Magnet-less Racing: Adding weight

[jfuente]

Greetings HRW,

I'm wanting to venture forth into magnet-less racing. I'm guessing adding some weight to compensate the removal of the magnet would assist in cornering. I'm not trying to replicate magnet racing, but have heard so much talk about balancing a chassis in advanced tuning. I'm intrigued by SCC's chassis balancing tool and have read a lot of people using the 40/60 as a good starting point.

• I'll be racing on Policar 1/32 plastic track
• What's a good starting weight, 1:1 for the weight of the magnet or possibly 2:1 ratio?
• Also, what's the preferred weight? I've got kids, but figure the weight is inside the chassis so the chance of lead poisoning is significantly diminished.

Cheers! Enjoying the adjustable Policar powerbase, trying to find that sweet spot but wouldn't mind bumping it up a bit by adding some weight after removing the magnets.

[RichD]

There are few hard and fast rules for adding weight to cars for non-magnet racing. Most clubs probably reduce the track voltage when they chuck the magnets, SMR runs at 10 volts. For a start you should at least add a small weight just behind the front axle to keep the car from doing wheelies when full power is suddenly applied. Besides adding grip magnets effectively lower the center of gravity of a car. If it is legal to do so you can remove the stock interior and replace it with a vacuum formed one to decrease the top weight. Any weight that you might add should be as low in the car as possible to lower the center of gravity and keep the car from wanting to tip in the corners. Added weight should be just ahead of and behind the motor. If the car has enough ground clearance you could put very thin lead sheet on the bottom of the car, providing that it is legal to do that. You will need to experiment to determine how much weight will be needed, often two different examples of the same car will need different amounts.

[Bal r 14]

When I switched from Scalextric plastic track and cars to a routed MDF track I found the cars were faster and bounced around a lot, because the wheels/tires were not true. I also found the amount of contact the front wheels have with the track is a huge factor in how they handle and how much weight is needed. If they touch too much, they have a negative impact on steering. If they don't touch at all, the car can roll over easier in a corner, kind of like a tricycle. I set the front tires so they just touch the track. In many cars, you can't adjust the front wheel setting. The way to do is reduce the diameter of the tire. The point of this post is:
1. Get yourself a tire trueing machine. You are going to need it.
2. Trueing tires and setting wheel height will have a lot of bearing on how much weight you need and where.

[jfuente]

waaytoomuchintothis can you expand upon the use of "hard as nails" on the front tires? Is it to add back diameter or to slicken them up to reduce drag on the track? Already got my tire razor on order from Jon.

[waaytoomuchintothis]

"Hard as Nails" is a product women use to harden their fingernails. Its in your grocery store or drug store. It makes a perfect glue for tires to wheels, and will let go when you want to pull tires off. It is particularly effective on rear wheels. It may surprise you how much wheels can spin inside the tires on takeoff, and what a difference it makes to have the wheels stuck to the inside of the tires. I don't like front tires with junk on them to make them slip on the track. The same goes for the fronts being off the track so much that they spin after the car stops, the so-called tripod effect.

[jfuente]

Gotcha! Thanks! I'll pick some up.

[Kevan]

Glued&trued all round and all 4 rolling on the track, set guide height low enough so the fronts still roll...tyres are king where lap time is concerned.
I prefer ballast out wide and between the front & rear wheels plus sometimes between the front wheels but always as low as possible and always below the axle line.
I weigh my cars and aim for 90-95g for a large car like a Mosler.
After that it's motor and gearing, I rarely venture above 22k and always start at 2.6-2.8:1 for cars with what I'd call normal size wheels and tyres. Historic cars with large wheels and tyres need a larger spur/crown and/or smaller pinion to get the same rollout as cars with 'normal wheels and tyres' so the motor is doing the same work with a similar speed/acceleration/braking characteristics.

[mattb]

I don't run the same type of cars as you guys, but on my 1/24 cars, I like the front wheels to turn when the car is setting still. Might drag the track a little but they will turn. Seems to put most weight on the guide, but the wheels contact enough to not let the chassis roll in a corner.

Lot of guys on here throw away magnets and convert to traditional slot car racing. You ask these guys about a particular car and they will know what works best for their track and that will give you a good starting point.

[Billy boy]

keep the magnets for chassis straightening and holding things to the fridgeyou know,usefull things

[Kevan]

Mag racers use them...if they didn't they'd be magless racers.

[Pappy]

Billy boy, I don't even worry about the chassis being straight. I found out that if you have an adjustable front axle and the front tires are both barely touching the track it works just as good as a straightened chassis. 
I went to the Michigan 24 with three Daytona Prototype chassis that had been straightened in hot water in the oven and all three of them broke during test and tune the day before the race. It made the plastic brittle. I'll never straighten another one.

[chrisguyw]

Adding weight can significantly improve the handling/lap times of your cars, but it should be considered a final "fine tuning" element, not a bandaid to mask other issues with the car...eg,....if your car has out of true wheels/tires (both front and rear) no amount of weight will cure the problem....so

1/ Build the car to the best of your ability........round tires, aligned/glued bushings, motor secured, guide height set, appropriate gear ratio, flat chassis, front tire vertical position adjusted/set, some body movement on the chassis, and then,...put in on the track, and the car's performance will indicate where and how much weight is needed.

2/ Several factors will come into play when deciding how much and where.......these will include, how well you executed the initial set up, as well as tire grip, motor strength, track grip and the general layout of the track (is it tight twisty, or fast flowing ??)

While I am not trying to avoid your question, I really cannot give you a definitive answer...........there are (as indicated above) a multitude of variables, so you really must experiment.

A few basic fundamentals.........If the car comes out at the nose, or tips out, generally weight at the front will help, weight placed lower in the chassis will lower the cg, and help the car to slide rather than tip, weight placed higher in the car (above the axle centerline) will raise the cg. and can help with grip. (this will likely not be the case in many of the cars you are running).

Less weight placed on the perimeter of the chassis will be generally have the same effect as more weight placed inboard.

While most competitive cars do end up around the 60/40 split (60 rear), but, do not get hung up on this figure..........try your unweighted car first, and go from there.....let the lap times dictate the weight balance.

Use a couple of grams at a time,.....bearing in mind that all things being equal, a lighter car does have some fundamental advantages over a heavier one. If adding weight in one area does not help, do not add more in another area just to compensate.......remove the weight that did not improve things and try a different position,...the best balance/lowest lap times are the obvious goal, using the least amount of weight possible.

At our local area clubs' (12 tracks) we run over a dozen varied classes, and car weights vary (depending on the class) from 60gms to 95gms, so , again weight will vary with motor/tires etc. etc.

As far as what to use,...most slot shops sell adhesive backed lead sheet, which if placed inside the car (most clubs mandate this) should be safe for the kids......if you are worried, bits of brass/steel even modelling clay/putty can be used.

Hope this helps, and let us know how you make out.

Cheers
Chris Walker

[HO RacePro]

You want just enough weight in the front to keep the guide slotted under acceleration.

When adding weight it helps if the weight is able to freely pop up and down. This absorbs shocks to the chassis. It really does help.

Ed Bianchi

[Pappy]

When making adjustments to your car or adding weight, do one thing at a time and test it. If you do two things they may cancel each other out. One thing might improve the car and the other might slow it down, you'll never know if either one helped.

[waaytoomuchintothis]

Once again, Pappy is right. Use good science, adjust one factor at a time, and you'll be proud of what you get. In my experience, learned from the early TransAm Mustangs and Camaros, a good goal for total weight is around 65-70 grams. You can come far short of that goal and have a very fast car without getting stupid fast and ruining the experience. Also, don't forget to make the connection from body to chassis as loose as possible. What a difference that makes!

[jfuente]

Wow! Appreciate the sage advice. Adding a tire razor to my list of things to pickup.

Thanks gents!

Edit: Currently emailing Jon to get a tire razor.

Also, once the wheels and tires are trued, for cars like these policar BRZs, with snap in non-adjustable front axles, how do I adjust the front ride height? Spacers on the guide?

[chrisguyw]

A few options,(one or all combined) depending on how much adjustment is required ..... guide spacers, thicker or thinner braid, and careful sizing (diameter) of the front wheels/tires.

PS If you are looking at tire truers, you may need to look at a power supply to run it...........which can also double as a power supply for your track, which makes the purchase a bit more attractive.

[jfuente]

Hoping I can just run it off a 2 or 3 cell lithium polymer battery I've got for RCs.

[Kevan]

2S or 3S lipo are too high, 4v is ample. If you have a lipo charger it may have a volt-out option, I use an old LRP Pulsar charger with this option, you'll really need to see the amp draw so you know how hard the grinder is working, I like to see no more than 4A or the tyres will overheat.

[jfuente]

Got a 0-30 V / 0-10 A variable power supply on order. Thanks!

[RichD]

Here is an article on tuning a car for non-magnet racing: https://drive.google.com/file/d/1qBi...ew?usp=sharing

[jfuente]

Bookmarked!

[jfuente]

Tire razor is ordered up with a wheel buddy.

[jfuente]

Direct from Jon -- https://www.homeracingworld.us/PitRo...zorsupport.htm

[oldskool62]

Unfortunately no go direct.

[jfuente]

Direct via his email? I just got mine last week from him. E-mail should be scrjon160 at aol dot com