Mars Rover Vehicles:
The Regulations are exceedingly liberal, effectively anything goes as long as it fits within an
A4 paper carton, only uses energy collected from the solar panel and has no stored energy at
the commencement of the race. This allows participant’s wide scope for design innovation.
Because of this it is incredibly difficult to give any sort of detailed advice. Following the
basics for good motor racing vehicles is about the best advice possible.
The following points are worth considering:
• High power to weight ratio.
• Highest panel power possible under the regulations.
• Lowest possible vehicle weight.
• High efficiency motor transmission and electronics systems if used.
• Panel as close to right angles to Sun as possible.
• Vehicle and its drive system able to negotiate the obstacles.
• Do test your vehicle on surfaces typical of the actual track.
• Carefully consider the top speed of the vehicle, a high top speed may cause the
vehicle to bounce over the obstacles and catch on the track divider or outer
edges.
As a starting point for your design project investigation included here are details of two Mars
Rovers which have performed adequately. They tend to be on the technical side, one using a
capacitor bank for energy storage the other using the energy as it is collected. Both are 4
wheeled vehicles with all wheels driven. There are other far simpler design that perform
adequately, one that comes to mind is all polystyrene using cheap hobby motors driving large
diameter polystyrene wheels with rubber bands. It does not have to be super technical or use
expensive components. Good design is the secret.
1 MARS ROVER THE “ MARTIAN MISFIT”
The design philosophy behind this vehicle was rather basic. It was constructed predominantly
as a demonstration vehicle to showcase the competition and encourage participation. It has
performed competitively and reliably for several years. The design stores energy in a bank of
capacitors so if the vehicle was stopped at an obstacle it will charge the capacitors and be
able to deliver a short burst of full power to overcome the obstacle no matter what the Sun
level. It does however have some shortcomings listed below.
• Much too heavy.
• Panel power low.
• A set gear ratio meaning speed was effectively constant at all sun levels, leaving
it vulnerable to other vehicle that could potentially have greater speed in high
Sun conditions.
2 `
SPECIFICATIONS:
GENERAL
Length
300 mm
Width
205 mm
Height
118 mm
Weight
1850 gm
Power
3.7 Watts (at 100% Sun)
Wheel Diameter 90 mm (over spikes)
Wheel Base
138 mm
Track
155 mm
Entry and exit angles 40 Deg.
DRIVE TRAIN MECHANICAL
All four wheels driven (Gear drive from motor to front axle chain drive between axles.)
Motor Faulhaber 2224 12 Volt
Gear ratio 165:1
SOLAR PANEL & ELECTRONICS
Solar Panel JAYCAR Cat.No. ZM 9018 3.7 Watts max.
Electrical / Electronics system:
Solar Panel output is fed to a 98000 uF capacitor bank, via an optimiser (BHHS V2) set at
15.5V.
A Scorpio maximiser (modified) connects the motor to the capacitor bank when the voltage
reaches 15.3 V, and disconnects the motor when the voltage falls to 9.5 V.
A 16.4 Volt Zener diode is connected across the Solar Panel to limit the Voltage on the
capacitors to this level as they are only rated to 16 Volts. For racing this zener is removed
allowing the voltage to rise above this value and thus store more energy.
Tests on this system gave the following. At 50 ma. input from the solar panel the capacitor
charge time to 15 Volts with the above system was 16 Seconds.
Without the input optimiser the charge time was 23 seconds.
PERFORMANCE: The following tests conducted on flat concrete.
% SUN
12
30
40
Run Time
Distance
Recharge Time
Seconds
Travelled m
Seconds
8.9
3.5
31
23
10.7
9
CONTINUOUS ( 5 m in 10 Sec.)
5
The distance travelled on one charge of the capacitors with no input from the panel.
At 16.4 Volt (Zener voltage)
3 M in 7.5 Sec.
At 19.5 Volt (Panel max.)
5.6 M in 11.23 Sec.
On thick grass 50mm long only covers 700mm at 40% sun before stopping.
3 Photographs showing construction details follow:
General side view.
Front view showing ground clearance.
4 Underside view showing motor to axle gear drive and chain drive between axles.
Underside view of solar panel showing electronics system.
5 Inside view showing motor and capacitors.
6 MARTIAN MISFIT II
The design philosophy behind this vehicle was to produce a vehicle with a significantly
different energy system, lighter chassis and superior performance to the MARTIAN MISFIT.
The main differences between these vehicles are much reduced weight and nearly double the
panel power with no energy storage, the energy is used as it arrives. There is also a quick
change gearbox with 3 ratios available enabling satisfactory performance from 10% Sun
upwards.
7 `
SPECIFICATIONS:
GENERAL
Length
300 mm
Width
210 mm
Height
195 mm
Weight
950 gm
Power
6.2 Watts (at 100% Sun)
Wheel Diameter 90 mm (over spikes)
Wheel Base
195 mm
Track
145 mm
Entry and exit angles 40 Deg.
DRIVE TRAIN MECHANICAL
All four wheels driven (Tooth belt drive from gearbox to both axles.)
Motor Faulhaber 2232 6 Volt
Gear ratio 133:1 motor to wheel full Sun in top gear
SOLAR PANEL & ELECTRONICS
Solar Panel Dick Smith 3 cell segments 7 complete plus 2 cells all in series 6.2 Watts max.
Electrical / Electronics system:
Solar Panel output is fed directly to motor through a Scorpio optimiser Modified for low
voltage operation set at 10.7 Volts.
Additional Solar Panel data: used for design calculations.
SOLAR PANEL: 7 Dick Smith 3 cell segments plus 2 cells tested on light box 15/5/07
Panel Temp ISC
19
0.647
35
0.676
OCV
14.0
13.4
Power @
6.2
6.0
Volts
10.96
10.7
Amps
0.570
0.561
ELECTRONICS SYSTEM: Scorpio modified for lower voltage and better performance. On
light box powered by panel detailed above and adjusted for max power output ie. set at 10.7
Volts.
Panel short circuit
Current ma.
100
200
300
400
500
Current into nearly stalled
2232 6 V motor
330
590
780
950
1200
% Sun
15
30
46
61
76
Motor torque
mNm Calculated
2.64
4.72
6.24
7.6
9.6
All the above tests done with panel temp about 34 Deg C Motor torque is in milliNm
8 PERFORMANCE: The following tests conducted on the actual track.
% SUN
Gear
Race Time
70
1
2
3
7.85
11.37
24.37
40
1
2
3
10.0
9.5
18.0
30
1
2
3
16.0
14.0
28.0
18
1
2
3
31.0
26.0
36.0
16
1
44.0
12
1
53.0
10
1
110.0
Comments
Tended to stall on grid
Tended to stop on rocks
Will not complete course
in other gears below 18%
Evaluation of the test results above together with visual information as to how the car was
running led to the following decisions.
Sun level below 25%
Gear ratio 1
Sun level 25% to 50%
Gear ratio 2
Photographs showing construction details follow:
9 Motor and gearbox sub assembly.
Body (0.4 mm 3 ply) under side view. Note central reinforcing for motor &
gear box mount
10 Underside view of vehicle.
Underside view of solar panel showing electronics unit.
11 Complete vehicle.
Gearbox close up.
12 13