by
Daniel J. DykeWe outline our articles so that you can reference the section in emails if you need help.
PART 1: BASIC DESIGN
PART 2: USING AND ENHANCINGPART 1: BASIC DESIGN
In ancient Greek one of the words for power was dunamis and we get several English words from it like dynamic, dynamite, and our word dynamometer. What is a dynamometer? A dynamometer is a device that measures power. For model car racing they are useful in comparing engines with one another to find the stronger of the two or in tech inspection to find that someone is cheating in box stock classes. This series of articles is on how to make and use one.
My first attempt was fruitless and discouraging. It involved the plans and software found at http://www.sci-spot.com/Mechanical/dyno.htm. The problem I ran into was never being able to get a suitable mouse to convert into a data acquisition device. The designer of the dyno's hardware and software was tight lipped about which brand of mouse worked. After killing many a rodent, I just gave up for a while and decided to wait until a proper one of those critters comes my way. I still have the mechanism on my workbench, but until I get the needed part it is just a paper weight.
The second attempt is not as elegant nor is it as scientifically valuable, but it does give relative values for what a motor will do. The basic design comes from Tom McNay and this article is written with his blessing. He also is writing an article on making a gauss meter which I hope will be out soon. There are many type of people in our hobby and Tom McNay is one of those creative thinkers who comes up with some really great and practical ideas on how to do things. Like me, he is not a great driver, but he does well because he builds good solid cars.
A. The Basic Theory
The first assumption is that all units of measurement are all relative. In measuring a motor's performance all I need is consistent readings and numbers that reflect relative values. What is meant by consistency and relative values? A measuring device has consistency if it gives the same results under the same set of variables. When all the variables are kept the same except the object being tested then we have relative values. This gizmo helps us compare one motor with another. If on our machine one motor gives a reading of 18.1 and the other a 20.3, then in some way I know the second motor is doing more work. If the testing device is made so that the amount of work required in the test can be increased or decreased then the data becomes more valuable as a broader base of data is accumulated.
B. The Basic Design
The basic idea is simple and can be easily visualized using or diagram. First hook two motors together using a coupler. MOTOR A is hooked to a power source and MOTOR B is hooked to a multimeter. When the power is applied to MOTOR A then MOTOR B becomes a generator and its output can be measured in volts or amps by the multimeter. The numbers then become our relative values for what the motor is doing.
C. Main Parts
1. The most important parts are MOTOR B and the coupler that hooks the two motors together. The reason these two are singled out is that they are the parts most prone to failure.
a. MOTOR B: A Mabuchi FK-130 that was in my parts bin was used as the generator. This variant of the FK-130 was a lousy motor for slot car racing because it turned only about half the RPMs of an NC-1. The advantage of this motor is that it is well made. It has carbon brushes and hefty bearings on each end that are accessible for oiling. It needs to have durability when testing a motor like a Falcon 4. You don't want it throwing windings or disintegrating a commutator. If I had to buy a motor then a Falcon would be the choice as that is the hottest motor on the market that is not overly priced.
b. The coupler is a piece of heavy fuel line tubing from the RC airplane store. One should take a Mabuchi motor to the store and find the tubing with the proper ID and the largest OD available. On my first attempt with a Slot Car Heroes FF10 the tubing twisted to nothing. Important data! A Fly motor ran fine with that same setup, but the SS10 destroyed the dyno's coupler. The second trip to the RC store netted this stuff that costs $.50 a foot and is able to survive the ravages of even a Falcon. If those of you who are local residents want some I will make up some packs for Ray and bring them to the store.
2. MOTOR A: This is the test motor. You should always designate a motor as your baseline motor and never use it except to start a day's testing. Why is this necessary? In my area the power from the wall fluctuates slightly and so this is just a way of setting the baseline for the test. I use a SlotIt V-12 and a Mabuchi FF-130SH.
3. Make sure the power supply produces at least one AMP of power. If you are going to test the really hot motors, make sure the power supply can handle it. The Falcon IV requires about 4 amps to run properly. Some motors will start with a low amp power supply but they will wind up slowly.
4. A multimeter can be purchased at places like Harbor Freight Tools for under $10.00. Mine cost about $4.00 on sale.
D. Practical Considerations
This is where all the parts are put together. First you cut a plastic sheet into a rectangle about 4" wide and 8" long and then put the two motor on it face to face. After this you take a thin piece of plastic (see the illustration) with a very straight edge and glue it to the plastic base on one side of the motors. The motors are then moved snuggly against the edge of this second piece of plastic and another piece of plastic was glued on the opposite side. These pieces of plastic align the motors and help hold them in place. A second block is then put on top of these two to give further stability to the motors.
The wires from the multimeter are cut to a usable size and soldered on to MOTOR B which was then hot glued in place. The coupler (the red part in the first illustration) is super glued onto the shaft of MOTOR B. The power supply now gets alligator clips attached to the two lead wires.
When all the glues on MOTOR B are dry the armature shaft of MOTOR A is slid into the coupler, but not glued in. One wire from the power supply was attached to the test motor. The multimeter was then turned on and adjusted to give readings between 1 and 50 volts. The test motor had to be held down with one hand as the other alligator clip was touched to the other contact of the motor. The two motors spin in unison and a reading appears on the volt meter. Did the multimeter register anything on my first tray? Yes, but I got negative readings. All I had to do was reverse the wires or just ignore the minus sign. What readings you get depend on the nature of your MOTOR B. Tom gets readings of 6-10 volts with his setup, but I get readings of 10-35 volts. Actually I don't care what Tom gets because all that matters is I can take a stack of motors and quickly tell which one is better. I found one Scalextric motor that was much worse than the other eight I tested. Guess which one is not going in my limited modification class IRL car?
Initial Results and Enhancements
A. The Art of Saving Junk. I have a large box of used motors that were saved even if they were dead or tired. I decided to go through these motors first to see if they were dead as I forget over the years the history behind their demise and so this will help me determine their fate. Each motor was numbered so they could be identified later if I needed them for a particular purpose. They were then tested on the tester.
1. Dead or "Tired" Motors: These are used for their salvageable parts. For example, on occasion you break those little metal solder tabs off an end bell, but if you have a good one in the junk bin you can change it and have your motor running again.
2. Cheap Motors: These are out of toys or appliances which often have the wire whisker brushes which wear out quickly. Parts from these are combined with parts from dead motors to make what I call "Frankenstein" motors. You can use these toy motors in one of two ways. The first is to put a good end bell on them. The second is to pull the armature and put it in a good can with a good endbell. I did the armature switch on a NC-1 and it now runs like a standard Scalextric motor which means it is hotter than a standard NC-1.
3. Tired Motors Needing Work: I have a NC-1 that produces three less volts than the others and so I am going to tear it apart, clean, oil, and reassemble it. How well this goes will be determined by the numbers.
B. Test Results from 32 Motors: These motors are the standard models unless otherwise noted. Some are mysteries to me and so I have no idea what they are, but still want to know how well they do as a good motor is a good motor. Why 32? Because that is what I tested. Others will follow as I get time.
Motor # Model Rating Comment Configuration 01 Monogram 21.7 Donated by someone who thought it was dead. Can 02 ? 29.8 Unknown origin and look but it is a screamer. Can 03 NC-1M 17.9 Armature replaced with one from a toy. EB 04 NC-1 12.8 EB 05 NC-1 10.9 EB 06 NC-1 11.9 EB 07 Evo 2 18.7 Can 08 Cartrix FX Sport 19 EB 09 Artin 11.4 Can 10 Artin 7.9 Can 11 Reprotec (Yellow) 11.9 Can 12 ProSlot (Red) 22.7 Can 13 Scalex 17.3 EB 14 Fly 19.4 EB 15 Fly 19.9 EB 16 Fly 15.4 EB 17 Scalex 19.4 EB 18 Scalex 17.8 EB 19 ? 23.8 Can 20 ? 19.3 EB 21 Fly 20.2 EB 22 Fly 19.2 EB 23 NC-2 14.5 Red Label Can 24 NC-2 14.9 Red Label Can 25 NC-2 14.5 Red Label Can 26 NC-2 15.1 Red Label Can 27 NC-2 16.5 Black Label Can 28 NC-6 19.6 Can 29 NC-5 17.5 Can 30 SlotIt Boxer 22.8 Black Label Can 31 VMG (?) 23.3 Can 32 NC-2 (?) 15.1 Can C. Tests from SCX Motors: I built a second dyno using an RX42 as the generator. The numbers should not be compared with the above numbers as MOTOR B is a different motor. We must always remind ourselves that this is for comparing apples and apples. The actual track performances bear out the validity of the numbers.
Motor # Model Rating Comment S01 RX-81 8.2 S02 RX-81 8.3 S03 RX-81 8.1 S04 RX-41 8.9 S05 RX-41 9.6 S06 RX-4 6.7 S07 RX-62C 11 S08 F-1 8.2 S09 RX-4 7.1
D. Potential Enhancements
1. Increasing the Work Load: Some motors work better under certain circumstances than others. I am putting a Kemtron motor in line with the generator so that the electrical output does something. Why a Kemtron? It is a substantial motor that I have that is huge by today's standards. Four motors from the above list have been chosen to see how they are affected by the increased load. If they are affected in varying degrees then the data is very important, but if the results are all consistent then the data has less value.
Spei Meliorum Temporum
