PIXIEDUST

TYPE-0 was good for a while and proved a walker could be built, the problem was it was slow (as walkers are) and didn't really have a good weapon until WS8 and even then it was a lifter. After 5 years it showed it's age. Since the rules allow ant person to have 3 ants in total and only 2 rollers this meant I had a space for a walker, enter Pixiedust.

I decided to put a semi-decent weapon on it and currently there is a lot of talk about full body spinners, some have been built in the past such as War Pog but never did too well as the spinner never had enough power behind it, really you want lots of power and weight behind the spinner so it doesn't stop when it hits anything.

 

I started with the main dome for Pixiedust, this is a 4" injection moulded hemisphere from EMA model supplies, on it's own it weighs 37g. That leaves (225-37) 188g for batteries, servo's, Rx and the walking mechanism. I started with this and Lego came to the rescue:

The first picture shows a single foot powered by 2*HS55's which were the lightest servo's I had around at the time. This worked but it was very unstable and either fell forward or back. I then progressed to 2 legs each side with the middle of the base acting as a middle foot and this worked perfectly but didn't have much grip.

 

After this I went for the rest of the parts:

GWS mixer

GWS 5A speed controller

Hitec Feather Rx

2*Saturn 62 servo's with GWS mixer

EMA 4" hemisphere

Aluminium weapon for attachment to dome. Made from cutting down aluminium L section, 5g each

 

Part Weight
Saturn 62 6.2g each (stock although weight saved by shortening wires and soldering directly to the mixer which saved around 3g)
GWS mixer 4g
Hitec Feather Rx 10g
Speed 280 43g (40g by cutting holes in the case with a dremel)
Speed 300 50g
Dome 37g
Batteries 300mAh 4 cells=31g, 5 cells=38g
GWS 5A speed controller 5g
   

At first I was going to use the HS55's and I modified them by moving the electronics board so instead of a rectangle they looked more of an L shape so I could mount them back to back, the problem was they were a bit slow and weak. I then found the Saturn 62's which are perfect and very easy to modify and there is no wobble on the output shaft.

 

For power I tested a Speed 280 and speed 300, both ran using 2A and 5A GWS speed controllers and with 4 or 5 cells. With weight reduction I managed to reduce the 280 down to 40g from 43 but I was concerned about the lack of a splined output shaft as it tended to slip when I tested it using a gearbox. One thing I did notice was with the dome once full power was given the speed controller tripped out and stopped the motor for about 2 seconds while it was required to reduce power to 0 then increase again, this was fixed by going to 5 cells from 4. With the 300 I couldn't reduce the weight due to the fact it's hard to take apart although the output shaft has splines so it slips less and also spins at 29,000 rpm as opposed to the 280's 14,000. To get the torque I had to make a gearbox and used some parts I had from an old Tamiya car:

This shows a side profile with the motor, gears and final top bit to attach to the dome

This shows the 3mm plasticard after weight reduction saving around 3g

 

Top shot, holes were cut using dremel drill stand with router bits

For the final speed of the dome:

motor speed = 29000 rpm with 8 tooth pinion

yellow gear=28/10 tooth

Green gear to output shaft=32 teeth

(28/8)*(32/10)=11.2:1 gear ratio, thus output rpm = 2589 rpm

Dome diameter = 4" (102mm)

Dome speed = diameter*rpm/336 = 30.8 mph (approx 13.5m/s)

This is without working out the efficiency of the motor and the diameter of the dome including the blades.

 

As for the dome:

Basic dome with single blade

2 blades with shorter tabs either side

Blades attached to dome with countersunk bolts from inside the dome

Side shot, black tape is for effect

 

Once the dome was built everything else had to fit inside which was very hard in the end:

Base made from 3mm plasticard with additional outer support ring. The black circles are rollers for the dome to rub on

Lego block inserted for the gears to be attached too and supports added for the gearbox to rest on

Servo's added with lego gears

Feet added

Foot showing the part that connects to the lego gears and the base

Bottom of Pixiedust showing the middle foot which doesn't move

Middle foot showing space for battery that slides in at one end

 

Lots of dycem as once the dome spins it tries to rotate the ant

Final shot of base with feet

Above I mention rollers, these are required as the dome spins and doesn't (well shouldn't) touch the inner base although in testing it did so the rollers are required to stop Pixiedust destroying itself. The dycem is required to add grip for 2 reasons, firstlty to sop it being pushed and secondly as the dome spins and gets to 1/2 power it tries to rotate the ant due to a gyro effect, the dycem gives a bit of extra grip to stop this happening.

 

At the time of buying the main dome I also brought 2" domes (I was thinking of building a 1/2 scale dalek), a 3 3/4" dome that fits inside the 4" one and a clear 4" dome that looks good and was there to make sure everything fit while I was testing.

And this let to the final thing:

Some work needs to be done such as tidying up the wires and soldering the motor in. The Rx and speed controller are at the top next to the gearbox, strangely there is hardly any interference from the motor although I did try to put all the electronics as far away as possible.

 

In testing the maneuverability isn't as good as TYPE-0 and it does slowly plod along which isn't bad. Once the dome spins it doesn't walk to well but for the majority of the time the dome will only be at 1/4 power ticking over till the enemy approaches then bang straight upto full power.

For testing the dome I rolled my solder reel into it and it threw it across the desk and the dome didn't slow down, it also threw a cardboard box off by desk but only put a small hole it in. Currently the blades are blunt and it does more damage from shock rather than real damage. It will be fun seeing it in action against the other FBS (full body spinners).

 

Update

Pixiedust has changed quite a bit since last time, here are the pics first:

The feet were the first thing to change as the Lego gears kept skipping resulting in the feet getting locked up. I could have fixed it but turned Pixiedust into a plodbot rather than a true walker. You can see in the 2nd picture above the foot attached to the servo horn, it works ok but the Saturn S62s aren't really upto the job and I have managed to strip gears in the past. The bas of Pixiedust is one huge foot coated with Dycem which makes it hard for an opponent to push it around.

One of the issues is when Pixiedust walks it rocks backwards and forwards, this means the blades can never be made to be near the ground. The way they are bent means that they could be quite a way in the air allowing an opponent to get underneath. A 2nd set of smaller blades were added pointing downwards which helped a bit. The blades were also changed from aluminium to steel but this was too soft so was replaced with titanium. The only downside is that titanium breaks when you try to bend it sharply.

To reduce weight the 5g mixer was removed and now the Tx provides mixing facilities.

The dome itself was replaced when another ant got underneath it with a spinner and cracked it.

The Speed 280 motor was replaced with a tuned Team Orion motor which gave extra speed and power. In addition the NiMh batteries were replaced with high capacity 7.4V 640mAh Li-Poly batteries which only add to the destrutive power of Pixiedust.

Well almost. Since Pixiedust's first outing at AWS 10 antweights have become far more dangerous with brushless motors and some working at 11.1V Compared to my brushed motor at 7.4V Pixiedust is completely outclassed.