Controls and wiring

Well I got the switches in the control box wired, the levers installed, and the whole system all wired ready for testing.  I have a loose wire or the pass-through relays are acting funny, so it is working intermittently, so I am trying to track down the culprit.


I also installed the tracks and the drive belts.  While the electronics were working, I tightened them up, to see if the thing would roll!  And… drumroll…..  the belts slipped on the pulleys.  This is either because the pulleys are too slick being made of UHMW, or the belts just aren’t tight enough.  I will first try to just add some idler pulleys to tighten the belts, and hope that works.

Also, the total weight of everything seen, including suspension, tracks, and batteries, is 240 lbs, which I am pretty happy with.  The batteries are probably a good chunk of that weight, but that is how it works with electric vehicles.  Batteries are heavy, or expensive, one of the two.

Track adjusters, rollers, etc

I buttoned up some of the detail work for having the tracks on and all dialed in.  I made the return rollers (the white wheels that keep the track from hanging down, or bouncing around and hitting the bogies:



I also finished and installed the rear idler adjustment components.  Welded the bracket onto the frame, and installed the arm and turnbuckle.. so shortening the turnbuckle tightens the track.  Need to do a few finish/cleanup welds on the brackets, but the adjusters work perfect for tightening the track, which is great.


Now I will be moving, so had to pack up the tank for a little bit, but will hopefully be working on some other stuff in the meantime, like getting the motors and working on the controls, etc.

Some eye candy..

I installed the finished tracks and wheels.  They look good.  Note that I didn’t put the bolt in to connect the ends, as I am currently working on the rear idler for adjusting track tightness.



Here you can see the nice meshing of the the drive sprocket and the track:


Diggin in to work on the cleats

First, I made a bunch of 1-3/4″ x 6″  pieces of 3/8″ UHMW.    Then I setup a guide on the table saw to cut all the corners off.

I made a template for the cleats out of plywood and aluminum diamond plate,  which I then used to cut the other area out with the router (flush bit).  This yields a nice cleat, with pre-marked holes (where I will countersink a screw to attach them to the treads).

This isn’t the fastest process, so it will be a few days before all the cleats are finished, and then a few days to attach them all.

Tracks are…. closer to being done.

Ok, so I “finished” the second track.  I still need to do the special hinged treads on the ends.  But nevertheless, a huge step.

I also need to add cleats to each tread.  That will be a decent undertaking, but is fairly crucial.   They serve many purposes, like traction in soft ground, and protecting the tread blocks, etc … but they also reduce surface area friction on pavement.   And of course, they will make the tracks look like the real thing.  Here’s my design/pattern for them:


Track pieces complete, ready for assembly

Here is the finished pile of track guide blocks, each with 2 pilot holes drilled.

Here I made a pattern for the tread spacing for actually assembling the track.  This will keep everything evenly spaced, square, and straight.

This is the jig that will hold the guide blocks in the center while I screw down through them, then through the conveyor belt, and into the tread on the other side:

I of course couldn’t help but set up a section to show what it will look like after I attach everything together:

Tracks, the long road of repetition

So, I first cut some 1/2″ UHMW into strips, then cut those to pieces 7.5″ long.

Then, on each one I made 8 table-saw cuts (2 from each corner).  So far I have done 46 of them.   Turns out I will actually need 59 for each track.

Here I am just setting a few on the belt, as a mockup, to get an idea of how the spacing will look, etc:

And then I am routing down the 2 corners that come in contact with the drive sprocket, for a snug fit:

So slowly but surely making all the track treads.  Once the treads are done, I will make the inner track blocks/guides, and will finally be able to start assembling the tracks.

Rear Idler Assembly

The rear idler wheels are, much like the drive wheels, the ones “in the air”, except in the rear of the tank.   They need to be able to move or pivot to take up any slack in the track.  I have thought about different ways to do this, each with different benefits, and pitfalls.    The easiest would probably be a a sliding axle type of setup, but your hull needs an elongated hole in it, in which water and dirt can enter.

So, I am using the design that Dave Manson uses in his famous 2/5 scale Sherman (his many videos are a youtube sensation, the ultimate tank builder’s HowTo).

His design uses an eccentric shaft, which basically has 2 arms at 90 degrees, with a connecting rod going through the hull.

Looks like this:

I have begun building the idler assemblies, because I need to know where to have a hole in the hull, which effects my frame design, etc etc.

I am just using 8″ long 5/8 bolts for the idler axles.  Some 5/8″ steel rod as the “peg” that goes through the hull and connects to a lever.   The lever, then, when pulled down, pushes the idler wheels back, which tightens the track.   Very elegant solution, thanks again to Dave Mason.

Drive Wheels done. Track time.

Finished the drivewheels.  Still need to get a few more bolts, but 2 works for now. They look pretty much awesome.

So, now that I have those, I can begin working on the tracks, since I can figure out the exact spacing, size, and shape of the overhanging treads, which the drive sprockets will turn.

I cut up a rubber doormat to simulate the rubber track, and made some test plywood treads and inner alignment blocks, which apparently are called “bells”.

I then countersunk some holes for wood screws which go through the tread, through the track, and into the bells.

Then I put it over a drive wheel to test how it rolls, if it catches etc.

It does slightly catch as the track is coming off the sprockets, so when I make the actual treads out of UHMW, I am going to router the corners off the ends of the treads, and round off the corners on the drive sprocket teeth.  Like so:

Bogies and Roller Wheels

Bogies are the sets of roller wheels, which provide the track with its means of suspension.  I have considered a few different designs, including the two below which are loosely based on the M3/M4 Sherman tank.  I think for simplicity I will go with the One Spring design, since often times simple is better.

The main difference between the track and bogey system I’m using, versus from an M3/M4 Sherman, is I am using an inside, and an outside row of roller wheels.  These roller wheels will ride around 1 row of blocks on the inside of the track, which will keep the track from coming off.  An M3/M4 uses 2 rows of these alignment blocks, an inside and an outside, with just 1 row of roller wheels between those.     The reason to do it like I am, is having a few extra rolling wheels seems easier than making 2 sets of inner alignment blocks, where you need to do hundreds of them.  There are a few other reasons, but no one really cares.

Still not sure exactly what material to make the bogey pieces out of.  Leaning toward UHMW plastic, or possibly aluminum, trying to keep it fairly light.