R/C Steam Tank (with Turret)

As before I based the look on Crabfu's steam lobster tank. I penciled patterns onto 0.032" (1/32") K&S Aluminum sheets, checked symmetry with a ruler, and started cutting. If you've the grip, the K&S aluminum is soft enough to cut using scissors. Otherwise use metal shears, coping saw, metal nibbler, etc... Keep a file handy for cleaning up sharp edges. After making one tail segment, it became the template for others. I curved the segments using a 3" PVC plumbing coupling as a form. I then trimmed the segments down to length. The end-most segment is ~7-1/4" in length. Others are ~1/2" longer, but set at an angle. The tail segments overlap so any given pair of segments shares one or two common mounting holes. Mahogany strips (1/8" x 1/4") give structure to initially hold the segments together.		Lobster Tail Sketch Lobster Tail Segment Sketch
Certain segments need openings for boiler fixtures & the funnel port. I eyeballed the location of these. Drill a starting hole, use a metal nibbler to rough the shape & file smooth. Final positioning of segments depend your boilers fixture locations. To preserve the "lobster" look I made sure to keep the top-most lobster shell "points".		Lobster Tail Shaping

Body Rear

For the front of the body, first I made a u-shaped piece from a 4"x7" 6061 aluminum sheet.

It covers the fuel tank & supports the turret. It has a 2-3/4" diameter hole (based on a Meccano ring gear) for clearing the fuel tank valve, turret gears, wiring to the turret, etc... The 6061 aluminum coupled with the steel ring gear makes it strong enough.

Designing the remaining front panels took quite a while to flesh out. Lots of prototyping with paper, cardboard & tape. ie: cutting, bending, taping a little back on, repeat, etc...

The sketch shows my final design. Once the side panel shape was final, I continued the curve onto the front-most lobster shell.

2-56 x 1/2" brass hex bolts, washers & nuts hold everything together except the front apron. It's held with #2 x 3/16" brass hex lag screws for battery access.

Body Panel Sketch

Gear Ring

The track fenders are made from 3" x 18" strips of 0.032" 6061 aluminum. I used the stronger aluminum here since fenders are exposed to abuse.

I used a bending brake to make a 3/8" flange on the inner edge & 5/8" on the outer. The chassis tracks are 2" wide, so that determined the center-width.

Removing a couple inches of flange from the front/rear allows shaping the fender. I sketched a smooth curve which ended on the outer flange, rough cut with metal shears, and filed the edges smooth.

Holes were traced from the Mahogany strips made when assembling the body & 3/32" drilled. I kept the Mahogany strips in the final build to add extra width & enhance the look. Loctite secures the 2-56 nuts during final assembly.

The hand rails are made from 15mm flat stanchions and 1/16" brass rod. The stanchions are placed every 2 to 2-1/4" along the fender, bending in before the headlights. Drill mounting holes, insert stanchion mounting tab, and twist with pliers to affix.

Holes for head/tail lights were marked & drilled. The headlights are STE162 Gimbaled & Fixed Clear Searchlights. The tail lights STE152 Bullet-Style Navigation lights.

4. Turret

A 3-1/4" diameter needle roller thrust bearing from eBay sits on the ring gear supporting the turret.

I fabricated an aluminum ring base with tabs for attaching the turret body. The outer diameter was determined by a 4"x10" sheet of K&S aluminum. The inner diameter matches the thrust bearing.

Upward bent tabs on the outer edge attach to the turret body. Downward bent tabs on the inner edge align the thrust bearing. Straight tabs on the inner edge are for idler gears & servo (see sketches). The gears keep the turret overall centered within the ring gear.

I reused a servo from the original tank here. The servo gear is cut from a 25T Meccano gear. It's 1/8" thick with a thin hub. A #1 hole was drilled about halfway through to fit the servo spline gear.


Turret Base Sketch

Thrust Bearing	Turret Servo Gear

The turret body started simple (a cylinder), but I didn’t like the look so added the curved gun port bump-out & rear box structures.

The front bump-out is three pieces. Two sides & a curved front plate. Either freehand or use a drafting compass to sketch the curves onto some 0.032" aluminum. 2-56 brass bolts hold it all together.

The turret top is made from 0.064” (1/16") aluminum sheet, with Mahogany strips glued on. To attach the top to the turret body, several L brackets from scrap aluminum are glued on.

Finishing touches involved bending some 1/8" brass u-channel to hide the aluminum, and adding railings. I eyeballed positions for 15mm stanchions (same as fenders), drilled holes, and fitted/soldered the 1/16th brass rod railings. After painting, the turret sides are adorned with lion crests taken from some brass buttons.

The gun mount is a 4-1/8" x 5/8" aluminum rectangle folded into a narrow box, with a tab for the gun elevation servo. It's folded & the joint JB-Welded. A 5/32" hole drilled through is for the gun pivot axle. When bending its important to preserve the 1/2" internal gap otherwise the gun barrel doesn't fit.

The gun barrel is formed from two pieces of aluminum tube. A 1/2" tube and a polished smaller 3/8" tube that slides smoothly within.

A solenoid sits within the larger tube, and pulls the smaller one inwards to simulate cannon fire. Combined with an ultra-bright yellow LED, WTV020-SD sound module & Railmaster DHB8 8-ohm 2W miniature speaker (w/enclosure), the effect is pretty good!

The solenoid proved annoying since it dropped the battery voltage enough to brownout/reset/disconnect the R/C receiver & controller logic. Some 1F capacitors & a current mirror for charging them fixed that problem.

Turret Unpainted
Turret Top		Turret Crest
Gun Port Sketch		Rear Housing

Gun Barrel Sketch

Gun Barrel Assembly