ARM Architecture

Arduino robotics #2 – chassis, locomotion and energy


Arduino Robotics

Newbie robotics is a collection of article chronicling my first autonomous robotic construct, Clusterbot.  This construct is supposed to be inexpensive, comparatively straightforward and instructive.  The entire value of the construct is round $50.  

1. Arduino robotics – motor management
2. Arduino robotics – chassis, locomotion and energy
3. Arduino robotics – wiring, coding and a take a look at run
4. Arduino robotics – HC-SR04 ultrasonic sensor

In final weeks article on newbie robotics, we talked solely about motor management.  This week we’ll take a look at the fundamental construction and locomotive system of Clusterbot and put all of it collectively.

The chassis

The logical place to begin when constructing a robotic is to consider a chassis, or base, to construct your robotic on.  For my first robotic, I had a number of necessities.  It wanted to be low-cost, straightforward to make use of and spherical.  As this was my first construct, I actually needed to pay attention extra on the management circuitry and logic quite than the mechanical features.  Having the ability to simply and securely connect the motors was a precedence additionally.  

A spherical chassis is an ideal form for a differential drive robotic.  Mounting motors on both facet of a round body permits the robotic to make zero-radius turns by driving every motor in reverse instructions.  This additionally simplifies design, as the identical motors are used for propelling and turning the robotic.  

I selected to buy a spherical acrylic robotic chassis from Pololu.  This chassis is simply $6, and it’s pre-cut and drilled for mounting a gear-box motor, wheels and a caster for stability.  

Locomotion

The spherical acrylic chassis is made to completely match Pololu’s single chassis completion package.  For $18.95, this package comprises a twin gearbox motor, able to independently controlling two axles.  The package additionally consists of 4 wheels and two ball-casters.  Mainly, all the pieces we have to construct a primary robotic platform, in need of a microcontroller and motor driver.

Motors and Gearbox

Tamiya twin motor gearbox kit

The motors are a pair of Mabuchi 3v toy motors.  I used the included motors, however the gearbox can be made to suit a pair of upper voltage, decrease present motors – like these 6v motors which have a stall present of 800 mA.  These motors are a greater match for the TB6612FNG motor driver.  The 3v motors work, however the working voltage is close to the low finish of the minimal voltage of the TB6612FNG.  For those who go for the 6v motors, they’re solely $1.79 apiece.  At that value, no massive deal if you happen to burn one up by chance. 🙂

The no-load velocity of our motors is 12,300 RPM.  Whereas that is amazingly quick, at that velocity there’s virtually no torque.  We are able to use gears to commerce this extra velocity for torque, in order that the motors could have sufficient energy to propel our robotic.  The package I purchased comes with a Tamiya twin-motor gearbox.

The Tamiya twin-motor gearbox is a quite attention-grabbing package.  You’ll have to assemble the gearbox your self.  The included directions are fairly good.  You can too check out the video under to get an thought of what assembling this gearbox is like.  There are two completely different gear configurations to select from – both a 58-1 or 204-1 ratio.  

The velocity and torque of your robotic is a operate of the velocity the motor, gear-ratio of the gearbox, and the dimensions of the wheels you put in.  I went with the 204-1 ratio on the gearbox to verify I had loads of torque.  This ratio supplies a TON of torque – I believe 58-1 would have been adequate torque with much more velocity.  The most suitable choice would in all probability have been to make use of taller wheels with the 58-1 ratio, however these are the sorts of belongings you be taught in your first construct.  In the end, I used to be not very proud of how gradual Clusterbot was, nevertheless it did make it simpler to see how the management logic was working as soon as I had all of the sensors put in.

Wheels

Tamiya truck tire setTamiya Ball Caster

Lastly, I put in the included wheels and ball caster.  I discovered the wheels to be a bit too small for my gear setup, however they’re fairly top quality and the tires are very grippy.  Set up was straightforward, merely pushing the wheels onto the axles.  The ball caster is straightforward to assemble and set up.  When putting in elements in your robotic, you do want to recollect to maintain extra weight over the caster in order that your bot will not fall over.

Energy

After assembling the fundamental chassis, I mounted a 2 AA battery pack.  This battery pack will present the 3V energy supply that the motors are rated for.  The microcontroller and different electronics can be powered by a separate 9V battery.  The leads from the 2AA battery pack will connect with the VMOT and GND pins on the motor driver, as mentioned in Newbie robotics – motor management.  Additionally, you will now have to solder hookup wire to the 2 poles of every motor, as I’ve accomplished within the video under.  Zip ties assist immensely with cable administration, amongst different issues.

The microcontroller

Arduino Uno Microcontroller

I used an Arduino Uno because the microcontroller for this construct.  I mounted a prototyping defend on the Uno, which gave me a superb place to mount the motor driver and make numerous interconnects for the robotic.  As you possibly can see within the unique image of Clusterbot, I then used numerous items from certainly one of my child’s erector units to mount the Uno to the chassis.  

On reflection, I ought to have used standoffs to place a second degree on the robotic, the identical dimension as the underside degree.  The underside degree may have been used solely for the drivetrain and battery packs, whereas the second degree would have loads of room for all of the electronics.  These are the belongings you be taught once you construct your first robotic.

Stability

Outrigger on Clusterbot to maintain balance

I discussed this earlier, however stability is a key consideration for a two-wheel, one caster robotic.  I discovered Clusterbot balanced on his wheels and caster positive when at relaxation, however would tip over when altering path.  Because of this you see the 9 volt battery pack mounted on an outrigger – to get extra weight over the caster.  It ain’t fairly, nevertheless it works.

Subsequent time…

Within the subsequent article, we’ll make the connections to the microcontroller and motor driver, write some primary Arduino code, and take Clusterbot out for a take a look at drive.

Associated Movies

Assembling the Tamiya twin-motor gearbox 

Soldering hookup wires to the motors 

Credit: Images of the acrylic spherical robotic base, Tamiya twin-motor gearbox, Tamiya truck tires and Tamiya ball caster are used with the permission of Pololu.

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