Going Gas Powered

Well, here goes. Taking the tank apart, pulling the electric motors, and swapping in a gas engine with a idler engaged pulley style transmission.  I’m tired of the 1hp from the electric motors, and not being able to have the tank really drive anywhere fun. Will probably go with a 3 to 6 hp engine in the back, and transmission in the front.


Here’s the basic plan for the transmission.  The motor spins 2 shafts in opposite directions.  Each has a pully on each side, which can be engaged with an idler, giving the 4 options:  Left Forward, Left Reverse, Right Forward, Right Reverse.

To turn the 2 shafts in opposite directions, the current plan is to have the chain wrap around a sprocket on each shaft, and an idler to give the proper clearance.
The other option is to drive one shaft with the motor, and have it drive the other shaft in reverse via cogs/gears.  But I’m leaning toward the chain method.

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.

Pulleys in place

I made the hubs that connect the pulleys to the drive sprockets.  I used a 3″ washer, a piece of steel tube, and a floor flange which matches the bolt pattern on the sprockets.

Then I bolted the hubs to the drive sprockets, and the pulleys to the hubs.  I fitted a test-belt (taped together) to figure out the length of the belts I need.  Everything lines up great, lookin good.  Now time to take everything apart to work on the lower hull, more to come on that soon…

Making bogey mounts

Before I can have a rolling chassis, I  need to make the frame mounts for the 3 bolts that attach the bogies to the frame.

Here are the mount  pieces:

They will be welded to the frame like this:

Bolting the bogies on, to hold the mount pieces in place while I weld them on:

Here they are, all of one side bolted on, ready to be welded… they really make this chassis start to look like something.

Once the mounts are all welded in place, I will remove the bogies, add the spacers, bogey arms, springs, upper rollers (which support the track), and finally the wheels.  I am currently using 1/4″ bolts.. I’m a little worried they will be weak, so I might drill them out and replace them with 3/8″ or even 1/2″ bolts.  I could also just replace the bottom center bolt making it the load bearing bolt.  We shall see.

One other note… the wood hull will also need to have these same holes drilled, so the bogies can mount on the outside of the hull.

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: