[astro]

First off - I am a mag racer, this is not a thread on whether mags are good or not, but on tuning mag cars. (My general aims are to make my cars handle well, without too much speed compromise - not to make cars that never come off)

I have been experimenting with adding weights to mag cars. First was with scaley bar mag cars, I had been using a button mag to keep the guide & nose down, but tried using weight instead. This seemed good, and better handling than no weight when entering races allowing only 1 magnet.

Next - my previous strategy for poor cornering handling was wider, lower mags, maybe changing the placement. Having a big pack of weights left over from the first experiments meant trying other things to add grip, reduce tipping, lower c of g and so on, basically applying non-mag ballast theory to a mag car.

So far the results have been encouraging. Sometimes the cars need a better motor, but the same is true if I had increased magnetic strength. The cars generally are a bit more recoverable on corners than cars with just magnets, but i have not been very scientific with these experiments.

So: do any of you guys use weights AND magnets? Am i barking up the wrong tree? If you do mix 'em, any tips?

cheers

Dave

 

[Scott]

I have enough trouble with adding a blob of Blu Tac and spotting a difference!

Generally speaking adding weight should only give the magnet more work to do (more weight to pin down in corners). It might be that adding weight is actually "detuning" the magnets to a more acceptable level.

Then again, most things shouldn't be mixed: beer & spirits, friendship & politics, men & women - mixtures are usually destructive.

Scott

p.s. If magnets had thoughts would they look down on weights as less able metals?

 

[Fergy]

Astro, weight and magnets work their magic in very different ways. Experiment to your heart's content. You may well find that a bit of weight can act as a "fine tuning" mechanism for magnets. There is no hard and fast rule though. Every car will react differently. Be patient and try different things. Adding weight will generally "soften" the mag effect (as Scott alluded to), and this can be beneficial on some cars where the mags let go too abruptly or the car has no "feel". The weight can also contribute to generally improved handling and/or allow you to achieve better chassis balance.

Bottom line? Yes... if the motor can cope then weight can work with magnets.

 

[GRAH1]

As fergy says the mix and match thing can help .
My ferrari 333 has often been acused of being twin mag but it isnt .It just has a little ballast behind the guide to stop the front lifting ,The single standard scx mag effecively glues the back down and the fox motor gives enough power to drag the thing round .The result is a totaly well balanced car which can turn in fast lap after fast lap with out much effort and balistic laps when I try.

 

[Guest]

Hi,

As a friend of mine says, the lighter the better. He usually takes this to extreams and doesnt run any weight in his no magnet cars, although they do go quickly!

Baz

 

[Russell Sheldon]

I don't profess to be a specialist with "magnet traction" chassis -- in fact all my attempts at building cars for this class have been abysmal -- but I would tend to agree that "lighter is better". Let the magnets do all the work!

In the Marconi Foundation for Kids Charity proxy event, there is a class for "extreme" magnet traction cars. Larry Geddes built this superb chassis, which ran very successfully:-

Since the magnets provide the traction, Larry positioned the motor up front, in order to move the physical weight closer to the guide.

This is Larry's explanation of his chassis design:-

"My current thinking behind magnet cars goes like this: the main objective is to keep the magnet(s) over the rails for as long as possible. If the magnets lose the rails a little, fishtail results, costing speed. If the magnets lose the rails completely, it's a deslot (all of a sudden, too).

The front motor design with wall-to-wall magnets across the rear solves these problems, I feel. The rear can slide a little & there will still be a magnet over the rails. And with as little mass as possible in the rear, the polar moment of the rear with respect to the guide pivot is reduced. This helps give the rear less tendency to slide out in the first place. I also tried to keep the overall weight low, because the heavier the car, the greater the centrifugal force generated, which aggrivates fishtail.

The main rails are 1/16" piano wire for stiffness. The side "pans" of PC board are just there to back up the body & mount the lead wires. I narrowed a portion of them because I didn't want the chassis TOO stiff. I used PC board because it's light & strong enough for the intended purpose. The gears are 11/33 & the car weighs 75 grams. I was hoping it would be lighter, but I didn't want to lose too much strength. The PC board is just to back up the body sides & anchor the lead wires.

One thing I think is important in these super-magnet cars is to reduce bearing friction as much as possible. I feel that the tremendous downforce would really be pressing the bushings down on the axles. Maintaining an oil film would be difficult or even impossible, & friction would be higher than desired. Because of this, I decided to use ball bearings on all four corners of the car (The front tires are fully functional, actually supporting the front end. This car is not a "tripod"). And since the pinion bearing is an "extra" (something you would not normally have in a sidewinder), I used a ball bearing there too. There is a lot of side loading on this bearing & again I wanted to minimize friction."

Kind regards

Russell

 

[astro]

Thanks for all the advice everyone! Russel, thanks for the pic of that impressive chassis, and for Larry's words on mag theory, which make a lot of sense.

Will ponder!

Cheers

Dave

 

[Tropi]

That's a superb set up by Larry - his work is always exemplary and a pleasure to behold!

The theory of reducing polar moment at the rear is spot on.
At this level of down force, I am quite certain that the ball races are a real advantage.
It then occurs to me that if the Vanquish differential were tough enough (highly unlikely I know!), then it might actually be useful with the back wheels pretty well nailed to the track like this. Similarly, with quite a lot of down force at the front (looks like at least as much as most cars have in total!) and the wheels actually bearing that downforce, even steering MIGHT be beneficial.
Interesting points to ponder . . .

 

[a Bill]

OK, this is going a bit off topic but I have to ask...

Why are the wires from the braid going to the chassis instead of directly to the motor?

I'll never be able to make a chassis that looks that good but it sure is nice to have something to shoot for

Oh, and back on topic, I happen to agree with the statement, let the magnets do the work.

 

[GRAH1]

QUOTE Why are the wires from the braid going to the chassis instead of directly to the motor?

The way Larry has arranged his wires gives the guie a self centering action with out the need for springs ,he has also been able to use a heavy guage wire to the motor with out fear of the guide binding.
I would find it intresting if Larry would send the car over to the uk for us to run at slot tech as a proxy entry for the mach 1 challenge ,Russell has sent one over to me which is absolutly superb which I will shortly be posting pics of .
Russells design is an angle winder with 2 button mags behind the guide and 2 adjustable bar mags in front of the motor .The set up looks very promising indeed.
there also is a space under the rear axle to accept another smaller mag so it gives me plenty of options when setting up.
As a rule of thumb I set the car up to run with out mags as light as possible then I add the rear mag for traction ,next I add a spot of weight behind the guide if we are looking at a 1 mag car,
One of the kids at slot tech was running a 5 mag porshe last week with a 35k red can ,while it was putting down some very quick laps it could still not live with my 1mag tsrf set up as above and still on wrexham gearing.
Getting a quick magnet car is down to finding the right ballance between horsepower and down force or youll just end up with a rocket which launches its self unpredictably into the scenery then the mags let go,(Chris Clarke take note)

 

[Race-Jan]

At our club we mainly race 32nd scale RTR plastic chassis, 1 magnet allowed (but rather restricted, max 45 mm from leading shoe, and max 50 gram strength on our scale). Minimum weight of the car with a NC-2 in it is 100 grams, so weight should be added... also in LM cars lights are allowed/required, which leads up to the following typical race setup :

http://groups.msn.com/hobbyfoto/slotracepr...oto&PhotoID=440

Note that the brass contacts also provide a suspended body float for a real smooth ride

Oh, as ball bearings are allowed, I slapped some in this car, the difference is impressive...

for the light junkies

: front are 3 and 5 mm LED on each side, rear are twin 1,8 mm leds... cap = 0,22 F and resistors to match...

the car really runs smooth, and with a total of 110 grams is rather heavy, but well balanced...

Back to topic, a setup with both mag and weight can give you a really nice handling car

just what you prefer... YMMV

 

[taxi]

I'm just a home racer with a Scalextric sport track. I've been playing around with a mix of weight and mags for a couple of months.
Some cars really seem to benefit from a bit of weight added at the front (a couple of grams of blu-tack made a huge difference to my Fly and TeamSlot Lolas). Using mags at the front is ok, but I had problems on tight radius curves where the mag moved away from the rails and - instant de-slot.
When I started to pay more attention to the front of my cars I was amazed at how many were not sitting fully on the guide, but were resting on the front wheels instead. By enlarging the front axle slots to allow the axle a bit more vertical travel cured some of my de-slotting problems without having to add weight or mags! So it's worth taking a good look at how your car sits on the track before doing anything else. (Old advice I know, but I READ it many times before I DID it!) Using something like Blu-Tack is easy 'cos you can mould it into any available space, lead needs more room.

Rob

 

[a Bill]

Thank you Graham.

 

[Larry Geddes]

Greetings All!

First I'd like to thank Russell Sheldon for posting the pics of my Marconi "Psycho Magnet Class" car. And I also thank those who expressed an interest in it, & their kind comments. I'm glad I was able to contribute something to the slot world that many find interesting, including the so-called "Geddes joint". BTW, nice job EM! I suspected the joint would draw less power away from the motor, but had not thought to measure this electrically (duh!)
The car would undoubtedly have done better if it had had either a bit more horsepower, or a bit less magnet. I don't think the usual power-to-weight thinking applies to "supermag" cars; it seems to me to be power-to-downforce, although the less weight the better, for centrifugal reasons. So I guess I wouldn't mix magnets & weights, but rather try adjusting the air gap between the magnet & track rails to fine-tune things.
Another point I feel is important is to keep the front tires on the track & actually holding up the car. The large magnetic downforce would create tremendous drag on the braid if the car were a "tripod". I tried it both ways when I built the car, & could feel the difference on the setup block (a piece of Carrera track) as the chassis was pushed forward by hand. I am a big fan of "4-wheelers", & my last 3 Marconi cars (2 non-magnet, 1 mag) have all had no weight on the braid (other than a few grams of natural springiness in the braid itself).

 

[Russell Sheldon]

Thanks for posting Larry -- and welcome to SlotForum!

Larry makes some interesting points. It's clear that conventional wisdom doesn't apply in setting-up a magnet-traction chassis. Getting the right amount of 'downforce' vs 'horsepower' is where there are gains to be made.

Kind regards

Russell

 

[Tropi]

I don't know how I managed to miss this for a whole week - that's terrible!
Larry, a BIG welcome to SF - now we have both the well-known Larries visiting here and this can only be to the forum's benefit. We hope to see more of you both whenver you can make it. It is just great to have this trans-Atlantic cross pollination and long may it continue.