Jump to content
Sign in to follow this  
MrFlippant

Magnetic Downforce Scale Apparatus

Recommended Posts

Magnetic Downforce Scale Apparatus

Inspired by several similar devices made by others using other materials (wood, metal, etc), and attempting to simplify and democratize the design and construction of a basic device to compare magnetic downforce between multiple cars, I've designed this model and provided the Fusion 360 file for quick and easy manipulation to accommodate different types of rails (from track as shown, or just bar steel if you want) as well as different scales. By just changing the parameters in the Fusion 360 file, this design can be easily adjusted for any combination of those things, and then printed out and put to use in a single day of printing.

The files are free to download at the link below, which also includes additional detail on design and construction. If you already have a Magnet Marshal, then you certainly don't need this. But if you've wanted one without spending nearly so much, this might be for you.

https://www.printables.com/model/280855-magnetic-downforce-scale-apparatus
 

Share this post


Link to post
Share on other sites

Hi Greg interesting having come up against this problem in a recent proxy series , how accurate are these as going by the Magnet Marshall Sports Racer used  the same motor set up in 3 cars basically the same showed 3 differing reults not by a little but a lot again according to Paul from 30 odd gs to 80 odd the latter figure i found very hard to beleive , as people i spoke to had never heard of that higher figure in a 23k S can so how accurate are things like Magnet Marshall's.

  • Upvote 1

Share this post


Link to post
Share on other sites

I'd be interested to know more about the cars and device that was showing such wide ranging figures.

That said, I've found the official Magnet Marshal to be quite accurate, even between units. I never did any tuning to my MM, but it reads the same amounts within a single gram as the one the club uses.

The printed one, not so much. Too many variables for one scale to match the readings of another scale, not the least being the accuracy of the printer that the parts are printed on. To assist in consistency, it's probably a good idea to use some kind of tape or glue to mount the scale to the base, and then the plate to the scale. Blue/painter's tape on both surfaces to bind, and a few drops of CA to hold the tape together should do the trick nicely without permanency. Or those 3M "Command" strips that are easily removed. This way, the scale will remain centered on the base, the plate centered on the scale, and the plate not able to rock or tilt during the measuring process. Even then, though, the scale should not be expected to match other scales. 

This is for people who want to do some comparisons between their magnet cars without dropping $250 on a Magnet Marshal 2.

 

Share this post


Link to post
Share on other sites

Greg i am interested in this after our 3 cars were penalised a lot in the touring car proxy run by Paul if you look at the thread on here on the 21st October 2021  in the practise race you will see Paul stated our 3 BRM 23K motors were all differant 111topped out at 75 , 90 same motor at 52 and Johnnie E at 32 , i have been thinking of actually getting a magnet marshall to use here but the cost is to much the way things are .

Cannot tell you what magnet marshall Paul used as i only know of one hence my asking for your input don't want to have this problem again in future builds , one thing we were not aware of here was a number of tracks used magnabraid , all 3 cars were set up here on copper tape tracks , as you would know no effect at all on track mag pull

  • Like 1

Share this post


Link to post
Share on other sites

well... do you have a set of taps to put your own thread in some steel bar? If so, or you want to buy taps, then I could do the version I thought of that uses a trapped bolt through threads in each end of the steel bar. The point is to allow you do raise/lower the steel bar to adjust how much pull it exerts. This might allow one to dial the 3d printed scale to be fairly close to the device being used elsewhere. You'd kind of need them side by side to test and tweak and test and tweak, though. Otherwise, there's no guarantee that your scale will be anywhere near their scale.

Edited by MrFlippant

Share this post


Link to post
Share on other sites

This might sound a bit silly Greg so what i'm understanding a lot of this rests on the hight of the motor in the car relative to the track , and by what your saying these mag marshalls are not all the same as regards the measurements , so i can make my own giving me a certain reading send it to the proxy where his magnet marshall reads differantly to mine so we end up with the same argument as to who's is right

I have all the parts i think i need to make one of these so worth having a go thanks for all the advice.

Share this post


Link to post
Share on other sites
Quote

 

This might sound a bit silly Greg so what i'm understanding a lot of this rests on the hight of the motor in the car relative to the track

Yes that is correct

The Magnet Marshalls are all set up the same at the factory (I guess) but do vary a bit

all the MM dose is measure in grams the force that the magnets from the motor  and or the traction magnets apply to the tyres

A pictures worth a 1000 words ( in my case 100 000) words

 

  • Like 1

Share this post


Link to post
Share on other sites

Interesting sticks thanks for the video info , he must have been using a car with the magnets still in chassis situ to get that reading , think my suggestion of a one type series motor wise to Sports Racer might solve any future problems as all the motors should be round about the same mag pull, hmm i wonder about that

Share this post


Link to post
Share on other sites

yes, even with the much more precise Magnet Marshal 2 product, there's no guarantee that the numbers will match to the gram unless it can be adjusted and compared with the "official" scale to ensure parity. That's why one of the major improvements to it was the ability to adjust the bar in order to get two machines to be closer in their measurements. 

At this point, I think I'm going to go ahead and move forward with my idea for an adjustable one. The down side is that, unless I can find a piece of metal with threaded holes at each end, people will need to buy the appropriate tapping tool as well as the metal, a hacksaw, and other tools that they may not have on hand.

Edited by MrFlippant

Share this post


Link to post
Share on other sites

Not only is the airgap between the motor and track going to affect the reading but magnetic field strength isn't a linear relationship, it's exponential.

If you raise the motor 0.1mm and measure the mag effect, then lower the motor 0.1mm the change in magnetic effect readings aren't going to be equal, the nearer the motor is to the track the faster the magnetic effect rises.

So the same motor in two different cars can give you wildly different readings.


Life is like a box of Slot cars...B)

Share this post


Link to post
Share on other sites

Of course. That is physics. What you say applies to all such devices, whether expensive manufactured scales, or cheap DIY ones.

All of those things will effect the reading the car gets on the scale (any scale) as well as on a track that has ferrous rails.

Those things explain why two scales will have different readings of the same car, even scales that are manufactured in the exact same way (e.g. two Magnet Marshals).

That's also why the Magnet Marshal 2 added the ability to easily tweak the position of the steel bar, so that it can be made to be closer (don't expect a perfect match) to another scale, so that both scales can be useful to club members, such as a "club" scale and someone's personal scale.

And... why I'm going to be designing an adjustable version of the 3DP scale. If anyone has leads on steel bar of a suitable size to act as rail, with pre-tapped holes at each end, I'm all ears. :)

Adjustable or not, the device is still useful as a tool of comparison, regardless of the actual number shown on the scale.

Share this post


Link to post
Share on other sites

I updated my design to include a way to adjust the height of the rails in order to "calibrate" to another scale. The models provided are for Scalextric Sport track rails and a 30mm tall scale. If you have a scale of a different height and/or want to use different rails, you can edit the parameters in the included Fusion 360 file, or PM me to adjust the models for you.

https://www.printables.com/model/286374-magnetic-downforce-scale-apparatus-adjustable

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...