I've been collecting ideas for building a Mars Rover. This can easily cost a few thousand dollars so I'm not quite sure I'm willing to fund such a venture, but it's fun to dream (and plan).

Apparently lots of people have been inspired by the NASA Mars rovers, as there's lots of projects out on the Web. NASA has even created an "open source" robot project, with downloadable plans.

Design Notes#

Open Source Rover Patch (click to enlarge)

So far I've been scanning the cool robot parts at ServoCity for ideas for the steering mechanism and rocker arms. The scale and weight of the overall robot help decide the size/power of the motors and servos. It's a bit of a balancing act. I also want to, unlike most of the "civilian" designs, somehow tuck my motors inside the wheels or otherwise not have them hanging down near the ground as many/most of the rovers I've seen seem to do.

There's a huge impact on ground clearance if your motors are down there banging into rocks and such. The difficulty seems to be locating some suitably deep wheels. I can't imagine simply 3D printing them, as plastic wheels wouldn't last very long on rocks or concrete. I want a robot that can actually roam outdoors. Also, unless the motors have durable ball bearings protecting the shafts, there needs to be some significant insulation between the motor shaft and the shocks that the wheels will create as they go over rough surfaces. Unless the robot is only going to run indoors, and then what's the point?!

The basic idea is this: six wheels, all 180-200rpm ~25mm high power motors with shaft encoders. The two center wheels are driven but not steerable. The four corner wheels are mounted on ServoBlocks so they can be steered. Rather than a Rocker-Bogie, we opt for the simpler Triple-Rocker. This requires two identical rockers on the sides and one almost-the-same rocker arm at the back, each with dual ball bearing mounts. There are no differentials or connections between the rockers (as in the Rocker-Bogie design).

There will be three pairs of motors, three dual motor controllers, and three batteries. Basically three separate systems, with two I2C isolators communicating between. The front and back motor/controller pairs (with the steering) are effectively identical. The central system won't have the steering, so that's where we'll mount the controller (likely a Raspberry Pi) and the rest of the sensors.

Rocker-Bogie vs. Triple-Rocker Design#

The ExoMars (and ExoMy) robot uses a simpler "Triple-Rocker" design.

Someone-Else's Specifications#

I'm going to (initially) steal the specs from the JPL Open Source Rover Project, as a point of reference. Their robot is a bit larger than I'm planning and has an estimated cost of around US$2500, and that's certainly at the upper limit of my budget. But it's a start.

AttributeValue [imperial]Value [SI]
Weight28 [lbs]12.7 [kg]
Footprint24x14 [in]60.96x30.48 [cm]
Battery Capacity5200 [mAh]5200 [mAh]
Battery Discharge Rate8 [A]8 [A]
Nominal Current Draw1.2 [A]1.2 [A]
Operating time5 [hrs] (continual use)5 [hrs] (continual use)
Approximate Max speed68.8 [in/s]1.75 [m/s]
Maximum 90 deg vertical scale12 [in]30.48 [cm]
Maximum height differential between sides14 [in]35.56 [cm]
Communication (in this guide)Bluetooth app (Android only) and Xbox Controller 
Cost (*)$2,500 

Initial Specifications#

Qty Item Unit Price (NZ) Price (NZ) Vendor Reference
3 ThunderBorg motor controller $73.00 $219.00 PiBorg https://www.piborg.org/motor-control-1135/thunderborg
6 wheels $30.00 $180.00 misc
6 47:1 Metal Gearmotor 25Dx67L mm HP 12V with 48 CPR Encoder $53.00 $318.00 Pololu https://www.pololu.com/product/4845
4 steering assembly: ServoBlock, servo mounts (est.) $42.72 $170.88 ServoCity https://www.servocity.com/standard-hub-shaft-servoblock-25t-spline/
4 2000 Series Dual Mode Servo (25-2) $47.00 $188.00 ServoCity https://www.servocity.com/2000-series-dual-mode-servo-25-2/
3 rocker assembly (est.) $50.00 $150.00 ServoCity/misc
1 Adafruit 16-Channel PWM / Servo Bonnet for Raspberry Pi $14.19 $14.19 Adafruit https://www.adafruit.com/product/3416
3 Makita Battery Li-Ion CXT 12v 4.0Ah $136.56 $409.68 Toolshed Petone https://www.thetoolshed.co.nz/product/8478-makita-battery-li-ion-cxt-12v-4-0ah
2 12V max CXT® Power Source w/ USB port (YL000000003) $95.00 $190.00 Toolshed Petone https://www.makitatools.com/products/details/YL00000003
1 Raspberry Pi 3 - Model B - ARMv8 with 1G RAM $35.00 $35.00 Adafruit https://www.adafruit.com/product/3055
5 Pololu Carrier with Sharp GP2Y0A60SZLF Analog Distance Sensor 10-150cm – 3V $18.47 $92.35 Pololu https://www.pololu.com/product/2474
2 Adafruit ISO1540 Bidirectional I2C Isolator - STEMMA QT / Qwiic $12.76 $25.52 Adafruit https://www.adafruit.com/product/4903
1 chassis (est.) $50.00 $50.00 misc
Total (not including shipping) $2,042.62


Tags:  Mars Rover