Starting in 2019, Racing to the Future™ adopted a new rule restricting the Ohm rating on armatures, as a means to reduce overall costs in building cars for competition and to assist in balancing performance limits. This rule still allows Student Racers to design and build their cars with only a handful of restrictions and keeping the costs at reasonable rate.
After much consideration, the Racing to the Future™ officials decided to follow most professional “Super-Stock” restrictions, and limit the armature Ohm rating to 5.8 Ohms per pole or higher. This is the recognized baseline for “stock” armatures. Armatures may be balanced and commutators can be trued. This is referred to as a “Hot-Stock” armature. These are permitted, provided they meet the Ohm rating limit of 5.8 Ohms or higher.
Here is the current armature rule from the 2020 Racing to the Future™ rule book:
3. Armatures (Motor) CANNOT measure less than 5.8 Ohms per pole in resistance. Any armature that measures less than 5.8 Ohms per pole will not pass technical inspection and will not be allowed to compete. See the “Parts Guideline” for what parts may be altered or changed. EXCEPTION- Lifelike T-Chassis cars in stock format will be permitted to compete. However, the Lifelike motor in the T chassis cannot be used in other chassis/cars.
A Student Racer may still modify the other parts of the slot car to gain performance increases, so long as they meet the requirements listed in the Racing to the Future™ rule book
How to Measure Your Armature Rating
You will need to use a Volt/Ohm meter to measure your armatures Ohm rating. The meter can be digital or analog. We will be using a digital meter for this demonstration. All entries will go through this process during Tech Inspection, before the racing competition. This is how you can measure your armatures and record their Ohm rating.
The picture above shows the two types of slot car armatures. The armature on the left is an example of an “inline” design. The armature on the right is a “pancake” design. Inline designs may be positioned in the chassis by bushings or bulkheads, or may part of a “Can-Motor” design. The pancake design is used in Xtraction, 4-Gear and ThunderJet type chassis. Both armatures function the same way, they are just different approaches to design. Let’s take a look at the parts that make up an armature.
The “pancake” armature on the left shows the 3 solder points you can test from. The “inline” armature on the right shows 2 of the 3 solder points you can test from. The solder points are where you touch the Volt/Ohm meter’s leads to, to get the proper Ohm rating from the armature. it is prefered that you test from the solder points, but you can test from the commutator plates. That is best avoided to prevent scratching the commutator’s plates.
The pictures below show each of the armature types being tested. The “pancake” armature shows a reading of 16.5 Ohms and the “inline” armature shows a reading of 9.0. Both examples are well above the 5.8 Ohm requirement and would be permitted to race. Make sure to test each pole. The poles should read within 0.1 Ohm of each other. Reading with large differences could mean the armature is damaged and should not be used. You should make 3 readings, one for each pole.
You now have the steps to take and what tools to use, to test your armature and to make sure your armature’s Ohm rating meets the rules for Racing to the Future™ competition.