MB Slot Universal Motor Tester
Published: May 1, 2008

MB Slot Universal Motor Tester




Hi to all.

We’re going to try the MB slot universal motor tester.

The tester in composed by: a clear plastic structure designed to block the motor during test, an L form cylinder axle, capable of pushing over a precision balance.



With this system we’ll know with good precision the torque value of a slot motor, using the motor “force” pushing down over a balance a L shaped axle, adding some computes; in few words we’ll try a locked rotor test and we’ll measure the motor torque [expressed in g x cm].

The assembly is simple and instructions are clear; you’ll obtain a result like our photos.





Next phase: position the motor over the clear plastic support and block it with the cotters , position the balance under the plastic support and adjust both measuring unit and tare.



With an M2 type key, lock up the L shape support over the motor axle with the L pointing toward ground and adjust tare again (best vertical axle length:2,2mm).


The system it’s ready to use.


Necessary instruments

Adjustable transformer:

We’ll feed our motors with 3V voltage for a short period ; higher voltages will disrupt the correct balance readings ,depending on the relation between torque and absorption current; this will also cause damage to our motors, because @12V with blocked rotor the motor absorbs a greater current and manifests great losses due to Joul effect, manifesting a great temperature escalation therefore damaging the motor.

Over the balance you’ll read lower torque values and smoke from your motor!

We’ll use a 3V voltage with the method described.




Many adjustable transformers don’t give the exact voltage output described, and this will affect our measurement.



With over 3V and make the reading; once this, if you want the motor torque at 12V, simply divide 12 by the value you found on the test and remember this result.

Eg: I want 12V torque and my transformer ,once put to 3V, outputs 3,34V.

The operation is 12/3,34, which reveals to be 3.593. I write this value over a blocknote.


Test Procedure

  1. Lock up the motor over the plastic support in a plain place
  2. Lock up the L shape axle on the motor axle
  3. Position up and switch on the balance
  4. Measure with your tester the Voltage output of your transformer and write this value
  5. Make 12/ (exact voltage output) and write this value eg: 12/3,593 = 3,34
  6. Feed up your motor with the transformer you set ,maximum 5 seconds and read the balance value
  7. Multiply the balance result by 3,25 (the torque arm) and by the value you obtained with 12/(exact tranf.output).

Eg: I Read 18 g over the balance, I multiply it by 3,25 cm (torque arm) and by 3,34 (transformer ratio) =210 [g x cm].


Our Test

We tried this tester with two motors: an Mb slot GNIK 21k and a Scaleauto 35k.



We obtained the following results:


Balance reading [g]

Arm [cm]

Tranformer ratio

Torque [g cm]

Scaleauto 36k





Gnik 21k








We tried other motors finding values very near to the productor’s declared. Worth noting that every motor is different from the other, as we found different torque and rpm values from two or three motor of the same type.

This tool is very useful knowing the properties of our motors, even when declared , as these productor’s values should be taken as indicative and not exact .


Hope this was helpful


Article submitted by MB Slot, originally published by Torquemadaslot.it


Discuss this article in the Forum!