Frame again

Frame coming along nicely, and drivewheels are done…

Clamping second side to completed first side:

Both sides done set out to decide width:

Notice the (soon to be) supports across the bottom of the frame.  The drive sprocket teeth are shaved to a point, and drive wheels are fully assembled (except bearings):

Welding the frame

I am making the frame, and doing a little reshaping of the drive sprockets right now.  The frame is going pretty well.  My plan is to make 1 side, then make the other side on top of the first side, so they are as identical as possible.   Then, I will add the cross-members from one side to the other.

As for the drive sprockets, as mentioned in my last post, I am taking the corners off of them, so the treads clear as they come off.  I am just running the corners of the teeth, freehand, along the straight-cut router bit.  Doesn’t have to be perfect, just a little more clearance.

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:

Drive Sprockets almost done

Ok, I finally made some really good progress on the drive sprockets.   I cut out all 4 (2 for each drive wheel).  I had to spend a little time making a homemade router table for my router, but once I finished that, I was in business.

So, after being cut out, due to the bending of jigsaw blade, they needed some cleanup done on them.   So I put a straight bit on the router, and just used it to shave the jagged edges, like this:

Then I put a chamfering bit on the router, which cuts a diagonal edge.  Before on the right, after on the left:

Here they are, they turned out great.

All I have left to do now, is drill the holes to bolt it to the drive wheels, and drill a 1-3/8″ hole in the center for the bearing to fit it.    Here’s the bearing I’m using:

Also, finished both hubs for the drive wheels, so they are almost done.   Once the drive wheels are finished, that is huge, cause I will be able to start working on the tracks, since I’ll know the exact spacing for the treads on the tracks.

Hull, frame, and a little luck

Sometimes, when building a project  like this, nothing works better than a little luck.

I have figured out the plans for the frame, although I don’t have a set width decided on yet.  And my plan before today’s epiphany was to buy some steel sheet metal for the sides and bottom of the hull, and weld it on, with either some home-done long bends, or really long seam welds.  Which are both totally fine, I can do such a thing.   BUT, if I can have some nice, factory done edges, and not have to pay for the steel, that’s a no brainer right?

Then, I remember I have this thin metal wardrobe closet thingy in my shop.  It currently has my shop rags in it, and it’s totally in the way, in the middle of the floor.    It is about the right height, and about the right depth to flip on it’s back, make some cuts, and weld my frame to the inside of it.   The only problem is it’s too wide, so I will need to taker a strip out of the middle of it, and weld it back together.

I have also decided on the steel for the frame tubing, I got some 3/4″ square tube .065 thickness.

Here’s the basic plan of attack :

Body, turret, and chassis

My plan is to first build the chasis, which will include the tub/hull, drive wheels, tracks, bogies, motors, batteries, electronic controls, etc.  This will be a totally self-contained system.  The tank should drive, and function almost completely with just the chasis in place.    This will come in handy for me to be able to test drive the tank, because I may not fit inside the tank when the body is on.

The chasis should look something like this, although the controls, batteries, motors etc are not shown:

Next,  the body.  The body will fit and bolt onto the chassis.  The body needs to be lightweight, yet sturdy.   This is also what really makes it look like a Sherman Tank.  At this point I’m considering either thin UHMW (1/8″ thick) or plywood.   The UHMW can actually be bent or curved if heated, and will hold that shape.  This feature alone could make it more useful than plywood.  I would probably need to make a sub-frame like structure to attach the panels to, and I’m not sure how to make the seems look good.   I’m still thinking about his, and will try a few small-scale tests with materials, to see which makes the most sense.

Finally, the turret.  This is the big gun, and the round part with a hatch, on top of a tank, that most people are familiar with.  This will attach to the body.   There are still many questions for how I will do this also, like how will the gun shoot, how will it all turn, etc etc.   I’m not too worried at this point, but I am keeping it in mind for now, in case it effects the construction of the other parts, or if I see something that I think could be easily modified to work as the turret, or any of it’s parts.

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.