I'm finally done with the ball caster wheel

The very last (hopefully) ball caster wheel

The final design uses a more simplistic approach than previous iterations. It incorporates only one through-hole turn slot, as opposed to at least two on previous versions, the reduction in tabs did not decrease the structural strength, moreover, it increased the soundness of the design as there were less weak points and the design did not protrude from the central rotation as much, therefore any forces on the caster wheel would have less of a lever effect on the acrylic. Another reason to reduce the footprint size was the fact that the original designs required large slots that would be a great distance from the central rotatory axis and they too far apart for the latest chassis design to accommodate.

It has been a few days since it was first laser cut and assembled and this version has withstood more pressure and force than any of the previous designs and it is yet to break, however, as I still only have one, I am reluctant to put it through a stress test to see how strong it really is. Although the material is white as opposed to the semi-opaque blue of previous versions, it is the same material and was ordered on the same day, so the increase of structural strength is purely design caused.

A side-on view shows that the ridges are still present

This design has a raised slot, meaning that the chassis would no longer be a flat bed and this would have to either be ignored, or more preferably, fixed another way. This would be likely to involve lowering the motor mounts at the back-end of the chassis, to raise the back-end of the robot. 

This design (v0.8) can currently be found on Dropbox.

Re-design of the caster ball wheel re-design

The even newer ball caster wheel

Yes, this is another ball caster wheel and yes also, it does look exactly the same as it did last time. However, it is actually ever so slightly different from the previous version (v0.3)

The main differences are that this has fewer ridges to help reduce surface area in contact with the ping-pong ball, therefore increasing the fluency of it's rolling. Also, the ridges are now deeper and more prominent, this is in order to to make them look more purposeful; the bumps on the previous version looked like they were were accidental, thus making it look like the part was poorly designed.

To help reduce the chance of it snapping, I have reverted back to the slots being deeper and therefore the design has more structural strength throughout. On the other hand, this would cause the robot chassis to be uneven again, as it would be sloped backwards. Unfortunately, it still snaps, even though it has a thicker structure at the bottom supporting the ball; I think the cause of the weakness now is the slot which turns in the centre of the platform, as this may be causing unnecessary strain on the design.

It still holds the ping-pong ball nicely

The design files for this version of the ball caster wheel (v0.4) can be downloaded from Dropbox, along with the previous versions of the ball caster wheel. 

Caster ball wheel re-design

The newest ball caster wheel

I have yet again re-designed the ball caster wheel, this time I incorporated bumps into the design in an attempt to reduce the surface area in contact with the ping-pong ball and therefore aiming to make the ball run more smoothly. You might also notice that this design has two bolt connections, this is to help reduce movement of the acrylic parts. I have also made another small edit in the design, this is to make it slightly stronger so that it wont snap as easily, however, it was slightly stronger, but it was still not strong enough and broke fairly quickly.

A side-on view of the caster, you can see the bumps quite clearly

The design files for this ball caster wheel (v0.3 - v0.1 and v0.2 are implemented in the chassis designs) can be downloaded from Dropbox.

Re-designed chassis

This is the second version of the chassis, including a menacing 'grill' on the front

Since I posted the feedback of the modular circuits and the chassis design, I have been working on an updated chassis. Here are a few images of the chassis, currently without any electronics.

Here is a list of updated design features:

• The chassis is both thinner and shorter as I have no removed dead space on either side of battery and moved the caster ball wheel move closer to the battery so that it can be shorter
• It now has a sectioned battery compartment with a removable access panel, so that the battery does not move or fall out unless you remove the panel
• The motor mounts have been moved outwards and altered slightly, so that the wheel can be pushed fully on and will not rub with the chassis
• An integrated 'bumper' has been added, which is designed to slide back and make contact with a touch sensor
• The ball caster wheel has been updated, so that the ping-pong ball is slightly less loose
• Slots have been added in the centre of the chassis layers so that wires, such as the battery connections, can be wired through to the middle section
• The orientation of the LDR mounts have been altered, to point slightly more outward
• I made the ball caster wheel mount have a thinner section, so that the robot is more level

The battery compartment with the panel...

...and with it removed

There are already some known issues with the current design:

• The centre support of the bumper prevents it from sliding backwards
• I think that the bumper could look slightly less menacing, removing half the supports may fix this
• The ping-pong ball in the ball caster wheel now has some play, however, when the robot is resting on it, it causes enough pressure that it will not move as freely, one way to fix this would be to add bumps (ribs?) to the contact point of the ball caster wheel as to reduce the surface area that is in contact with the ping-pong ball
• The mount of the ball caster wheel is now thin enough to break easily
• Friction on the bumper prevents it from moving backwards and forwards easily, this could be helped by adding a layer of paper to act as a spacer

A close-up of the front 'bumper'

The two versions side-by-side

This chassis design (v0.2) can be downloaded from Dropbox.

It's alive!

The very first working modular robot

As I have previously posted, I have now finished the current versions of the Edgebot shield and motor controller board and they're working correctly together. I quickly designed a chassis for the robot that would act as a platform for the electronics to be attached to. The design includes and integrated caster roller that uses a common 40mm ping pong ball as the main pivot, this is inserted with a little force and a reassuring 'pop'. Once this current design can still be improved greatly, for example, the pin-pong is very loose and rattles a fair bit when not in use, etc.

The ping-pong roller ball, still to be finalised, but working.

The main section of the chassis is made up of 2 layers, the first of which is the base, this is what the gear motors are mounted to and the battery mounting rests upon, while the front section of this layer is slightly obstructed by the roller wheel fastenings, it does contain space to put other sensors or parts.

The top layer currently only accommodates the stackable PCBs, the motor controller is fastened to the acrylic using four M3 bolts and some nuts. Then other layers are stacked on top of that to provide other behaviours to the robot, such as light seeking and object avoiding, whilst the motor connections could be attached to the motor controller permanently, the other behaviour modules' inputs are interfaced by right-angle headers pointing outwards from the board. You can then plug in the sensors as they are required.

The files for the chassis design featured in this post  (v0.1) can be downloaded from Dropbox.