# Magnetic Downforce Tester



## vaBcHRog

Hi everyone,

I read about this a while back and bought one. Its a scale called US-Magnum 100XR. Here is a link to buy one 
http://www.amazon.com/US-Balance-US-MAGNUM-1000XR-Digital-Jewelry/dp/B0016PF0SUw

It has a steel plate and plastic top. You drill a hole for the guide pin and a hole over the reset power button then use a tooth pick to turn it on and off.



















You place the chassis on the plastic cover and the magnetic pull of the chassis pulls up on the scale and you get a negative reading. Real long guide pins have to be removed or it will push the scale down. Most skinny wheeled TJETS read between .8 and 1.1 with stock magnets. 










A JL Tuff-one reads . . . 










An AFX reads . . . 










An AFX MagnaTraction reads . . . 










An Autoworld XT reads . . .


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## wheelszk

Link does not work.


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## vaBcHRog

Try this one

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200403824185


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## Hilltop Raceway

The guys on the other networks use the scale to measure motor magnet strength also. Mark a spot on the plastic case, then place your magnet on the same spot everytime. You'll get a negative readout, (I believe I'm correct), but you can judge the magnet strength by the reading. Find the magnets that give you the best reading and match em up. Just a poor man's testor...RM


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## wheelszk

vaBcHRog said:


> Try this one
> 
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200403824185




Thank you. :thumbsup:


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## SwamperGene

That's pretty cool.

If you already have a plastic-bed pocket scale, you can make a downforce scale pretty easily with some legos and a hunk of steel long enough to straddle the scale. 

:thumbsup:


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## Voxxer

*Tester*

Hi:

You can pick them up at Harbor Tool and Freight, however, most stores do not have them on the shelves. It seems that " drug dealers " use them to weigh certain stuff. At the store close to me, the have them under the registers and you have to ask for them by name. Most of the time they have them for $10.99 each.

www.voxxer.com

Voxxer


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## eastside johnny

Roger, From your pictures it looks like you are putting the cars on the plastic with tires & on the cars. Can you see a difference in the readings with various tire sizes? The hole for the guide pin will locate all your cars/chassis consistently but I would think to compare various cars/chassis it would be good to have the chassis "bottomed out" on the plastic to first eliminate the variable of tire size. Just curious how extensive you are using it. Looks like a great way to set up & judge magnet cars for sure. Thanks for sharing with all of us.


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## vaBcHRog

*More Testing*

Here is a VHORS car with slipons and stock magnets










Same chassis with JL magnets










Same chassis Dash Magnets










Same chassis Super II magnets










G JET










I put the VHORS chassis on the skid pad I'll write this up later


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## LeeRoy98

Thanks Roger, I got mine yesterday and drilled to mirror your setup. Works perfectly!! Some very interesting data!

Thanks again for the tip,
Gary
AKA LeeRoy98
www.marioncountyraceway.com


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## Patom

Got mine. holes are drilled. Let the fiddling begin!
Thanks,
Tom


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## T-jetjim

What a great idea Roger. I like the idea of using it as a magnet meter. I can't afford a Gauss Meter so I tried to do the BB's in little baggies for the magnet matcher. Way too many variables to be consistent. To top it off, the first magnet I did was super strong and I based all of the other baggies off of it, counting out the BB's. Then I tried another magnet and it couldn't lift 1/3 of the first one. I spent the next hour recounting BB's only to determine that this was not a very consistent process.
I'll have to try this.
Jim


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## neorules

Guys-- I posted this info about the scale last year on some boards. I found the scale at Harbour freight bought it and saw the negative reading when I set a car on the plastic cover. That got the wheels rolling regarding using it as an easy magnet tester. I test cars without tires to get the potential, then can set up with different tires to suit the track. I have found another device that tests the break away force of a car. The value of this is for advanced unlimited car building as well as easily getting a car that works on one set of rails set up for another.


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## ParkRNDL

Is this thing sensitive enough to measure strength of individual Tjet magnets? I'm getting my credit card fired up as we speak...

--rick


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## Voxxer

*Tester*

Hi:

Here is what I do with that magnet tester.

Test you car as in the pictures, note the number!!!!!!

Then, WITH THE COVER ON, draw a cross at the center of the silver plate. Measure out from the center horizontial line the distance for a magnet, half way from vertical. Now you have a point that will always read the same for each magnet. Place the magnet on the point in a convex manner, the two ends down on the plastic and the top curve over the cross. Use a fine point shapie to write the results on the magnet. Measure all the magnets. Match up all sets. Here is the cool part. With each set, just like it makes a circle, place it centered in the cross. You will have a reading. Now, turn the magents over, note the reading. Finally, switch one of the magnets, paint side down for one, note the reading and then switch the other paint side down, note the reading. You will have found the highest down force for the set of magnets. Place them in the chassis( as the you have found the highest reading ) with the tires and see the results.

This also help with the arm, since the down force in heading towards the bottom of the chassis, it will " pull " the arm down on the brushes making a better contact.

www.voxxer.com

Voxxer


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## NTxSlotCars

So, what are the limits of the scale? I mean, can you test them high dollar neo cars?


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## AfxToo

Here is a good source of weigh scales in all kinds of different form factors, some of which are probably catering to the shady side of weighing things, but the products are good. I'm sure you could use some of the smaller ones to do a 4-point downforce tester for setting up a car.

http://www.americanweigh.com/

I'm a bit leery of using the negative reading method only because I don't know where the calibration is zeroed with respect to the full range of the measuring device. In other words, if the scale is designed to measure 0 to 100 grams can it also go from 0 to -100 and is it linear in the negative direction? You don't really know. But there is no doubt that this is a very handy little method for obtaining quick & dirty relative measurements of the magnetic influence of a particular setup.

It would be interesting to looking at doing some sort of a plunger or "bed of nails" type configuration to achieve a positive downforce profile at several points with the 4 tires being the most interesting ones of course. 

I'm very intrigued by the potential of these little scales...


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## LDThomas

Most of the other scales out there do not have steel (magnetic) platens so your choices are rather limited for this specific application. As to the negative number not being linear, who cares. The only thing that matters is that it is repeatable. As such you now have a magnetic downforce and magnet strength comparator.


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## SwamperGene

AfxToo said:


> In other words, if the scale is designed to measure 0 to 100 grams can it also go from 0 to -100 and is it linear in the negative direction? You don't really know.


You _could_ put the car on, zero the scale, then remove the car for a positive reading.

:tongue:


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## AfxToo

> As to the negative number not being linear, who cares. The only thing that matters is that it is repeatable.


If anything beyond a certain strength magnet all read the same value because of the way the pressure/load sensor is constructed then I would care. That's all I was getting at. What kind of numbers are you getting with high grade neo magnets, like N42 or stronger? 

For a multipoint downforce tool (putting a load sensor under each wheel) you would not want to use scales with magnetic platens since you would be using a representative track piece with rails as the source of magnetic attraction and using the scale in the positive sense.

The scales like these that I've used don't have a zero adjustment. They use a calibrated reference weight. 

Neo - care to share your break away measuring jig with us?


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## Voxxer

*Another use*

Hi:

Another thing I do with the tester is to have two placed next to each other. I place the front of the body on one and the back on the other. I feel this help to find a " balanced body " for racing and drag racing. In drag racing, this helps find the body with the heavest front to help with the pick-up shoes, if you can't add weight.

Voxxer


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## vaBcHRog

I don't have any neo casr but do have a couple with Polys in them I'll take areadding tonight


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## neorules

The scale I have tops out at 219.1 grams. I use another method to test the neo cars. I think the level 25 cars are around 175-190 grams. We could space the cars up higher if we wanted to check relative strenght if that particular car "pegs the meter" so to speak.


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## roffutt

I've been using this scale for a few months now, I've bought a few. I almost like it better then the top-of-the-line gauss meter I own. I find its very accurate and can quickly see the difference from magnet to magnet. It's a great point of reference for matching magnets, but I can say I do not get the exact same readings from one scale to another, but scales I tried have been consistent. 

My recommendation: Instead of using grams as a unit of measurement, I use grains. There are approximately 15.5 grains in 1 gram, So, you get a more precision measurement, although I believe this scale is only accurate to within + or - 2 grains. 

Also, the top metal plate you see is not magnetic. It's just a thin piece of stainless steel glued to the steel plate below. The lower metal plate, which provides the magnetic attraction, is screwed to the load cell , the area where the plate is screwed to the load cell is recessed (left-middle of the plate), and is not a good place to measure magnets in because it provides less area for the magnet to be attracted to. (I'll add a picture when I have a chance) 

I think it's also import to make sure the plate is parallel as possible to the plastic cover, when the cover is on the scale. I had one scale where there was a slight bend in the plate, so I was getting varying readings from north to south. For this reason, it's a good idea to always be consistent on where to place the magnet to measure on the scale, always place the magnet in the same spot. 

I mostly measure match just bare magnets. I've also drilled a hole for the guide pin and measured the full chassis pull force. I've found this to be the less consistent readings, even when measuring the same car multiple times. I feel this is because of the recessed area in the plate mentioned above, and it is very difficult to place the car in the exact same spot from reading to reading. I planned to add a alignment fixture to the cover, but have yet to do so.

Ball park readings I see with my scale: (lower is stronger)

storm ceramic motors (motor face down): -260gn to -340gn
storm ceramic tractions (track side down): -350gn*
* I don't recall the exact range, I do remember them being very consistent in values.

storm poly half 19 tractions: -650gn to -760gn
storm poly full 19 tractions: -750gn to -900 gn
storm poly half 25 tractions: -790gn to -950 gn
storm poly full 25 tractions: -1020gn to -1330 gn

-Robbie


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## roffutt

AfxToo said:


> If anything beyond a certain strength magnet all read the same value because of the way the pressure/load sensor is constructed then I would care. That's all I was getting at. What kind of numbers are you getting with high grade neo magnets, like N42 or stronger?
> 
> For a multipoint downforce tool (putting a load sensor under each wheel) you would not want to use scales with magnetic platens since you would be using a representative track piece with rails as the source of magnetic attraction and using the scale in the positive sense.
> 
> The scales like these that I've used don't have a zero adjustment. They use a calibrated reference weight.
> 
> Neo - care to share your break away measuring jig with us?



Afxtoo,

I forgot to mention I've tried various strengths of nickle-plated neo magnets up to advertised as level 52, and can see the differences between a level 52 & 42 of the exact same size. 

Obviously a large, very powerful magnet could possibly saturate the scales measurement. But, I think it would be have to be a larger then what you'd currently find on a HO slot car. 

I also don't think a negative reading versus a positive reading matters, because of how the scale works. If it were more of a calibrated spring/mechanical type device I could see a valid concern. 

I also thought about a trying a 4 point chassis measurement device, but I think it very difficult to get 4 scales to be precisely placed and same exact height to get an accurate reading. There is surprisingly very little electronics in these devices, so someone with the ability to fabricate jig, it might be worth while.

For less the $10 at harbor freight, it's be fun experimenting.

-Robbie


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## AfxToo

Thanks for the data!


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## ParkRNDL

Got mine today. Very neat little gizmo, works great for comparing strengths of similar magnets... I learned there's a big variation just in white stripe/black or green/orange magnets, for example. I have a big box full of Tjet magnets of all different colors... when I took this thing out and set it up, I organized the magnets into N and S and then further subdivided them by color/markings. Now when I'm putting a car together, it's easy to grab a few N and S magnets in the colors that should designate the strength I'm looking for (Tjet, TO, AFX, etc.) and test them till I get a matched pair, then file the rest back where they were till I need another pair.

Certainly a lot more convenient and consistent to use than this:

http://www.coolmagnetman.com/magmeter.htm

I built one of these a few years ago, but I've only used it a couple of times since... it's obviously kinda cumbersome and primitive...

Thanks for the tip, Roger!

--rick

edit; by the way, Robbie, I am using your suggestion of measuring in grains. works great...


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## SwamperGene

ParkRNDL said:


> Certainly a lot more convenient and consistent to use than this:
> 
> http://www.coolmagnetman.com/magmeter.htm


Did you try mounting it all into a project box? That circuit is basically what we all know as the BRP mag matcher, which _is_ pretty convenient and consistent.


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## ParkRNDL

SwamperGene said:


> Did you try mounting it all into a project box? That circuit is basically what we all know as the BRP mag matcher, which _is_ pretty convenient and consistent.


no. mine is all on breadboard, with the wires just jammed in where they belong like in the pics on that website, and stuck into a little cardboard jewelry box. i never got good at soldering. don't get me wrong, it worked... it just felt like it was gonna fall apart every time i took it out... and i was never sure if i had the magnet in the same sopt twice. i'm sure the concept and the materials are sound, it's just that my execution leaves something to be desired...  :lol:

--rick


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## SwamperGene

ParkRNDL said:


> no. mine is all on breadboard, with the wires just jammed in where they belong like in the pics on that website, and stuck into a little cardboard jewelry box. i never got good at soldering. don't get me wrong, it worked... it just felt like it was gonna fall apart every time i took it out... and i was never sure if i had the magnet in the same sopt twice. i'm sure the concept and the materials are sound, it's just that my execution leaves something to be desired...  :lol:
> 
> --rick


lol ... did you maybe buy more than one of each of the needed parts? If you send me enough parts to make two, I'll make us each something similar.


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## Voxxer

*Tester*

Hi:

The tester is on sale for $9.99 this week. You will need the coupon.

Voxxer


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## ParkRNDL

Drat. I just paid 25 bucks plus shipping off Fleabay. I couldn't find it in the Harbor Freight online catalog.

Sigh...

--rick


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## SwamperGene

Voxxer said:


> Hi:
> 
> The tester is on sale for $9.99 this week. You will need the coupon.
> 
> Voxxer


Ours has 'em in the store for 10.99 this week, no coupon.


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## LDThomas

*Great little item...*

One more tidbit: Drill a third hole over the "MODE" button. Set the scale to "gn" rather than "g". The accuracy is over 50% better in this mode (grains) rather than in default gram mode.


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## Dyno

I dont have a Harbor Freight near me and I couldnt find it online, so I just paid more than 20 bucks...oh well. Should be here friday.


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## eastside johnny

Well.it looks as though Roger's thread here boosted their scale sales......next thing you know, there will be a bunch of black sedans parked at the end of our streets wondering what is going on!!!


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## Voxxer

*Scale*

Hi All:

Found out a little trick today. Go to www.harborfreightUSA.com not the regular web site.

Under item number type 97920 for the scale.

www.voxxer.com

voxxer


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## Montoya1

I have always suspected that if these methods were more widely used and the major orgs sorted their classes via them, that the shifting magnet market would suddenly become stable!

If the racers can set up a car for a class a number of ways independant of what the manufacturer says about what magnets will be in their chassis down the line, it gives the power to them for a change.

It certainly works in 1/32nd scale, but then again apart from slot.it and NSR the manufacturers are not guys you can phone up and be on first name terms with. Its a slightly skewed comparison therefore, but still food for thought.

I always find it predictable when the dogmatists for the ''big three'' attack the notion of teching cars this way....


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## roffutt

LDThomas said:


> One more tidbit: Drill a third hole over the "MODE" button. Set the scale to "gn" rather than "g". The accuracy is over 50% better in this mode (grains) rather than in default gram mode.


I've done this as well. But, I've found some scales I've bought actually remembers the mode setting from last use. In the 4 scales I've bought, 2 remember the setting and 2 have not. Not a big deal, just a minior inconvenience. I wish there was a way to make it stay on longer then 1 minute auto off feature. I think 4 or 5 minutes would be ideal. 

-Robbie


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## majdave79

*magnet matcher*

if you take the simple gaussmeter and mount it in a project box... add a cut down chassis to hold the hed, it will look like this:


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## majdave79

If you end up with a scale that doesn't have any steel/magnetic material in the plate, all is not lost. Using a dremel, I cut away a small section that the t-jet/car can straddle. (peek under the plate to ensure you don't cut where the plate attaches to the scale mechanism). (details for this mod on the Slot-Rev site). I then epoxied some metal down inside the scale to attract the magnets. Now the car sits on the scale and pulls down towards the metal. I am still trying to figure out a way to "calibrate" the scale... matching the downforce to the same downforce present when the car sits on the track. I'm trying to find a car that will just barely hang onto a track piece upside down, then I'm going to add metal until I can get the same car to just barely hang onto the scale. Any other ideas out there?

Dave


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## majdave79

amazon.com is cheaper


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## majdave79

*magnet checking*



Voxxer said:


> Hi:
> 
> Here is what I do with that magnet tester.
> 
> Test you car as in the pictures, note the number!!!!!!
> 
> Then, WITH THE COVER ON, draw a cross at the center of the silver plate. Measure out from the center horizontial line the distance for a magnet, half way from vertical. Now you have a point that will always read the same for each magnet. Place the magnet on the point in a convex manner, the two ends down on the plastic and the top curve over the cross. Use a fine point shapie to write the results on the magnet. Measure all the magnets. Match up all sets. Here is the cool part. With each set, just like it makes a circle, place it centered in the cross. You will have a reading. Now, turn the magents over, note the reading. Finally, switch one of the magnets, paint side down for one, note the reading and then switch the other paint side down, note the reading. You will have found the highest down force for the set of magnets. Place them in the chassis( as the you have found the highest reading ) with the tires and see the results.
> 
> This also help with the arm, since the down force in heading towards the bottom of the chassis, it will " pull " the arm down on the brushes making a better contact.
> 
> www.voxxer.com
> 
> Voxxer


Great tips! I checked a pair of very weak black/black magnets. In one direction they were significantly weaker than a pair of green/white magnets. Flipped over... as a pair... they were stronger than the same green/white magnets were in either direction. Now I just need to test them in a chassis on the dyno to see if the strength corralates to performance.

Dave


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## 440s-4ever

majdave79 said:


> I am still trying to figure out a way to "calibrate" the scale... matching the downforce to the same downforce present when the car sits on the track. I'm trying to find a car that will just barely hang onto a track piece upside down, then I'm going to add metal until I can get the same car to just barely hang onto the scale. Any other ideas out there?
> 
> Dave


Mount a piece of cut down track to the scale. Put car on scale, zero, and slowly pull til break away is achieved, you'll have to watch for max reading and should do multiples looking for a consistent number to emerge from the jumble. Technique will be a heavy factor and you may even want to rig some sort of lift mechanism that can move slower & steadier than your hand.

Good luck!


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## Joe65SkylarkGS

I got my 10 dollar scale at HF. But I haven't messed with it too much. But I have to say, it's amazing the weight difference in these t-jets!! 

I'll report my findings when I get to it!!


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