretical - the open classes use strap motors running at over 150k RPM, where the precessional effect of the armature noticeably helps the handling.

 

In an anglewinder, that force has the effect of transferring weight to the inside wheel in a corner, so the car stays flatter.  It will be more pronounced in a fast corner, where the motor is revving most. You won't notice it with low-revving FK motors.  And maybe it's more apparent on flat tracks than banked ones - in Europe banked tracks are scarce.

[NSwanberg]

Hold any car in your hand. Run it at about 8 volts. See if you can feel the opposition to movement in certain directions of rotation. Does it stabilize the car or does it make it harder to turn? Compare anglewinders, sidewinders and, inlines.

 

My head hurts... again.

[Eddie Fleming]

I think the gyro effect is a part of why anglewinders handle better than inlines.

 

Beyond that the effect is so small and so overridden by other forces we have more control of that it is not worth worrying about.

 

IMHO.

[bbr]

Angular momentum

[Phil Smith]

I don't believe it's just theoretical - the open classes use strap motors running at over 150k RPM, where the precessional effect of the armature noticeably helps the handling.

 

In an anglewinder, that force has the effect of transferring weight to the inside wheel in a corner, so the car stays flatter.  It will be more pronounced in a fast corner, where the motor is revving most. You won't notice it with low-revving FK motors.  And maybe it's more apparent on flat tracks than banked ones - in Europe banked tracks are scarce.

 

This is the type of thing I've been reading. Here's a recent Facebook discussion about it.

[Bill Seitz]

Joel Montague once told me that 150,000 RPM in a slot car motor wasn't possible, that the hottest winds only ran about 105,000 RPM. This seems plausible, because the ball bearings used in slot car motors are only rated to about 100,000 RPM, so I'd expect a very short life at 50% above that. To attain this RPM, the armature has to be small diameter and low mass, which in itself reduces gyro effect. Considering that flat corners are typically not negotiated at full throttle, the effect is further reduced by a much lower RPM, and the angular chassis displacement is also relatively tiny. This is really not a concerning force. If it were a practical benefit, we'd see development of larger motors to gain more effect rather than the advance of ever smaller ones. Center of gravity seems to be the larger concern over producing gyro effect.

 

Keeping the chassis flatter in a corner may actually be the wrong thing to do. The live rear axle in slot cars is most similar to the arrangement in racing karts. In karts, the chassis setup purposely allows the inside rear wheel to lift on corner entry to reduce the understeer caused by the locked axle. Since the inner and outer wheels need to turn at different RPM to negotiate the turn, reducing grip on the inside tire prevents other skidding/hopping tendencies needed to allow the wheels on a fixed speed axle to get around a corner. It's also well-known in racing cars that the outside wheels provide almost all the grip in corners, which is why suspension geometries are designed to keep the outside wheels as close to vertical as possible regardless of what camber this presents to the inside wheels. I believe slot cars should adhere to these same grip physics. Slot cars also benefit from power-sliding in corners. This also helps with the problems induced by both wheels locked to the same RPM, and it keeps the forward force on the guide more tangential to the corner arc which reduces side load that will cause the guide to lift out of the slot.

 

In terms of the difference between inlines and sidewinders/anglewinders, here again there are multiple factors, not the least being the higher efficiency of the pinion and spur over pinion and crown. Weight distribution also plays a factor and likely also that the typical body can generally be mounted lower over an anglewinder/sidewinder configuration than over the inline. I've played with both chassis configurations and they can be really close, but the anglewinder has that small edge that I've yet to fully discern. Perhaps that's the gyro effect at work, but slot racing hasn't really done anything to tune or enhance that force other than the motor arrangement.

The reality is, slot racing development has actually gone in the opposite direction reducing gyro effect.

[MSwiss]

105,000 RPM??
 
That's way, way too low.
 
At the Jackson 500, in 1992 or '93, Boogie borrowed a radar gun from the Jackson Police Dept. In qualifying, he pointed it at the end of the straightaway.
 
IIRC, I hit 87 MPH, Buddy Buchanan from Camen hit 88, and P.A. Watson, who I think TQ'd, hit 90 MPH.
 
90 MPH.
 
(90 miles) 5,280 ft x 90 = 475,200.
 
475,200 x 12 (inches) = 5,702,400 inches per hour.
 
Circumference of the tire: .770" x 3.1467 = 2.423".
 
5,702,400"  /  2.423" = 2,353,446 rotations of the tire to go 90 miles.
 
8/39 ratio (most common back then).
 
39 / 8 = 4.875.
 
4.875 x 2,353,446 = 11,473,049 revolutions of the armature required to go 90 miles.
 
11,473,049 / 60 (minutes in an hour) = 191,217 rotations per minute or approx. 191,000 RPM.
 
Here's an old link where I quote 188K. I may have used .760" or .765" as the tire diameter.

Differenet blue motor?

[Mark Onofri]

That's just one of the many reasons you are a champion. I've been wanting to write that formula for a while. Thanks

[Bags]

I wouldn’t trust a radar gun for anything to do with speed.
 
A Police Radar Makes Mistakes
 
Radar Measures a Tree Speeding

[Phil Hackett]

Mike is right... the open motor speeds are incredible and it's a miracle they last as long as they do. I have shown the open motors to engineers and explain their capabilities and they all say "it can't be done"... hahahaha... 

 

All you have to do is the following:

 

(conservative numbers)

 

1,200 laps in 40 minutes = 30 laps/minute

 

Each lap = 2 seconds (again conservative number and uncompetitive in world-class G7)

 

Track length = 155ft... 155ft/2seconds = 77.5 feet/second (for 40 minutes)

 

A nominal tire dia (no one knows the actual tire growth, if any, at speed) is .765"od OD... which = 2.40" per revolution of axle...

 

Using the 8/39 gear ratio above... the motor needs to spin 4.875 times for each axle rotation...

 

Now for the fun: 77.5feet/second = 930 inches/second = 387.5 axle revolutions/second

 

387.5 axle revs/second x 4.875 is 1,889 motor revs per SECOND...

 

1,889 x 60 (ya know... 60 seconds = 1 minute) = 113,434 RPM *average* for *40 minutes* which is pretty fantastic.

 

So the 191,000 that Mike posted is most likely low for today's G7 cars.

[Eddie Fleming]

I don't remember the details but the story was that Champion talked with Georgia Tech on motors in the 60s and GT said that theoretically a three pole motor could not turn over some number of RPM. At the time Champion was turning way over that number so the conection to GT did not last long 

 

Any body remember the details of that story?

 

Or did I dream that?

[Mark Onofri]

Phil,is there a quiz afterwards?

[Bill from NH]

No quiz, just a math exam for you!    

[MSwiss]

I'm pretty sure gyro effect is a thing.

I was skeptical at first, but the Eurosport guys who really jump through hoops to achieve it, are ultra serious slot racers.

There was a video of Lee Gilbert trimming down the end of an arm shaft to 1.5MM, for a 6T pinion, running the motor on a power supply and using a Dremel tool.

For him to do stuff like that, he had to be real convinced the added gyro effect aided the handling.

If it was just a matter of having instant acceleration, you could do that with arm wind and timing.

In some of the 1/32 cars, they have gone to a 1.2MM shaft so they can use a 5T pinion.

My experiences, I remember trying to use a B Production car that Manta Ray had left me, that had an 8T pinion, for an event at my raceway.

I thought it ran well until I tried someone else's car with a 7T.

It was slower on the straightaway, but probably at least .2-.3 faster around the car.

2 different cars, but it was still real convincing.

This thread jogged a wing car memory of mine, probably from about 1997 or 98.

On a lark, because Koford started selling a 7T pinion for Eurosport/scale racing, I tried one for the heck of it, with the most unlikely wind for it, a 94.5.

It had no bank speed, but it whistled around the infield, and I used that motor, parts of a couple big races I won.

A friend would ask "What's with the sound of that motor?"

I fed him some BS he never bought, and when I ran it, he would always say "You're running that Highwinder, aren't you?" Lol

The thought was to use it for a Purple, Black, Yellow, with the shorter trip to the Deadman, but a long way around the Donut.

But the car handled so well, I started using it on Red.

At a race in Alabama, I remember going into the 90,and hearing the guy next to me on White spinning his pinion in the Donut.

I had zero chance to stop and knew I was screwed.

My driver side rear, clobbered his stopped car, the spur gear lasting just long enough, that I made it back to the panel, quickly replaced it, and still won the race.

I then abandoned the 7T pinions because I was worried the more "starry" shape was at least a bit harder on the spur gear.

Back then, it never occurred to me that the reason it seemed that car couldn't be driven out of the slot, was the added gyro effect of the 7-38 gearing.

[Wink Hackman]

Seconding what Mike says, one of the classes we run at my club is OG12. I've tried identical motor setups except for gear ratio - choice is either 7/42 or 6/40.  With no other changes to the car, the 6/40 wins every time.  There's no doubt that the more the motor revs, the better the handling. Having said that, it might not all be about gyro effect - it could also be that the motor is just more driveable higher in the rev band, but I reckon the gyro effect plays a part.

[MSwiss]

Wink, you would think the added punch would make the car harder to drive, but once you get the controller settings where it's comfortable to you, the car is faster in the turns.

[Dave Crevie]

When I was Eurosport racing I used to check my motors at work using a laboratory vibrotach. I had several .459s that checked at close to 140,000 RPM.  

[Mark Onofri]

In the mid to late 80's, we had a pretty serious oval series going. The comments about the revs brought back some memories. I used a ~=.2 ohm ext. Resistor controller,G-27,G-7ish. I'd disconnect the break or, wrap wire around a Bud can (for a choke). With this setup I was able to keep the motor wound up, for the most part. It really made a difference. Never thought about the gyro effect.
In some English(?) Blog, I saw a car that actually had a flywheel type gyro. It was on a counter shaft,I think. I'm also convinced that the aluminum "heat sinks" are more of a counter balance than heat dissipator.

[Bucky]

Im not very familiar with the effect, but if it factors into slot cars would there be a benefit to getting the armature as close to parallel to the axle as possible? My thought is that the impact would be closer to equal when turning left or right.

[Wink Hackman]

Here is the flywheel giro car - actually two cars, one anglewinder & one inline motor - referred to above:

https://www.slotcarr...story/gyro.html

Built by Gary Fletcher, who I raced with regularly in the 80's.

[Eddie Fleming]

Not following the subject closely but I get the impression that getting and keeping the RPMs up is a large part of optimizing the effect.

 

Question?

 

Is that why the retro stock cars often run better with 10T pinions?

 

Or are those motors to slow and the cars to heavy for it to have much effect? 

[MSwiss]

I think in the case of Retro Stockers, it's a matter of reducing the top speed of a narrow car.
 
At a recent race, Dom Luongo tried 9-26 vs. 10-27.
 
He said lap times were only .05 slower, but the car felt way more settled.
 
Regardless, I don't think the gyro effect applies as much to inlines.
 
Going to the CR102, and using a radically lower numeric ratio, hasn't "stopped" the cars from handling.
 
BTW, here's an interesting comment from that flywheel link.

 

The gyroscopic effect of an armature in a conventional sidewinder or anglewinder tries to stop the car tipping over in corners.

 

The gyro car produces larger forces trying to stop the car tipping due to the additional flywheel rotating at high revs in the same direction as a sidewinder armature."

 

The effect on the chassis  in cornering is rather similar to lowering the centre of gravity.

 

I guess the obvious question is does it lower the CG enough to compensate for the extra components added to the car?