Another Sherman Tank (Rev 2 - RC)

This is a 1/20th scale Sherman tank, it is designed to add motors and RC control. Tried to make it look like the late model upgunned versions. I was not trying to create a historically correct model, just a model that would be reasonably fun to put together, look decent, and not send you to the hardware store for more pieces to complete.

Everything needed to assemble is printed with the exception of some fast set epoxy and on this model I used .3X4X10mm springs in the shocks for a more durable suspension. The track and suspension are held together with filament. A couple clamps are nice to keep a couple things aligned as I found plastic parts can warp. The normal print clean-up tools and a 1/4 " round file was good at cleaning up holes to provide smooth rolling.

I used a Tamiya 70168 Double Gearbox based on someones recommendation.  Not super strong but good enough if you clean up the model and get it rolling real smooth.   The gearbox and an L298n motor controller driven by an ESP 8266 was about as cheap as you can get with WIFI and everything needed.  Used sample code for hosting a web page on the controller to provide web based controls fully hosted in the tank.  I can provide the code if desired but likely will need modifications depending on what control processor you use.

PLA+ was fine for all parts with the exception of the tires for the main road wheels, those are tpu and stretch over the pla wheels. While the model is fairly large the parts are sized to fit on a normal printer I will post a split hull for that.

Part List

Drive Axle RC - 2

Drive Axle RC Drive Gear - 2

Drive Axle RC Gear - 2

Drive Module RC Base - 1

Drive Module RC Bracket - 1

Screws to attach RC Bracket to Base - 2

Drive Sprocket Assem  - 2

Drive Track Assem - 12

Frame RC Front - 1

Frame RC Center - 1 

Frame RC Back - 1

Gun Mantlet - 1

Gun - 1

Hatch1 - 1

Hatch2 - 1

HVSS Bracket - 6

HVSS Pivot Axle - 12

HVSS Spring - 12

HVSS Shock Inner - 6

HVSS Shock Outer - 6

.03x4x10mm spring (placed inside outer shock from Compression Springs Assortment Kit)

Plate Back Plate - 1

Plate Back Shelf - 1

Plate Front RC - 1

Plate Front MGP - 1

Plate Front  - MG

Plate Top - 1 

Spacer 1mm - ~40

Spacer 4mm - ~12

Tank Fenders Left - 1

Tank Fenders Right - 1

Tank Fenders LFront Curve - 1

Tank Fenders RFront Curve - 1

Tank Gas Filler - 2

Tank Grate  - 1

Tank Hand Holds1 - 3

Tank Hand Holds2 - 3

Tank Hand Holds3 - 3

Tank Rear Grate  - 1

Tank Yoke - 1

Turret Guard - 1

Turret Hatch Top Lid - 1

Turret - 1

Turret Base - 1

Wheel Idler axle - 2

Wheel Idler - 2

Wheel Idler M6 Nut - 2 (Slice xy at 110% or else it wont thread easily on bolt)

Wheel Lock - 40

Wheel Return Large Axle - 4

Wheel Return Large Wheel - 8

Wheel Return Small Axle - 6

Wheel Return Small Wheel - 6

Wheel Road RC axle - 12

Wheel Road RC Tire -  24

Wheel Road RC Wheel - 24

The nut for the Idler axle should be sliced at 110% on the X and Y axis and 100% on the Z. Freecad does not leave enough relief on the threads if you don't widen it. If you expand the z axis the thread pitch will be off. Also thickening the walls on the nut and axle helps strengthen it.

Post-Printing =============

Glue the 3 frame pieces together. Clamps help hold them together.

Build the gearbox, steel axles must be shortened with a dremel to fit in the frame.  The drive gear fits on the hexagonal axle as pictured.  The smaller RC gear fits over the half axle inside the front frame.  Use spacers to center each side in the pocket inside the front frame.  The Gearbox is mounted in the RC Base and Bracket.  Then RC base is glued to the bottom of the frame with the drive gears engaged to the RC gears on the axle.

Glue the Drive Sprocket Assembly onto the the half axles aligning the end of the axle to the outer edge of the sprocket.

Print and assemble six of the HVSS suspension components as pictured. Your favorite filament will thread the pieces together. If you desire to secure them pinch the ends so they can't slide out.  Each shock on top should slide freely and was enlarged contain one spring to allow the suspension to move freely.  

Add the road wheels to the suspension pieces. Each takes 2 axles, 4 wheels, 4 tires, 4 1mm spacers, and 4 wheel locks. Cleaning up the components and perhaps some dry lube will make sure the suspension and wheels roll cleanly. 1/4" round file for the holes works great.

The suspension modules can be glued to the frame into the locator slots.

Install return wheel axles and road wheels alternating the short small ones with the two larger double rollers. Use spacers to align them.  Pay special attention all wheels and sprockets must align properly so the track runs smooth and does not hit the side of the tank.  1 and 4mm spacers are used for this. The road wheels on the HVSS bracket set the correct distance for all other rollers.

Install Idler with nut. I trimmed one side of the nut for clearance on inner frame. Tighten and glue once you get desired tension after installing track. All the wheels and sprockets use the same wheel lock to secure when you are happy with the alignment.

Join 6 pieces of track with filament per side. That should be the right amount to loop around the wheels at this time and secure with a final piece of filament.

Glue the turret base into the top sheet. Glue the turret guard around the base. If you printed the top sheet in 2 pieces glue together first. The turret should snap in fairly easily once dried. 

The mantlet/gun mount should snap into the turret with some force, I did snip the sharp edges on the turret to widen the entry for the pivot. The barrel should slide in snugly.

Slide the Front plate into slot of the front frame  (I did not glue this).   Top plate can be slid over grooves in the frame.

Glue rear plate to top plate. Use the frame to help hold it while glue sets. Same as above I never glued the rear plate to the frame. So entire top of the tank top can slide off backwards.

Glue side fenders on top plate. Glue front fenders on front plate and drive guard.

At this point I think you are just adding some of the decorate items, tank fillers, hand holds, machine gun barrel, hatches, or whatever you decide to add...

Added the code for simple control example for an ESP8266.

Modified the front end to accommodate a drive module.  Updated the suspension to use steel springs since plastic eventually fatigues and sags.  Added some minor cosmetic changes.  Even if you are not going to do RC this model is a bit easier to assemble and adds a couple of details.