Gravity class insights

Talk forum for HO scale slot cars. 1/87 and 1/64 scale.

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Re: Gravity class insights

Postby slotking » Thu May 08, 2014 11:06 am

Real sports and formula racing cars are built to come in below the minimum weight allowed by the rules. They then add ballast,


I read where 1 team did that back in the day, but the added weight would roll out of the car on the turns
not sure if it was true or not?
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Re: Gravity class insights

Postby slotking » Thu May 08, 2014 11:09 am

Not all reed switches are created equal. If you are having trouble tripping the reed, swap out the reed for one with greater sensitivity.


very true
plus they have to placed correctly.

I have been on tracks where t-jets counted just fine and unlimited inlines did as well
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Re: Gravity class insights

Postby jpennington » Tue Jun 03, 2014 2:52 pm

On April 4th Al posted about the concept of ballast weighting your cars. One of my more successful cars was built along these lines in 2012. It utilized .015 brass instead of the usual .032, which brought the overall weight of the car down to 11 grams. Then .020 tungsten was strategically added, along with some lead to bring the weight up to 18.5 grams. As you see Al's car weight was added to the middle along the line of thinking of traditional full size car philosophy, whereas mine was added to the extremes to increase the polar and pitch moments of inertia. Now there is the debate - are slot cars and full size cars following different principals there? No body questions lower center of gravity benefiting both, but what about inertial placement? Of course the track will always answer the question regardless of the racers thoughts!

Hope to meet some of you at the Nats Gravity support race on Wednesday. Scott Terry is working hard at completing some very impressive angle winders that will be for sale. The prototypes have gone quite fast on his track. And for those of you who want it they use pickups!

Joel
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Re: Gravity class insights

Postby Fingerracer » Wed Jun 04, 2014 11:51 am

Joel, the closest 1:1 vehicle that a slot car would be similar to is a go Kart. Full size race cars having suspensions of various types have to deal with the problem of sprung weight versus un-sprung weight when considering the proper placement of ballast. I would like to try a Gravity car at the Nats but will have to see what my budget is like as the harsh winter in Pa. has me traveling to the Nats on a " shoestring ". I look forward to competing in or spectating this race.
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Re: Gravity class insights

Postby jpennington » Mon Jun 09, 2014 10:37 pm

Pat Dennis has some interesting insights that he gave me permission to share on similarities and differences between real cars and Ho cars. Pat has a life time of experience in both worlds. Here is what he says:

"Regarding Al’s comments, the similarity between a real racecar and a slot car stop after the fact that both have four wheels and a propulsion device.
An analysis of both follows:
Real Racecar
• An actual racecar has a functioning steering system and a decision-making on-board driver.
• Is operated within the limits of adhesion in the horizontal plane through the experience (through intensive practice) and the “seat-of-the –pants” feedback. Exhaustive studies have proven that a driver who can maintain the smoothest transition of acceleration, braking and sideload G’s turns consistently faster lap times.
• These limits of adhesion are derived through engineering of the car - suspension control, braking design and materials, and tire technology. Additionally, aerodynamics which impart down force enters into this.
• Actual race courses are typically glass-smooth, with somewhat gradual elevation changes
Slot cars
• A slot car follows the dictates of the slot and a remote operator that only controls the power, and is totally dependent on maintaining the guide pin/blade penetration into the slot.
• There is a peculiar force, unique to slot racing that occurs when a slot car is subjected to a curved section following a straight. The front end of the car is violently jerked to one side upon entering the curve - remember that there is no lead-in to the radius, no ability for the driver to "set" the car's suspension upon entering the curve. This is what I referred to as a "spike force" acting on the guide pin/shoe. In a conventional race car this would be roughly equivalent to have the car struck on the front corner by another car at a great rate of speed at nearly right angle to the direction of travel. In an attempt to reduce the effects of this "spike", the TycoPro used a guide flag with a slight lead-in to attempt to "set" he car before that force arrived at full force. (note that the guide flag has the blade extending ahead of the pivot shaft).
• Additionally, the upward force of the pickup material (spring-loaded rigid “skis or flexible contacts, braid, etc.) needed to insure electrical contact adds to the upward force of the front, lifting the guide device.
• There is an additional force consideration, and that is the action/reaction of the pinion gear attempting to "climb" the crown - lifting the front of the chassis on acceleration and under power. This force is reversed upon deceleration - effectively forcing the guide flag/pin downward. This is the reason that an HO car responds so well to a short "off" to the controller approaching the curve. This is as close to "setting" the car for the curve as is possible for a slot car
Note that this forward weight transfer exists in a real racecar, but is much less critical.

• Slot track courses are, in scale, much less smooth and contain a very crucial difference – the contact rails! Crossing these rails (which have significantly lower coefficient of adhesion) unless a tire is sufficiently low durometer to allow deformation only in the rail area will reduce the contact area of the outside tire enormously, and tend to “tip” the inside tire, reducing its contact patch.
• Set-type track systems have additional deficiencies – section-to-section height variations, slot irregularities at the joints and, worst of all, molded track slots have a draft angle, meaning that the walls of the slot are parallel to the track surface – leaning “outward” which tends to eject the pin/blade under cornering forces.
To counteract these negatives, a successful slot car design should incorporate the following design criteria:
• Weight should be concentrated on the rear tires – for maximum traction, and the guide pin/flag to maintain slot penetration during directional transitions. Polar moment is not a factor in slot race car design.
• Testing should be performed to ascertain the optimum opening angle between the guide pin/blade and the contact patch of the rear tires (i.e.: wheelbase and rear track width).
• Overall weight – using a variation of Newton’s First Law – a body in motion tends to maintain that direction, unless acted upon by a second force. The less weight that needs to be “redirected” – as in a car transitioning from a straight into a curve, the less resistive force to that transition will be met
• Tire designs – this should incorporate testing of the inside radius of the rear, to minimize “tripping”. Durometer to compensate the rail intrusion. Coefficient of friction to minimize the sliding of the rear and stay off the rails and, of course minimizing power losses through wheelspin.
A bit of history:
Back in the "dark ages" of 1/32 scale racing in the early 1960s, there were several chassis designs which had the front assembly (wheels & axles and the guide shoe) mounted on a horizontal pivoting device, much in the same manner as he describes. This proved to be ineffective, and the general designs of the day gravitated to a pan with carefully located weights to keep the shoe "planted" in the slot. Further designs involved molding the vertical pivot of the flag canted forward at 100, causing the shoe to lean in such a manner as to counteract the chassis "roll". Although initially effective, it was, again superseded by flat pan & weight system. The "war" over whether a guide flag was superior to the pin raged - and consensus was that this was dependent of the overall track design. The most effective development was mounting the body in such a manner as to allow independent motion from the chassis - additionally counteracting the transmission of resonant vibrations created by the drive system and amplified by the body."
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Re: Gravity class insights

Postby slotking » Tue Jun 10, 2014 12:35 am

LOL

I have been saying that for years!!
mostly when t-jet only folks say that running them is more like racing a real car! :shock: :lol: :lol:
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Re: Gravity class insights

Postby neorules » Tue Jun 10, 2014 9:40 am

Its exactly like running a real car, Except totally different!
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Re: Gravity class insights

Postby jpennington » Wed Jun 11, 2014 6:47 pm

Pat Dennis had some follow up to his earlier comments:

"Additional comments:
Tire Durometer.
During the testing of materials for the TycoPro Performance Kit rear tires, we discovered an unusual problem with too soft material. These induced what the Can Am drivers of the late 1960s described as “tire shake”, where the car would suddenly experience “hopping” at speed. This was diagnosed as one or both tires momentarily losing concentricity as the soft material was distorted by centrifugal force. Therefore there is a lower limit on durometer.
Further amplification of the effects of the “opening angle” formed by the guide pin/flag and the centers of the rear tires.
We conducted a series of tests between otherwise identical cars (motors, tires, chassis set-up and front & rear track dimensions) by altering the wheelbase and guide flag dimensions
Shortening the wheelbase & flag dimensions (opening the angle) yielded a more responsive “turn-in”, but increased the tendency to spin on the vertical axis.
Lengthening this dimension (reducing the angle) seemed to result in a less sharp, but more stable turn-in. The negative was an increased tendency to roll on the longitudinal axis and deslot.
Weight distribution advances.
· By utilizing the “small motor”, the heaviest single component of an HO car is substantially reduced – with another benefit of a lower CG.
· By mounting this “small motor” in the “sidewinder” position, this mass is now placed in a more optimum position for traction weight, minimizing the necessity to add additional weight to the rear of the chassis."
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Re: Gravity class insights

Postby jpennington » Wed Jul 02, 2014 12:08 pm

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We just had a successful support race at this years Nats with 21 entries. The top four were as follows:
1 Doug Morris 94 laps AFX
2 Tim Miller 91 laps inline Landshark
3 Joel Pennington 90 laps custom sidewinder
4 Mark McVittie 90 laps AFX

As you can see the racing is close and the cars are diverse. Doug certainly handed us a driving lesson with an old school car. I will try to get pictures soo of these cars.

On another note the HOPRA senate approved to adapt a set of rules for the gravity class that will be appearing soon. This takes this racing class one step further in its National credit ability.

Scott Terry debute his new semi production angle winder at this race with six of the entries running one. Peter Barclay was able to finsh sixth with one, not too shabby for a brand new platform. Contact Scott if you are interested in one of these.

As you note for those of you who are wiper phobic this car feature pick ups. It also disassembles with tools and not a soldering iron!

Joel
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Re: Gravity class insights

Postby jpennington » Fri Jul 04, 2014 11:14 am

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There has been some interest expressed in seeing the pictures of the gravity cars so I will give pictures and break down of the top four at the Nats support race. Fourth was Mark McVittie with 90 laps, a fast lap of 7.17, and a median best of 7.41.
Mark car was an AFX with:
Arm - Quad lam 210 turn 36
Gearing - 24/11 cluster with an 18th crown
Pan - Full TCP using wipers
Body - BSRT Peugeot
Magnets - Super II

Mark drove a steady race from the B main and only narrowly missed third overall.

Joel
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Re: Gravity class insights

Postby stez1970 » Fri Jul 04, 2014 4:29 pm

Joel,
Thank You for all the information you have been provviding. I'm hearing that the Gravity Class was a great success. I was at Rob Hayes home in Cambridge last Wednesday night and had an opportunity to speak with John Reimels who was quite impressed with the cars and driving skills of the Gravity Class participants. I know that he can't wait to get his solder iron out and try some of the things on his car that he was shown at the race. Again thank you for all the work that you and the other participants did to make this event work so well.

John S.
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Re: Gravity class insights

Postby jpennington » Mon Jul 07, 2014 10:15 pm

Second place at the gravity support race was Tim Miller running an inline Landshark. Tim car featured:

Chassis-inline Landshark with a lowered rear bracket to bring motor flush with bottom
Motor-production 6 ohm with polymer magnets
Gearing- 7th pinion M car, 18th Host crown. Roll out of .44 inches per turn of the motor
Body-BSRT Peugeot sharply painted by Terry Flynn
Lap total 91
Fast lap time of 7.040
Best median lap segment of 7.293 seconds

Tim's drive was consistent, had few fall offs, and brought out the car's potential
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Re: Gravity class insights

Postby jpennington » Tue Jul 08, 2014 10:36 pm

Third place at the Gravity support race was Joel Pennington with a lap total of 90, a fast lap of 6.823, and a median best of 7.290 seconds. Joel's car was:

Chassis - custom sidewinder with a Z-rail
Motor - 100 turn 39 wire with rare earth magnets in an M can
Gears - 7th m car with Host 23th
Body - Host prototype body for the mini motor chassis

Joel drove fast lap and fast median lap for the top four, but was simply out too much for an effective total. The Z rail design was develop in modern retro 1/24 scale racing and was adapted to this sidewinder. It creates more torsion and beam flex that is a desirable characteristic on some tracks.
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Re: Gravity class insights

Postby bbr » Wed Jul 09, 2014 7:40 pm

Joel,
your "z" rail car, can you hammer the car off the turns or do you have to be gentle?

Mike
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Re: Gravity class insights

Postby jpennington » Wed Jul 09, 2014 9:51 pm

Mike,
The Z rail drives with a more power on in the corners style. On some tracks it can get too much traction and tend to understeer. At the Nats we had a duster environment and I opted for it's extra traction characteristic. The sidewinder picture earlier with the tungsten weights went .2 second faster in practice than the Z rail, but I did not trust it for conditions in the building. Moral to the story is choice in the race box is good. The AFXs are the cars that are most impervious cars to track conditions (22 gram tanks with gyro motors) and placed first, fourth and fifth at the Nats, perhaps a sign of track conditions. Like NASCAR we chase conditions!
Joel
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