10. The Tail, Battery & Wiring

INTRO

The assembly of the rear legs (etc) was shown on the previous page (Page 9). This page shows the attachment of the tail components, the first stage of the wiring up process and includes the attachment of the battery.

These changes are located approximately where the arrows are indicating below.

(Nb an amendment to the design is to cut the tail into two halves which are joined by a section of threaded rod. This is explained at the end).

When completed it will look like this:

This stage is not very complicated -the wiring circuits are very simple- but fitting the wires is a little tricky due to space restrictions.

Nb. once the tail parts are in place we then focus on the neck and head components. We will return to the tail finishing off when we assemble the controller and lead.

PARTS

List of components presented in this page :

Tail base (53)
Tail middle section (54)
Tail rod, plastic: 8mm dia x 500mm
Battery (12V) + charger
terminal blocks, 3A (x2)
cable ties, black (x12)
cable ties, green (x9)
3mm heat-shrink tubing, red, 2:1, shrink ratio x 60mm
3mm heat-shrink tubing, black, 2:1, shrink ratio x 60mm
6mm heat-shrink tubing, red, 2:1, shrink ratio x 40mm
6mm heat-shrink tubing, black, 2:1, shrink ratio x 40mm
M3 socket screws x 12mm (x2)
M3 socket screws x10mm (x2)
M3 nuts (x4)
M3 washers (x2)
M4 threaded sleeve (x1)
M4 grub screw x 20mm (x1)

Nb one 12mm socket screw and nut should already be in place from a previous page (joins rear cage, tail base, belly rod and rear brace together).

Exploded views below (new 3D printed parts are coloured blue):

ASSEMBLY

The parts are shown below as they are assembled:

Note that this is a complex shape so a lot of support material will be needed when printing it. Take care when removing the support material.

**Tail base (53)** **with support material removed**

Tip: this was printed oriented as in the photo above with support material everywhere (not just on the underside). Take care when removing it. Make sure all the support material is removed from the nut cavities otherwise assembly will be difficult.

The first step is to remove the rear cage (9). This is held in place with 5 sets of fasteners. Do this by removing the four fasteners that secure it to the motor holders (green arrows below) and one more secures it to the tail base (53), belly rod (22) and rear brace (49) [i.e., these are all secured with a single M3 screw and nut at the yellow arrow below]. All of these fasteners should already be in place from a previous page.

Nb. in the photo below, the tail base (53) has already been attached but ignore that for now.

As can be seen, there is a space behind the crank wheels and this is where the battery can be housed.

Arrange the wires from the battery so they are facing upwards (yellow arrow above). Arrange them so that the ‘male’ output connector is on the left (orange arrow above) and the ‘female’ input (charging connector) is on the right (green arrow above).

As previously, please ignore the attached tail base for now.

The image below is an underside view and shows the battery secured to the space frame using cable ties (green in this case, but black would be better and the parts list at the top of this page includes these as black ties). Actually we have only supplied 100mm long cable ties in the kit so join two together to create longer ones (as shown at the yellow arrows below).

**Securing the battery with cable ties**

The rear cage (9) can now be re-attached.

The wires from the leg and crank motors (8 black and 8 red wires) will need to be routed to go into the opening of the base of the tail at it’s widest section (red arrow below) before this tail section is attached.

**Showing where the wires need to be routed**

Before doing this the wires need to be organised and prepared.

So, as this device will be skid-steered, the motors on the legs of each side must rotate in the same direction so that, when both skid-steer slider switches are moved forwards, the legs all rotate in the same direction and the whole device moves forwards (more on this on a later page).

There are thus three wiring circuits, two for the leg motors and one for the crank wheel motors. The motors are wired in parallel and for the legs, those on the same side should rotate in the same direction, as explained above.

Firstly for the leg motors…

Here is a simple wiring diagram for the leg motors circuits. These show the left and right circuits shown from above.

**Leg motors circuits (left, right) wiring diagram**s

Nb: the red / positive and black / negative annotation is just illustrative. It is easier when preparing them to just make them all the same in terms of soldering on the red and black wires and then to simply test them again once installed and arrange the wires accordingly. That is, the colour of each individual wire might be red or black but that does not necessarily indicate its true polarity.

Once the wires have been organised into pairs (there should now be 4 pairs, two for each circuit), slide a 30mm section of 3mm heat shrink tubing on each pair.

(*Ignore the terminal block for now).

Thus each set of two motors will be controlled by two sets of paired wires. Use a black piece of heat-shrink tubing for one and red piece for the other.

Nb, arrange it so that when completed the wires extend by about 150mm out the back of the device. That is, leave enough length on all the individual wires to route them tidily along the rods of the space frame and with c. 150mm remaining. The trick is to do it all methodically and use cable ties as you go. You need enough length so that it is tidy without pulling too hard on the wires but at the same time without having too much slack so that it becomes untidy which might result in a wire being yanked (especially if you manage to meet another device in battle!). Any excess length can be folded and fixed to the space frame with cable ties.

To join two wires, first remove c. 10mm of insulation from the individual wires and then twist them together and solder. Once soldered together and when cooled, slide the 3mm heat shrink tubing on until it exposes 6mm to 8mm of the soldered wires. The heat shrink tube can now be heated carefully until it shrinks onto the wire and grips it.

**Wire pair soldered and with red heat-shrink.**

Nb. a note about the use of cable ties. Generally black is best (or that is, to correspond with the colour of the main space frame). Later, the push-fit electrical connectors will be colour-coded so it would be best to avoid confusion by using just black. In places however, green ones can be seen. These are often temporary because sometimes it will be necessary to secure the wires out of the way but then later to re-organise them. In the end, if a cable tie is not the right colour this does not seem a problem unless it confuses the wire coding (more on this on a later page).

For each leg motors circuit of 2 motors, a 3 Amp terminal block is used. The prepared wires (as explained above) are attached as shown.

**Terminal blocks for the legs and biting circuits**

So, to summarise, the terminal block on the left above will supply power to the two left leg motors and similarly the one on the right will supply power to the right leg motors. Later, each side will be controlled by a slider switch (on-off-reverse) as part of the skid-steering system.

Power wires can be used now to test the circuits (as shown above). That is, attach to the terminal blocks to check that everything works and is wired correctly.

Next, the crank wheel motors….

There are again four motors but these are controlled by a single micro switch (instead of two slider switches). All of the motors are thus connected in parallel.

This is illustrated in the diagram below.

The four motors will therefore have eight wires, four black and four red (nb as mentioned above, these may not all be correctly wired -that is, in terms of re / black wire insulation- and testing will be needed). The wires need to arranged into two bundles of four wires so that when powered up, all the crank wheels rotate in the same direction.

**The four crank wheels and motors assembly**

Once organised correctly, solder each bundle of four wires together, cover in 6mm diameter heat shrink tubing (red, 40mm & black 40mm) and fix to the space frame in a tidy way, leave about 150mm hanging out of the back of the device.

Next, tail & terminal blocks…

So at this point the motors moving the left legs are now connected in parallel and the resulting two wires extend out of the back and are attached to a terminal block and similarly for the right legs. And the wires from all four crank wheel motors are wired in parallel and the two resultant wire bundles extend out of the back. This is shown below:

(Nb in the image above the tail base is also shown but in fact it has not been added yet -discussed below).

The terminal blocks will be attached to the tail base as follows.

Each terminal block will have a central hole c. 2mm diameter.

Drill this hole out to 3mm.

Insert an M3 nut between the screw tubes on top of the terminal blocks.

The terminal blocks are secured to holes on the underside of the tail base using the M3 nuts and M3 socket screws x 12mm, plus an M3 washer.

Thread the terminal blocks through the wide end of the tail base and into position above the holes so that the left hand one is nearest the wide end. Angle them as shown to permit access for the wires.

**Wide end of the tail base with terminal blocks attached**

Once the wires are installed correctly, locate three M3 nuts into the lugs on the tail base:

Tip: An M3 screw can be used to draw the nut into the lug recess as shown above. Nb first make sure any support material has been carefully removed and drill out the hole with an M3 drill bit.

The two lower M3 screws are 10mm long and are inserted from the direction of the yellow arrows as shown below.

**Underside view of the tail base lower lugs attachment**

This is a little tricky as the screws need to be secured from within the space frame.

The top lug is secured with a longer M3 socket screw which is already in place from a previous page as mentioned above. This secures several parts together: the rear cage (9), the rear brace (49) the belly rod (22) and the top lug of the tail base above.

**Green arrow shows location of the top lug screw**

**Showing the attachment of the tail top lug with tail base shown transparent**

Again this is little tricky to do. Tip: a long Allen key is helpful.

The Allen key needs to be long enough to reach from between the upper crank wheels as shown below.

**The long Allen key is used between the two upper crank wheels.**

Next….tail mid section...

The tail mid section is what holds the tail rod in place and as this is subjected to quite high forces it was decided to attach this using cable ties. This allows for some flexing.

The corners of the widest end have small nodules which key into similarly shaped recesses on the end of the tail base.

Attach the tail mid section using three cable ties of the same colour (preferably). First, position the item approximately and attach the cable ties loosely.

Once all three are in position, tighten them evenly and then snip off the excess.

Then rotate the locking parts of the cable ties out of the way.

It should now look like this at the back:

The 600mm x 8mm diameter tail rod is inserted into the hole at the narrow end of the tail mid section:

The next part of the wiring up is to create hand held controller, umbilical cable and the push-fit connectors.

But that is covered properly on page 14.

Amendment: cutting the tail in half

Before proceeding with the wiring (on P14) an amendment has been added.

This is needed for ease of storage and transportation. So, instead of a long, single piece of 500mm rod for the tail, two 250mm rods are screwed together.

(If you have access to a lathe then please skip the notes below about the drilling jig).

So the objective is to add an M4 threaded sleeve and an M4 grub screw.

The first step is to drill a 5mm hole 15mm deep in the end of the ‘female’ rod.

To facilitate this (if you don’t have access to a lathe), a simple ‘tail drilling jig’ tool has been designed:

For stability on the 3D printer bed, a base has been added which breaks off easily.

After printing the drilling tool, break off the temporary base and drill out the larger end to 8.5mm which will correspond to the diameter of the tail rod.

Make sure the end of the rod to be drilled is as square as possible using a fine-toothed file. Again ideally this kind of work is done with a lathe. Remove any burrs (or it may be hard to press it onto the rod).

The jig tool should now be pressed onto the prepared rod end.

Now use a 2mm drill bit in a suitable drill just to mark the end of the rod via the hole in the jig. Remove the jig and check for centrality. If it is not central, file off the mark and try again.

Once central, drill a pilot hole using the jig and then use a 5mm drill bit to drill a hole 15mm deep.

Press the M4 sleeve into the hole. A friction fit should be enough but it it is not secure use some Epoxy resin or superglue (but avoid getting the bonding agent on the thread).

**M4 sleeve pressed into tail rod section**

Repeat the marking and pilot hole drilling exercise described above on the other section of the tail rod.

Then drill out the hole to 3.5mm and 10mm deep.

Use a countersink tool or a larger diameter drill bit to create a countersink (Tip: if using a larger drill bit use the drill in reverse to avoid snagging). Once countersunk, run the drill bit through again to remove internal burring.

Use a 2mm Allen key to drive the grub screw into the hole so that it cuts a thread as it goes. It needs to protrude about 10mm from the tail end. As with the sleeve, friction should probably be enough to hold it fast but id not a dab of glue should hold it fast.