Drivetrain
Motors
PimpMyMOD has great source of information on motors. Rates almost all the motors available out there.
All motor specs Don't remember where I got this, but is quite useful. (Let me know if anyone knows where the real link is)
Stock motor has 70 turns. Anything less than about 50 turns require upgraded MOSFETs to prevent burning out the FETs.
No matter what the motor, if it is stalled, and is given full power, it will likely burn the FETs. As the motor turns, it acts like a generator and puts out a reverse voltage that work against the battery. As a result, less current flow thru the motor. The faster the motor runs, the less current it takes. Obviously, the more efficient the motor work as a generator, the more reverse voltage it puts on the battery which limits the current flowing thru the motor, and therefore the speed. The more winding a motor has, the better it act as a generator. The more powerful the magnet, the better it is at being a generator. A low winding motor is a poor generator, so motor runs faster. However, because it has less winding, it takes more current.
The PN websites gives some basic motor performance measurements that allow the user to plot out motor performance graph. Electric motors are pretty linear device, so assuming that motor characteristics, one can estimate motor performance if given no load speed, no load current draw, stall torque and stall current draw and testing voltage which I assume to be 4AAA batteries or 4.8V.
Here, a straight line is plotted based on info. given on the PN web page. No load rpm is on the left side where torque generated is 0. At bottom is the stall torque where rpm is 0. Between the two points is an assumed linear line.
With some more math, efficiency can be calculated. Input power is the voltage times current. Voltage is 4.8V. Current is assumed to go up linearly between no load current and stall current. Output power is torque multiplied by rpm times 2(pi) divided by 531.0448.
Anima II has the lowest number of turns at 33 turns. It also has the highes efficiency. Many factors affect efficiency. In this case, my guess is that lower number of turns means less winding resistance so higher efficiency. All these motors have better efficiency than the basic Mabuchi FA-130 motor has about 45% efficiency.
Motor Pinions
Use 9 teeth pinion for stock and 10 for modified. The 6 and 7 teeth will give longer battery life, but are too slow. After running the car for a while, you will find that the pinion gear on the motor wears out quite fast. For me, for a modified car, after couple of battery charges, the nice silky fast silent running is gone even with the delrin pinion. About 10 battery changes latter, the gears starts to make slightly more noise. After maybe 30 runs, there is noticable wear on the pinion and significant noise. There is also some drag in the drivetrain as the pinion wears down.
There are some pinion options. PN racing makes an aluminum pinion that wears better than their delrin pinion. The aluminum one does have slightly more friction than the delrin ones. HPI racing makes a steel pinion that should last the longest. It only comes in minimum size of 8 teeth on up. That should fit mini-z application. The HPI pinion fits the mini-z perfectly mesh properly and has a larger 1.5mm set screw that makes it less likely to strip than the PN racing aluminum one. I will be trying the HPI next to see how long the wear is. I decided to also permanently lubricate it with a dry film lubricant to see if the friction can match that of delrin. The HPI steel pinion with dry lube may be the ultimate pinion for mini-z. Slightly heavier, but should be worth the hassle free performance. Stay tuned.
Update on HPI Racing steel pinion. The HPI pinion confirmed that the mini-z gear pitch is .5 module. The HPI pinion was very very quiet. With the dry lube on, the car glides across the track. The dry lube did wear out after about an hour of running. However, the steel gear wears very slowly. I have been running the car for maybe 10 battery charges. The gear train is still quite quiet. There is no noticable wear on the pinion. It is definitely better than aluminum pinion and delrin pinion. I am quite satisfied with the HPI pinion. Unfortunately, the RS4 is an obsolete car, and will probably be phased out pretty soon. Don't expect the pinion to be on sale for very long.
Update 4 months latter. I have been using the same HPI steel pinion for 4 months now on a stock car with Speedy 05 motor. There is hardly any wear on the pinion and the diff gear. This set-up has been trouble free. It might not be the lightest in term of rotating weight or the least friction, but is the most maintenance free.
Pitch conversion chart: Mini-z motor uses a .5 module pinion with 2mm hole.
http://www.engineersedge.com/gear_pitch_chart.htm
