Matching magnets

[ChallengerGuy]

After reading an ebay auction, I trudged over to Harbor Freight and picked up a "US Balance" US-Magnum-1000XR professional precision pocket scale for $10.99 plus tax.

The nice thing about this scale is it comes with a removeable plastic cover and a metal plate used as it weighing platform. Like the ebay auction item I saw, I drilled a 5/8ths hole into the plastic cover directly over the circular control panel. I am now able to operate the scale without removing the cover.

I then press the on button, wait for it to zero, then I place a t-jet magnet on the plastic cover and read the negative gram reading. My values range from the low 4s/high 3s all the way up to 14grams with most of the red and white magnets falling into the 7,8 or 9 gram range. I have made a small plastic container to group my magnets and look for balanced pairs (or to locate stronger rear magnets to facilitate braking).

Feel free to lend your thoughts on this methodolgy. For $10.99 it was the simplest solution I could find and the scale also doubles as a "scale" to weigh my cars.

Good luck!

[dge467]

That's a pretty cool idea. I might have to pick one up.

[TeamMadMarsupial]

Built one of these a few years ago. It works great! I attached a small piece of steel to the scale using double sided tape. As mentioned, it works great for matching magnets. I also use it to measure "magnetic downforce" on all my cars. Just place the built car on the scale and move it around to find the sweet spot, where you get the highest reading. On cars where our club allows adding weight, this method also shows how much one car differs from another with different magnet and weight combinations.

This works great on Magna-Traction cars and I can even get good readings on the T-Jets and AFX Non-Mags where I have installed a set of high strength polymers.

The only thing I have not figured out yet is how to measure the difference from the front axle to the back. Would like to do this to work on balancing the downforce and R&D to find what front to back % works best from class to class.

[RichD]

I amj not sure what you are getting at when you speak of front to back axle. Normally you would want both magnets to be the same strength because the motor works best that way. If there is a big mismatch the armature gets dragged to one side and that wastes energy. You seem to want to study the effect of shifting the magnetic downforce to affect handling. In that case just knowing how strong the magnets are may be all you need to know. No mater what measurments you take at the end of the day you have to put the car on the track and see what your lap times are. That is the reason why I don't have a dynomometer. With 1/32nd motors I just use a non-contact tachometer to be sure that the motor is half way decent, then put it in the car to see what it does on the track.
You should be aware that opposite ends of these magnets are usually not the same strength. Some people measure the ends and place the stronger ends so that they are facing in the direction that the armature poles will be coming from. That means installing some magnets upside down.

[TeamMadMarsupial]

Not looking to use different strength magnets. More to looking at where my cars like to be as far as total front to rear weight percentage with a measurable number. I have some cars that seem to skate the front end (what would be considered a push on a full size car). I have others that get loose with too much front weight. So, just thinking it would be neat to see the balance front to back and where the measureable sweet spot would be.

I am always tweaking my AFX Non-Mag cars to get a perfect balance. These cars can be a hand full with an arm around 2.3 to 3 ohms. The weight helps plant the car and eliminate wheel spin. Since we don't have any rules regarding weight, I use whatever I can to increase the tractive effort with weight, similar to the idealogy used to get steam engines to utilize their power instead of just slipping on the rails.

Some guys I run with mess with diferent strength magnets, front to back. It seems to work for them, but I always understood the use of matched magnets to be the goal, as you confirm.

[Slot Demon]

AFX non mag chassis is what HOCOC and most of the other clubs around New England base the coupes class on . We call Rich Dr. Speed.... His cars especially his coupes are hard to beat....alway's very fast.
Trent