10 replies to this topic

[Paul Lindewall]

Somehow (and I have no idea how!) my track - Copperhead Motorsports Park in Boiling Springs, SC - (see how I slipped in a shameless plug there?  ) became listed on the HOPRA website. So, I started looking into the rulebook to see if/what changes would have to be made to the 'local track rules' to bring them in line with HOPRA racing classes. 
Currently, we have a 'Box Stock' class where nine Wizzard Storm hardbody cars, along with DS Electronic controllers, are provided to racers, so basically, people can show up to race with zero investment. I guess those would fall in line with the HOPRA "Spec Stock" class. We also offer a 'Spec Racer' class, similar to the HOPRA Spec Racer rules. Racers provide their own equipment for that class.
Anyway, I went looking for one of the HOPRA approved Spin Doctor ER Gauss meters. Here's what I found on their website:
Spin Doctor gauss meters are no longer being manufactured.

Oh, great. I have sent a message to HOPRA, hoping to find an alternative that would be acceptable. In the meantime, I was considering building my own with a circuit and components I saw listed on an Arduino project forum, and just using the readings from current stock chassis as a baseline for legality? 
Does anyone have any other suggestions, other than eBay for used Spin Doctor meters?

 

[mreibman]

well, I tried building a gaussmeter about 2 years ago. I had pretty much no success. Here is an excellent article on that topic: https://www.coolmagn...om/magmeter.htm

 

I ended up buying one for around $100 which was readily available.

The most common gauss/tesla meters I have seen available are similar to this one: https://www.amazon.c...0505391&sr=8-23

 

Your mileage may vary. Best of luck!

[Phil Smith]

I wonder what the guys that build them for slot car use, use for the sensor.  Hall effect sensor like in your link?

[Paul Lindewall]

Dallas Racer, on 26 May 2020 - 3:37 PM, said:

I wonder what the guys that build them for slot car use, use for the sensor.  Hall effect sensor like in your link?

 

That's what the Arduino based one uses.

[MSwiss]

Yes, they use a Hall effect sensor in the wand.

The size of the sensor, itself, and how it's inserted/installed/potted into the wand, is why one of brand of gauss meter will most likely give you a different reading than a different brand.

And the shape is why a gauss meter is really only good to compare a batch of the identical magnets, that haven't been modified.

IOW, if you shorten a magnet, it will most likely give you a higher reading, contrary to what common sense would tell someone.

[Phil Smith]

Interesting info! 

[SpeedyNH]

i once used a linear hall-effect sensor to build a magnetometer. i added an op-amp to allow zeroing the output to 0 Volts under the "no-mag" condition and to change the scale factor. i was going to build one using +/- supplies, but since the device output isn't "zero at zero", manual zeroing would still be necessary anyway so i didn't bother. (i bought several and they were each a little different.) 

i do remember running it somewhere around 7.5V(?) to get some more range out of it, though. 

 

i "calibrated" it against a lab quality unit with some test magnets and it wasn't too bad up to about half scale. 

i did file/sand down the sensor a little for weaker magnets and also made a couple slip-on spacers for it for use with cobalts & neos so i could keep it in the range i wanted. 

consistency in probe placement is key for repeatable readings so i made some plastic and wooden jigs to help with that. 

[Guillermo Suar]

I used to build a Gauss meter for slot car use. If I needed one now I would go to something like the one linked. I could never build it for that price and with the Hall effect sensors you can get in the regular electronic stores you cannot get to the range that one has.

[SpeedyNH]

agree that range was indeed a big issue. things have come a long way since then, but what i built fulfilled my needs at the time.  

[Phil Smith]

How about a pressure sensor? If it could somehow be made to work it seems you would need nothing more than the sensor and a multi-meter.

 

https://www.ebay.com/itm/264562222914

[Paul Lindewall]

Finally decided on getting a "Peter Meter". As long as I have a baseline reading average of various cars, it's acceptable.