[ScorpiusWireless]

So who remembers using a magnet Marshall many years ago? I do.

So the existing ones using scales or  a load sensor transducer.
But there are none on the market that measure actual gauss.
Seeing we have our hall sensor up and running and is part of the telemetry I essentially just need an MPD and a hall sensor to plug in.
The hall sensor is mounted under the track and runs off 12V.

It’s all plug n play too.

While we’re here let’s 3D print a platform to mount the car on. 

We have a spare data port and tacho sensor laying around let’s mount that too in the 3D printed platform.

But we will need a way to power it. Let’s go with users power supply but we include banana plug connectors and more importantly an LED voltage readout so comparisons all use the same power input.

Of course we will need a way to see results. Here we could use the OLED screen on data port 1 and hall sensor on data port 2 but then we cant have a tacho.

Optionally one could purchase the Scorpius dongle and use MPD telemetry and a laptop that see hall, tacho and speed PWM. That way we can have all 3. The advantage here is you can use the Scorpius Car Driver program to run the motor from PC as well using your mouse. Here one could include a platform at the rear of the unit for cleaning tyres. 
If the car already has an MPD installed just use your controller. If you do you’ll still need a screen so gets we can install 2 x MPD piggybacked to gain an extra data port. That way you can have the hall sensor, tacho and OLED all operating together. Or use the dongle and PC for visuals.
So I think 5 options are required. The first includes hall and OLED. 
The second includes tacho and OLED.
The third includes hall, tacho and dongle.
The fourth includes 2 MPDS not one, with hall sensor, tacho and OLED. 
The fifth is 2 MPDs, nop hall sensor, tacho, OLED and dongle. 
The MPDs motor drive can run an analogue motor. 
If the car is already MPD you will use the cars decoder to run the motor.
The MPD could also power rollers on a rolling road.

We have current detection hardware installed yet to be explored. We could possibly even show amps drawn.

It could be wired also to accept an analogue controller.

A potentiometer could be wired to one if the ports also to operate motor speed. Here you could sacrifice the OLED to get the port 

Amazingly no special firmware is required for this as all that is standard on an MPD chip with Scorpius Car Decoder firmware installed. All that is required is a 3D design and print for the platform and a nice 3D sticker and we have a “product”.
Again the MPDs hardware rich wireless board makes any pipe dream possible.

[Kevan]

How does the Gauss reading relate to measurable magnetic downforce on the track? 

We have a 25g magnetic downforce limit, what Gauss is that?

[ScorpiusWireless]

It will measure gauss not downforce.

[Kevan]

That's why people use magnet marshalls and home made devices with a small digital scale instead.

[ScorpiusWireless]

How does the Gauss reading relate to measurable magnetic downforce on the track? 

We have a 25g magnetic downforce limit, what Gauss is that?

Gauss is relative to downforce.
You set the gauss limit like to would set the weight limit.
I can equally use a pressure based I2C transducer if you like grams over gauss.
The scale method is pretty clever though.