TORQUE:
· Motor torque is directly proportional to current, double the current and the motor
torque will double.EFFICIENCY:
· At nominal supply voltage, maximum motor efficiency (of around 82%) occurs at
about 1/3 of maximum power output (refer to manufacturers data). At other
operating points efficiency is lower, down to about 55% at full power and down
to zero if the motor is stalled. Check the manufacturers specifications for your
particular motor.
OPERATION AT OVER-VOLTAGE:
Operation at Over Voltage is common it gives the following general advantages;
· At over voltage the motor is capable of producing more power than possible at
nominal voltage. We tested a Faulhaber 2224 6 Volt motor nominal 4 Watts at 12
Volts with 14 Watts input and obtained 9 Watts output at 14000 RPM. The
motor failed after this test. Note the efficiency at this point was only 64%.
· In general, operation at over voltage tends to hold motor power output and
efficiency up at high levels over a much wider RPM range than obtainable when
operated at nominal voltage. This means in practice that selection of gear ratio
and frequent gear ratio changes to keep the motor operating at near maximum
power and efficiency are not required as frequently.
EXTREME CAUTION: Remember any overload will reduce motor life and have the
potential to cause permanent motor damage or destruction.
Handle your expensive motors carefully.
CRITICALLY IMPORTANT : NEVER TEST A MOTOR AT OVER VOLTAGE
USING A POWER SUPPLY THAT IS NOT CURRENT REGULATED SIMILAR TO
A SOLAR PANEL.
A solar panel is a constant current device so is in effect power limited and can therefore
not supply unlimited power to the motor, consequently the chances of burning out the
motor is reduced compared to a battery or power supply which can supply very high
current.
The book ‘Model Solar Cars: Optimising Their Performance’ by Mr. Stan Woithe
contains a lot of useful data on motors and their performance. This publication is
currently out of print but an updated version is being prepared and when completed will
be published on the SA web site.
6 Weight
For best performance, keep weight to a minimum. But remember, a super light weight
vehicle that falls apart and does not finish is no good at all. (See Appendix C on
materials for some strength to weight data for materials sometimes used in model solar
car construction).