Introduction: R/C Steam Turret Tank

About: I'm an electronics design engineer, with a passion for blinky lights, shiny brass parts and live steam power. More of all three the better.

Fire, Water, Steam, Motion. A fun build of a r/c live steam powered tank with turret & gun.

I've always enjoyed live steam powered machines, but Crabfu's steamtoys inspired my imagination.

This is my spin, with dual engines for independent track control, a working turret, and simulated cannon fire action. The tank uses 100% live steam power for propulsion. Batteries only power the radio/controllers, lights and effects. It's based on an old Tamiya 1/16th scale King Tiger off eBay.


Yes, this uses flammable gas (camping fuel), fire and water to produce pressurized hot steam. The boiler gets hot, the pipes get hot, the engines get hot, the exhaust pipes get hot. You'll need to use a torch to solder brass & copper pipes. Burns & blisters happen easily if you're not careful. Whatever you do never modify or block the boiler safety valve. Always wear safety goggles & keep a fire extinguisher handy.

There is a lot to do. Let's get started!

Step 1: Supplies, Basic Materials, Tools...


Safety goggles & fire extinguisher always.


Screw drivers, Hex Nut Drivers, Allen keys, Pliers, Scissors, Metal Nibbler, Sheet Metal Hand Seamer, Hacksaw, Files, Square, Center Punch, Drill & Drill bits, Pipe Bender, and oh yes... a vise.


Soldering/Plumbers or Micro Torch, Flux, Silver Solder, Sandpaper.


Aluminum Sheets - 0.032" (1/32") and 0.064" (1/16") thicknesses

Copper Tube - 1/8", 5/32", and 3mm sizes

Brass Square (5/8") & Round rod (5/16" & 1-1/4" sizes)

Brass 1-1/4" Round tube

Brass 1/8" U-Channel

Mahogany Strips (1/8" x 1/4")

Union cones, Union nuts, Pipe nipples

Meccano Gears (15, 19, 25, 38 & 57 tooth), Ring Gear, Axles, Collars, Strips

Zinc-Core Candle Wick

Various & sundry screws/bolts/washers/nuts/etc...

Loctite Thread Locker, Cyanoacrylate glue, JB-Weld

Engine enamel paint (to handle exposure to heat, water & oil).

Step 2: Major Elements: the Chassis

A 1/16th scale Tamiya King Tiger is the starting point for the chassis. Other than a few gears, the base chassis is all aluminum & steel. So no worries about heat melting anything. The original plastic body & turret won't be used.

You could likely use a plastic tank chassis, if you insulated the plastic from the boiler (ie: wood or fiberglass insulation). A metal chassis avoids such concerns.

Another option is making your own metal chassis, and using tracks from someplace like Lynxmotion. However, you'll need some extra reduction gears. The KT front gearbox ratio is 6.25:1.

Step 3: Major Elements: the Power Plant

The boiler I used is a MaccSteam 3.5" diameter Horizontal Marine Boiler. Nearly 7 inches of heavy copper goodness (excluding burner). It takes up half the available chassis space. The boiler comes fully equipped, with pressure gauge, safety valve, sight glass, steam valves, and ceramic burner. They are hydraulically pressure tested to 120psi. The safety valve opens at 70psi. We'll use it at 25-30psi.

The fuel tank is also from MaccSteam. I used the 2" diameter version. They are filled from small disposable tanks of butane/propane camping fuel.

Never use pure propane. The pressure is too high & the fuel tanks aren't rated for it.

Lastly, two Regner 40451 Piccolo steam engines. These are two cylinder, double action, 10mm diameter bore, reversible, self starting, oscillating steam engines.

Double action means steam pressure is used to both push a piston up and down. In oscillator engines the cylinders swivel back & forth around a pivot point as the crank rotates. The swinging motion opens & closes the intake/exhaust ports -- simple & effective.

Step 4: Major Elements: Radio Control

What fun would life be without radio control?!

To control the turret tank you'll need a radio with 5 channels minimum. There are two engines, whistle, turret rotation & gun elevation to manage.

However, I also added head/tail lights and simulated gun firing with motion, light & sound. My old 6 channel 2.4GHz Spektrum DX6 ran out of knobs to handle everything, so I designed a small controller board to help.

The r/c receiver connects to the controller, which in turn drives the servos, lights, solenoid, etc... This one is long enough as is, so I've detailed the controller board & software in my R/C Controller Instructable. I've including the design files here though: Eagle schematics, Gerbers, source code & hex files.

The 2.4Ghz DSM/DSM2/DSMX r/c stuff is great, and uses encoded transmissions to avoid interfering with other peoples radios.

Alright... onto the build!

Step 5: Chassis Disassembly

My King Tiger chassis was already assembled, so I spent a fun few minutes disassembling it.

Most everything from the chassis needs removing, including the gearbox. Don't remove the suspension though. We need to squeeze a largish boiler, two steam engines, and a fuel tank in there.

Remove a few screws & peel off anything held with double-side sticky tape. Use a screwdriver to lever off the latter. Clean off any remaining sticky gunk. Keep the extra bits & screws in a box. Never know when those will be useful!

To get the gear box out, remove the mounting screws & drive wheels (secured with allen screws). Spreading the chassis slightly can help.

Step 6: Gearbox Modification

To make room for the steam engines & fuel tank, the original gearbox clutch & lever assembly plus electric motor must be removed.

Undo the screws holding the lever assembly to disconnect it. Pull out the transfer axles after loosening the allen screws in the pinion gears & collars. Unscrew the electric motor, and remove the long stiffener screws.

Don't lose the pinion gears from the gearbox!

The rear of the gearbox must also be cut off (see pictures). I tried squeezing in the fuel tank & gears but there simply isn't enough space. Don't throw out the cutoff though. It can be patched back should you ever want to use the gearbox for something else.

Now take two 56 tooth Meccano gears & 1" axles. Attach the gearbox pinions (in their original locations) to the axles. Connect the Meccano gears to the other side including some washers.

Finally, reinstall the gearbox into the chassis.

Step 7: Engine Modification

The tank design has the engine intake ports towards the center, and exhaust ports on the outside.

Oscillator engine intake/exhaust ports are symmetrical, and steam can enter from either side. However, the Regner ports are positioned vertically at different heights. So I rebuilt one engine to mirror image the other.

The two cylinders are held together with springs. Squeeze the cylinders together tightly, and remove the two spring tensioning screws from the rear cylinder with the Regner provided hex socket driver. Keep a good grip on the tool, so you have control when the screws comes loose. Remove the rear cylinder & unhook the front cylinder from the frame.

Now remove the four screws holding the bottom of the frame. Lift vertically, flip it around, reinstall & replace the screws. Replace the front & rear cylinders. Ensure both hook onto their pivot pins.

Insert a tensioning screw into the hex driver. Hold the two cylinders together again tightly, and pickup the loose spring-end with the screw. Insert and tighten into the rear cylinder. Repeat for opposite side without letting go of the cylinders.

Make sure all the screws are firmly tightened.

Step 8: Engine Mount

The engine mount holds the two engines & attaches to the chassis.

Place a 4" x 6" piece of 0.064" (1/16") aluminum over the suspension brackets, and mark where you want tabs. Cut 1" slots with a hacksaw or jigsaw, and bend tabs as shown.

The tabs should be ~1/2" deep. Verify they fit between the suspension springs. Adjust/trim as necessary (pliers, file, etc...)

Use a center punch to mark each tab, and drill through the bracket and chassis. Use sheet metal screws to attach the bracket from below. The drill hole should be slightly smaller than your screw size. For example, a #10-32 metal screw needs a 5/32" hole.

Final positioning of the engines must wait until the reduction gears are in place. For now just place the engines loosely, but go ahead & install the 15 tooth gears.

Step 9: Reduction Gears

The reduction gears route engine power around the fuel tank and help increase torque.

Mounting brackets for the gear axles are made from 13 hole Meccano strips. Bend the ends so they fit within the chassis as shown. Lay strips across the chassis to mark, then clamp in your vise. Use a square to keep the strips vertical. Bend one end on the second hole, the other end on the third. Square up the bend with a hammer.

Take two Meccano axles and cut to ~3.25" in length. Insert into brackets, add washers, then attach 19 tooth & 38 tooth gears. Once assembled the brackets in my tank are 2 1/8" apart.

Fit the reduction gear brackets into chassis so the 19t gears mesh with the 56t gears on the gearbox. The axles holding the 56t gears (and original gearbox pinions) should slip into the Meccano bracket.

Mark position in the chassis side & drill holes.

Secure the brackets with screws. I used 1/4" long #6-32 Phillips flat head machine screws, and carefully drilled a countersink in the chassis outside to keep them flush. Any thick screw head easily conflicts with the tracks.

I used nuts with locking washers, and a small dab of Loctite to keep things tight. The tabs with two holes prevent the brackets from rotating & binding the axles.

Position the engines to engage the reduction gears. Verify you can jiggle the reduction gear transfer axles slightly both side-to-side and length wise. If not, things are too tight.

Mark through the engine mounting holes & drill mounting holes in the engine bracket. Secure the engines in place with sheet metal screws.

Step 10: Mounting Fuel Tank

To mount the fuel tank, you can attach it directly to the gearbox frame or make a bracket.

In either approach, make sure the fuel tank doesn't touch the axles holding the 56 tooth gears. If it does, move or raise the fuel tank until you have clearance, using standoffs, washers, custom bracket, etc...

Direct Mount

For direct mounting, you must drill holes in the chassis for screwdriver access.

Put a dab of white glue on the bottom of the fuel tank mounting lugs. Position the tank between the reduction gear brackets. Remove the tank & transferred glue should mark your drill location.

Verify the drill marks are clear of the tank suspension.

Center punch & drill 5/32" holes through the gearbox bracket & chassis. Now drill 5/16" holes from the bottom -only- through the chassis. The larger holes should fit #6-32 machine screw heads.

Alternative Bracket

I goofed while drilling the direct mount holes & pushed 5/16" through my gearbox frame. Argh!!!

So... a bracket. Take a 2" x 2" piece of 0.062 aluminum. Place where the fuel tank should go & slide forward. Repeat the glue marking trick from above, and drill 5/32" holes.

Screw the bracket to the fuel tank & position within the chassis. Between the front reduction gears is a small gap. Mark there with the center punch. Drill hole through bracket & gear box frame. Fasten down with sheet metal screw.

Note the bracket takes advantage of my oversized 5/16" holes in the gearbox frame, so you'll need to repeat my senior moment. One advantage is the bracket permits easy removal of the fuel tank from above.

Step 11: Boiler Preparation & Mounting

The boiler comes with an injection check valve (one-way valve) on the side. It's used for pumping water into the boiler, but gets in the way here. Replace it with a 1/4-40tpi plug (UST/straight thread)

For mounting purposes, the boiler has two threaded studs. To clear the suspension and the trailing wheel axle of the tank chassis, the boiler needs lifting by about an inch.

I tried only standoffs but the boiler moved too much -- the thin chassis metal would flex. So I used four 3/4" aluminum standoffs connected to a 2" x 3" piece of 0.064" (1/16") aluminum. The boiler attaches to the plate, and the plate to the chassis. Very stable.

I've wrapped the boiler here in 1/16" ceramic fiber paper for some insulation. The paper is soft & cuts with scissors, hobby knife, etc... The insulation helps the boiler heat up faster & protects fingers.

Installing the paper over the boiler fittings is easy. Press the paper onto the funnel port to get an impression & cut out. Repeat for the steam & safety valves, etc... Cleanup the edges with a hobby knife.

I overlapped the paper over the boiler mounting studs, and added a couple extra layers for a tight fit against the mounting plate.

The King Tiger suspension might need adjusting to accommodate the boilers weight. If so, remove the steel suspension strips. Add some twist using pliers & vise, then reinstall.

Step 12: Fuel Pipe

Time to connect the fuel tank to the boiler.

You need about two feet of 1/8" diameter copper tube. Anneal the copper (heat cherry red then let cool) to make bending easier.

All I had (at the time) was one foot lengths of 1/8" K&S copper tube (0.014" wall thickness), so I soldered two segments with a piece of 5/32" K&S tube as a coupler.

Fitting the pipe required some trial & error. Be gentle with your bends to avoid crimping the pipe. I recommend using a pipe bender. Trim the ends to length using a Dremel, hacksaw, or needle file.

Slide on 1/4-40tpi union nuts, and silver solder 1/8" union cones on either end. It's best to follow that order. Forgetting the union nut until -after- you've soldered the cone is... unfortunate and annoying.

Before soldering carefully clean/polish the copper joints with 800 grit sandpaper. Add a drop of liquid flux on the cleaned copper, then fit the brass cone.

Heat the cone - not the copper - with a torch and touch solder to the cone edge periodically until it runs cleanly around. Remove heat & allow to cool. Clean off the residual flux. Verify solder didn't get inside and block the tube.

Inspect the solder joints carefully & make sure they are solid all the way around. If suspect, add another drop of flux. Heat & reflow the solder. These joints are important.

Step 13: Steam Manifold

Steam from the boiler needs to reach the engines, whistle & displacement lubricator. So I fabricated a manifold from brass.

I used a small lathe for this portion. However, you could use a drill press & hand tools if careful. A drill press is important for keeping holes straight & controlling depth. Wear safety glasses & never hold a work piece by hand.

Start with 5/8" square brass rod & cut a 3/8" thick piece. Clean up the faces, and round the corners if you like.

Drill #1 (0.228") holes into centers of two sides & one face. Go about halfway through so they join up inside. The side holes connect to the boiler & steam whistle and are 1/4-40tpi tapped. The face connects to a 1" long 5/16" diameter brass tube.

The manifold tube is made from solid brass rod, and drilled 5/32" through the center. One end is #1 (0.228") drilled halfway deep for the displacement lubricator and 1/4-40tpi tapped. Turn the opposite end down to ~0.227 diameter so it fits snugly into the brass square.

Drill two #38 (0.1") holes for the engine feed pipes, about 5/8" along the manifold tube. Space the holes ~75 degrees apart and 6-32tpi tapped.

Take two brass standoffs with 6-32 threads & drill through (5/64"). Trim the standoff body to 1/8" length, and threads to just barely grab -- don't want the standoff threads going too far into the brass tube. The threaded standoffs make soldering the copper tubes easier later on.

Finally, the standoffs, brass tube & brass square are all silver soldered together.

btw, the purpose of the stepped bore through the brass tube is to minimize steam oil getting into the whistle. A spluttering mess that.

Step 14: Steam Pipes

Engine Pipes

Cut two 2" pieces of 3mm copper tube & anneal them.

The 3mm copper didn't fit my tools, so I made a bending form. The form is simply a 3mm square groove cut into 5/8" round brass rod.

Initially bend the copper tube halfway along, aiming for ~55 degree angle. If using a form like mine, push the form onto the tube halfway down. Now use your thumbs to press it around into shape. The groove prevents kinking.

Install the M5 union nut & solder the 3mm union cones onto each tube. The union nuts & cones come with the Regner engines.

Connect the tubes to the engines with the union nuts. Finish shaping the tubes to fit into manifold. Try to not bend the copper too much since it quickly work hardens.

Once ready detach the tubes from the engines. Clean the copper, add flux & solder them to the manifold. Heat the standoffs not the copper, since heat attracts solder. The standoffs are held by their threads so no worries about them coming loose.

Install 1/2" long 1/4-40tpi pipe nipples into the brass square. Screw on the steam whistle & displacement lubricator. Use drops of Loctite on all threads. The displacement lubricator works by letting condensed steam sink & displace oil. The oil runs into the cylinders reducing engine wear.

Attach the manifold assembly to the engines & finish any minor tube positioning tweaks.

Boiler Pipe

For the boiler feed pipe use 5/32" copper tube.

Measure the distance between the boiler steam valve & manifold. Add an inch & cut the copper tube to length. Anneal the copper & bend ends 90 degrees aiming for 1/2" lengths. Test fit & trim as needed for a good fit.

Install 1/4-40tpi union nuts & solder 5/32" union cones.


To insulate the steam pipes & manifold, I wrapped them with zinc core candle wick. The ends were secured with drops of cyanoacrylate glue. I painted the wick black, to match the color of the body work.

Steam distribution is ready!

Step 15: Servo Mounting Bracket

The servo mount bracket holds the engine servos, whistle servo, R/C receiver/controller, and battery pack.

It's made from 0.032" aluminum and has stiffening flanges bent on all four sides. A pocket for the receiver is formed with a couple more bends. Most bends were made using a vise, block of wood & hammer. A Sheet Metal Hand Seamer is helpful also.

Drill pilot holes for the servo openings & metal nibbler to finish the shape. I removed the larger center using an adjustable 6" mini hacksaw. It allows fitting blades at different angles - not all hacksaws do. Drill 1/4" pilot holes, fit the blade through & reassemble the hacksaw. Carefully cut out the shape. File clean the rough edges.

Install the servos & mark drill holes. Remove servos, punch the marks & drill 1/16" mounting holes. Reinstall the servos and secure with screws.

The receiver & controller slip into the pocket. Pieces of cut-open 3/8" shrink tube & electrical tape insulate the electronics where necessary. The battery sits on the front of the bracket held by double-side sticky tape.

A power switch is attached to an small L bracket JB-Welded to a corner. The battery connects to the switch, the switch to the receiver/controller.

To install the servo bracket, drill holes from the chassis side and into the bracket. Take care not to drill into the receiver pocket, or a servo. :-)

Hookup the servos to the engines using rc ball linkages and the tank is ready to test!

Step 16: Whistle Control

A simple triangle of aluminum redirects whistle servo motion. The corner is anchored to the chassis. When the servo tugs horizontally, the other corner moves vertically.

A piece of brass chain connects the triangle and the whistle. The chain should not be too loose to avoid touching the nearby engine.

Some 1/16" brass rod is used as the servo control rod, with s-curves bent on both ends.

To mount to the chassis, I used a 3/16" standoff, a couple washers & sleeve for tightening the nut against while letting the bracket turn freely.

Step 17: Heat Shield & Lower Body Panels

To finish up the base chassis, we need a heat shield and front/rear body panels.

The heat shield fits between the boiler & engines, and mostly prevents oil from reaching the boiler & smoking. It's a 4" high aluminum plate with curved top plus side and bottom flanges. The curve follows the boiler then angles down to the chassis sides. A gap in the bottom is for the fuel pipe. On the boiler side is glued a piece of the ceramic fiber paper. Sheet metal screws through the chassis on either side secure it.

The front panel covers the gearbox & is a simple 4-5/8" x 2" rectangle of 0.064" aluminum cut to fit. It sits loose in gaps made by the front plastic mounting points. The top corners might need shaving, depending on how the upper body work ends up fitting (visible on mine above).

The rear panel fills the gap between the boiler and chassis, thus its shape is more complex. It angles up from the chassis bottom following the chassis contour, then back towards the chassis top/flange. The boiler curve is transferred on & cut away. I traced the boiler by eye using a ruler, then cut using scissors/shears/metal-nibbler. Took a few test fits. Three holes are drilled through the chassis from below & the panel secured with sheet metal screws.

Step 18: Body Rear

I based the look on Crabfu's steam lobster tank here.

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.

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 on your boilers fixture locations. To preserve the "lobster" look I made sure to keep the top-most lobster shell "points".

Step 19: Body Front

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 a while to flesh out. Lots of prototyping with paper, cardboard & tape. ie: cutting, bending, taping a little back on, repeat, etc... Sketches show 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.


High temperature engine enamel was used to paint the body. The aluminum is sanded, washed & scrubbed with soap & water (removing oils), rinsed thoroughly, dried, then primer applied immediately. Paint doesn't stick to aluminum well, so sanding provides a mechanical bond. Once the primer dried, the rear was painted with multiple coats of semi-gloss black & the front a metallic burnt copper orange.


I found some metal King Tiger tank accessories on eBay (shovel, hammer, etc..). These were painted, mounting holes drilled & then JB-Welded onto the body.

Ring Gear

After the paint fully dries, a 3.5" diameter Meccano ring gear (133T/95T, part M180) was attached to the u-shape panel covering the fuel tank. I used Philips flat head machine screws with drill holes countersunk into the gear ring. It's important the ring gear surface be fairly smooth for the turret to sit properly.

Step 20: Body Fenders

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.

Step 21: Condensate Tanks

The condensate tanks are optional. They capture liquid water & oil from the engines. Especially the latter. Expelled steam oil from the engine quickly makes a mess of a driveway/patio/etc... If you are not worried, then just route exhaust pipes to the rear of the chassis.

The tanks can be made any number of ways. For example, copper plumbing fixtures. Two end-caps & a coupler for 1" pipe with bits of pipe inside. Cleanup the joints so they fit tightly, solder it up & you've a tank.

Brass Pipe

I used 1-1/4" brass pipe, and turned four 0.08" thick end-caps from 1-1/4" solid brass bar on the lathe. The pipe sections are 3-1/4" long. The end-caps were made using a cutoff tool. A shallow cut to match the 1.17" inner diameter of the pipe, and then cutoff.

A #1 hole drilled in the top is for the vertical exhaust, and a 5/32" in the front end-cap for the engine pipe

The pieces are cleaned, then a ring of thin (unmelted) solder is placed within the joint. Apply heat & once the solder melts, push end-cap fully into place. Repeat for other end-cap's.

Two studs from 3/8" brass rod are drilled & 4-40tpi tapped, then attached onto the bottom. These can be JB-Welded after suitably scratching the brass surfaces for adhesion though soldering is better.

Condensate Exhaust Vent

The vertical exhaust pipe is a simple 3/4" length of 1/4" diameter brass tube. I used a 1/4-40 TPI die to thread the pipe & tapped the tank. Alternatively you could buy a 1-1/2" pipe nipple and cut it in half.

Engine Exhaust Pipes

3mm exhaust pipes from the engines need a simple 90 degree bend to feed into the condensation tanks. The oversize 5/32" holes in the tanks make it easier to install/remove the pipes. Pipes get wrapped in candle wick like the steam feed pipes.

Step 22: Turret Base

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 (for mounting in the lathe). A #1 hole was drilled about halfway to fit on the servo spline gear.

1/8" thick aluminum bars are JB-Weld glued onto the idler gear tabs to thicken them. Holes are drilled & two 3/16" standoffs per tab fitted. Fit a 1/8" diameter sleeve over the expose thread, a 1/16" slice from a 10T Meccano gear over the sleeve, and then nut to secure everything. The nut tightens against the sleeve & the gear spins freely.

Aluminum servo mounts (5/8" L x 1/4" W x 3/16" H for my servo) were marked, drilled & 2-56tpi tapped. Screw mounts onto servo, then position servo with the base sitting on the ring gear. JB-Weld to the base.

Note: JB-Weld doesn't stick well to smooth aluminum, so thoroughly scratch up the contact points first.

Step 23: Turret Body

The turret body started simple (a cylinder), and became less so... I didn’t like the look so added the curved gun port bump-out (see drawing) & 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.

Step 24: Turret Gun

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. Its 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!


One end of the smaller tube is plugged. The plug connects a 1.5" piece of 1/8" steel rod to the smaller tube. Make sure a magnet can stick to the rod. Drill a shallow 1/16" hole into one end & 2-56tpi tap. JB-Weld the tube, plug & rod.

I custom fabricated a 1" solenoid on the lathe, forming the bobbin from 3/8" diameter Acetal plastic rod.

It proved very bendy, so first a 5/32" hole was drilled through the center, then a steel rod inserted. Next a 7/8" long center section was turned down forming the bobbin. Shellac coated wire is tightly wound onto the bobbin & wrapped with tape.

Slide the steel rod of the smaller tube assembly through a weak spring & into the solenoid core. A 1/2" long brass screw (2-56) w/washer fitted into the other end threads into the steel rod. When the solenoid is energized, it retracts the aluminum tube. When released, the spring pushes the tube back out.

The smaller tube also contains an ultra-bright yellow LED. I doubled up the LED wiring to reduce barrel twisting & binding.

The gun is inserted into the mount & fitted with a 1" Meccano axle. A couple Meccano collars holds it in place.

Step 25: Turret Solenoid Driver

The solenoid proved annoying since it dropped the battery voltage enough to brownout/reset/disconnect the r/c receiver & controller logic.

Time for a capacitor & something to limit charging current. When triggered, the capacitor dumps its charge into the solenoid without overtaxing the battery.

I used three 1F 2.5V supercaps in series with a current mirror to charge them. A simple 50 ohm series resistor would work also, but the recharge time is longer. Note supercaps are easily damaged, so there is some protection circuitry. The protection prevents over-voltages when charging & negative voltages during discharge.

The white goop is silicon to keep the supercaps from moving. The driver is wrapped in cut-open shrink wrap tube & electrical tape.

No more brownouts!

Step 26: R/C Details

I find the Spektrum DX6 a headache to setup for different models. Instead I tuned the tank to the transmitter. Two Microchip PIC 16LF1825's based controllers are used. One in the base attached to the receiver, another in the turret.

For some transmitter actions, the controllers range limit the servos (engines & whistle), other actions are converted to delta adjustments (turret rotation & gun elevation), and others into lighting on/off toggles.

The base controller also sends r/c receiver signals to the turret over a serial bitstream. Thus only three wires are needed: power, ground, signal.

With the Transmitter Right-Switch off,

  Left-Switch = Whistle (range scaled & limited)
  Left Vertical = Left Engine (range scaled & limited)
  Right Vertical = Right Engine (range scaled & limited)
  Left Horizontal = Delta adjusted Turret Rotation
  Right Horizontal = Delta adjusted Gun Elevation

With the Transmitter Right-Switch on,

  Left Vertical Up = Toggle headlights.
  Left Vertical Down = Toggle tail lights.
  Right Vertical Up = Toggle turret internal “map” light.
  Right Vertical Down = Fire gun (pulse solenoid, led, trigger sound driver).
  Left Horizontal = nothing
  Right Horizontal = nothing

I’ll cover the design & programming of the controllers in more detail in my R/C Controller Instructable.

Step 27: Running the Turret Tank


Never ignite the burner or run the tank indoors. Take it outside.

Always wear safety glasses. The boiler can flare during burner ignition. Things -can- break and go flying.

Note the cylinder cap on one of my engines is bolted down. It popped off during a run. Heck of a surprise & a pain to repair. It'd be a far bigger pain though should someone get hurt. So ALWAYS wear safety glasses & keep a fire extinguisher handy.


Open top and bottom of displacement lubricator. Put a rag underneath to catch any draining water. Close bottom port & add steam oil. Tighten top port.

Add drops of normal engine oil to steam engine lubrication cups. Make sure engines can turn freely & aren't stuck from dried oil/etc...

Remove turret. Verify fuel tank valve closed off, and union nuts on fuel tank & burner are tight. Fill tank with propane/butane camping fuel.

Boil some distilled water. Avoid "purified" or tap water because minerals will foul the boiler sight glass. There is some argument from people about what is best. Pure distilled water can be slightly corrosive. Therefore some suggest adding a -small- amount of tap water to the distilled. Some people prefer rain water.

Remove boiler safety valve & use small funnel to fill boiler with boiled water until sight glass 1/4" from full. Replace safety valve & tighten.

Starting Burner

Here we go! Ignite a utility lighter. Matches aren't a good idea here.

Open the fuel tank valve & touch the lighter to the boiler funnel. If the lighter goes out, or boiler doesn't ignite immediately, close the fuel valve. Wait for the fuel gas to dissipate before retrying.

The burner should ignite with a pop, followed by a steady quiet roar. It takes several minutes for the boiler to reach pressure. Reinstall the turret, turn on the r/c transmitter, then the tank power switch.

Once the pressure gauge reaches 25 to 30 psi, open the boiler steam valve & have fun!

Check the boiler sight glass periodically. When the water level touches bottom, turn off the fuel gas.


Open the boiler blow down valve below the sight glass & allow pressure out from the boiler.

Remove the safety valve. Remove turret & turn tank over to finish draining. Do this while the boiler is still hot if possible. Leave the safety valve off so remaining water can evaporate. Never leave standing water in the boiler.

Drain the exhaust condensation tanks. Use syringe if needed.

Clean up any water & oil around the engines.

Live steam is messy, but so much fun!

Step 28: Demo Movie

A second run of the turret tank. This one includes climbing an obstacle, showing off the whistle, etc.. Don't miss the video included on the Intro page also!


Epilog Challenge VI

Runner Up in the
Epilog Challenge VI

Tech Contest

Runner Up in the
Tech Contest

Remote Control Contest

Participated in the
Remote Control Contest