Make it real !

The next step is to make Trevor real. We will use a 3D printer to turn the Solidworks model into a plastic prototype on which we will mount the Rooby kit.
We will then upload our program to the main board of Trevor and run test in order to adjust the program.
We will need a number of iterations in order to fine tune it.

Unfortunately, the 3D printer was broken and we have not been able to create our prototype.

Hopefully we will find a way to make it real ...

When Trevor met Rooby...

... a love story started...
We need to bring some intelligence in this fabulous rover ;-)
In order to achieve this, we will use an electronic kit from Rooby that is made of a main board, 2 motors, a battery case and 2 sensors.
The main board can be easily programmed using a software provided by Rooby: Rooby Pilot.
The program is created like a puzzle, putting together a series of actions and sensors.
The program can be tested virtually in Rooby Pilot. Once finalized, it can be sent to the main board via a USB cable.

Here's our program:

Its logic is "move backward and change direction"

• Trevor moves forward (driving motor on)
• IF one of the 2 sensors of Trevor hits a wall (or a corner) THEN
• the driving motor is inverted, Trevor goes reverse for x seconds
• the driving motor stops
• the direction motor rotates the front wheel of x degrees clockwise
• the direction motor stops
• the driving motor goes reverse for x seconds
• the direction motor rotates the front wheel of x degrees anti-clockwise (back straight)
• the driving motor goes forward
• Trevor changed direction and moves forward again till it hits a wall again and re-applies the same logic (move backwards and change direction)
• ELSE Trevor continues to move forward

Remark :

• We equipped Trevor with 2 sensors (right and left) in order to run different actions depending which sensor is activated. When the left sensor is hit first, the direction will run anti-clockwise in order to move Trevor away from the wall. The opposite action runs when the right sensors is hit first.

Building a 3D model

We designed the new version of Trevor using a 3D modeling software (CAD: Computer-Aided Design). We used "Solidworks" to achieve this task. Solidworks is a very intuitive and easy to use software. We 3D-drew all the parts of Trevor then we assembled them (virtually).
The result of this work is:

The main parts of Trevor are:

• a chassis - this is Trevor's skeleton
• 3 wheels - 1 front (motion and direction), 2 rear (stability)
• 2 front sensors - switches - when one of the 2 sensors hits the wall, this launches a specific series of actions
• 2 motors - the first one is use to get the front wheel in rotation, the second one rotates the front wheel (direction)
• a main board - to program Trevor's conditional actions
• a battery case - to provide electric energy to Trevor (motors and main board)
• electric cables to connect them all ...

Some news !

We have entered the next phase of our exploration. Now we are designing our next prototype using a 3D modeling software: Solidworks. We are progressing with this 3D modeling. Stay tuned, we'll share the result with you very soon ...

So what's next now...

Stay tuned, there will be new versions of Trevor...
We plan to equip it with a special board ... check it here: http://www.espace-rooby.fr/

Adding a brain to Trevor...

Improving the Solar Panel stand

The solar panel can't be adjusted. Let's improve the solar panel stand so that we can adjust it to catch a maximum of light.
Here's the new stand:

A detailed view:

And the stand in action:

Here's Trevor V5 ! Test and report

We positioned the switch at the front of Trevor and equipped it with an horizontal bar so that it can easily be activated even when hitting a corner.
Here's how it looks like now:

We also added an extra wheel at the back to stabilize Trevor when moving backward.

Let's test it now:

Objective reached, it works!

We can be very proud of Trevor (and of us... :-))

Conclusions:

• Trevor is greatly improved now with the addition of the reverse switch
• The basic frame of Trevor is simple, robust and light
• We can think about new improvements now, the first one being an adjustable solar panel stand

The reverse switch: Principle and Connection

The principle of the reverse switch is to allow 2 different circuits when being in position 1 or 2.
You can then connect a motor and ensure that the polarity is changed by switching from position 1 to 2.

It's easier to understand on the following diagram:

We checked the internal connections of the terminals of the reverse switch using an ohmmeter. This showed us that:

• in position 1: terminal 2 is connected to terminal 1 and terminal 5 is connected to terminal 4
• in position 2: terminal 2 is connected to terminal 3 and terminal 5 is connected to terminal 6

We then connected the solar panel and the motor as indicated on the diagram above, reversing the polarity at motor's terminals when changing switch position.

We're back with Trevor V5...

We decided to evolve our anti-block system because it would not fit very well for this new challenge.

So we selected an electric approach. We used an electric reverse switch. The principle is the following :

When the switch is in the initial position the rover goes forward and when the switch is in its other position the rover goes backward.

We used a recycled switch from a broken device. Let's think about the planet ;-)

Up for the next challenge...

Let's just replace the wall by... 2 walls!
and the challenge becomes:

"Getting a rover rolling along a straight line. When the rover hits a corner, it moves away from this corner."

Stay tuned, we're working on it!

Test and report on prototype V4

Here's what Trevor looks like:

Let's recap what the challenge is:
"Getting a rover rolling along a straight line. When the rover hits a wall, it moves away from the wall."

and we did it !

Here's the event as we recorded it:

Conclusions

• Trials and errors is crucial to finally get a prototype working. It allows to solve problems step by step.
• There's not a single way to solve the issues faced.
• Simple is better! It makes prototypes more reliable.
• Never give up!

Trevor V4's anti-block system: how it works?

The new anti-block system is made of 2 wheels positioned on each side of Trevor at the front.

The wheel #1 touches the wall first and forces a movement to the left. Then wheel #2 touches the wall. With the inertia and the speed of Trevor, the direction changes and Trevor moves away from the wall.

Here's how it should work... 

Let's try it now!

Prototype V4: A simplified version

With the learnings from previous versions of Trevor, we finally built a simplified, lighter version. Here is Trevor V4:

Trevor V4 has 3 wheels. The 2 rear wheels are directly connected to the motor and the front wheel is mobile (rotation).
The solar panel is mounted on top of Trevor in a dedicated frame.
The anti-block system can be seen at the front of Trevor and is made of 2 main wheels. We will describe it in a next post.

And as you can see, we are very proud of Trevor and we have installed Trevor's logo on the side of the main frame :-)

Test and report on prototype V3

The anti-block is now functioning very well. When activated, the right wheel is not driven anymore and the left wheel is then driven backward.
BUT... when we connect the motor, the torque generated is not strong enough to drive the gears and the wheels. So Trevor is not moving AT ALL! :-(

Conclusions:

• We have overestimated the power of the motor
• We have underestimated the weight of Trevor
• Trevor is too complex, we need to SIMPLIFY it !

Back to the drawing board... let's simplify Trevor and its anti-block system. On the way to Trevor V4...

Yet another prototype: Trevor V3

Here's Trevor V3!

We changed the anti-block system and added the solar panel on top. We also made the 2 rear wheels independent so that when the anti-block system is not activated, the motor drives the right wheel forward and when the anti-block system is activated, the motor then drives the left wheel backward.

Here's how the new anti-block system functions:

and the two wheels running independently:

Test and report on prototype V2

We made a series of tests without using the motor to validate the operation of the anti-block system. The various movements (translations and rotations) are transmitted. Nevertheless the system is quite complex and not really reliable.

We need to change the anti-block system.

A new prototype: Trevor V2

We built a new prototype made of Lego. We decided to equip Trevor with a new anti-block system that is reversing the rotation direction of one of the 2 rear wheels. The objective is to avoid to get Trevor blocked when hitting an obstacle.

We used gears and toothed racks to transform the translation of the front part when hitting the wall into a rotation that is transferred to the rear part where the rotation is transformed back to a translation perpendicular to the initial one. This final translation moves the back part of Trevor, aligning gears that reverse the rotation of the wheel.

Test and report on prototype V1

We equipped Trevor with a electric engine and a solar panel to get the energy. The electric engine is equipped with a gear that is driving the gear attached to the rear wheels axis. 

Results :

• Trevor is moving forward !
• The frame isn't rigid enough
• The front wheel doesn't rotate and is blocked
• The anti-block system isn't reliable

Conclusions :

• We need to change the frame from cardboard to a more serious material : we decided to try with Lego Technic ©. They will have the benefit to offer a variety of axis, wheels and gears that can be easily and reliably assembled together
• We have to find an other anti-block system : check next post...

From sketch to first prototype

We decided to use cardboard to build our first prototype of Trevor.

• Step 1 : We created the ovoid shape for the frame on a piece of paper.
• Step 2 : We cut this shape in a cardboard.
• Step 3 : We built the back wheels using cardboard too and fix them to the axis.
• Step 4 : We cut the frame to host the wheels and built the front wheel.
• Step 5 : We prepared axis binding.
• Step 6 : We tested our prototype. The wheels were too narrow.
• Step 7 : We enlarged the wheels.
• Step 8 : Our first prototype is ready.

1st Sketch

Here's our first sketch of Trevor.
We decided to equip Trevor with three wheels to ensure a good compromise between stability and connection to the ground.

V0.1 : the initial shape is a circle. There are two driving wheels at the back and one wheel at the front.
The front side and the back side can be swapped allowing Trevor to progress forward or backward.

V0.2 : we decided to change the shape of Trevor to an ovoid shape as an anti-block system. The anti-block system is supposed to allow Trevor to change direction when he will meet an obstacle. The anti.block system should not use any electric power.

Happy New Year 2014, TrevoR !