A quickie...

Had a few extra moments today to play in the garage. Started work on the drive sprockets. The base is just a cone. To that cone a ring will be welded on each end. The actual sprockets will then be bolted to the rings.

Brummbär Progress Video Log

The Brummbär begins.

First off, a little of the back story.

This build is intended from the beginning to be a PAV (paintball armored vehicle) for use in paintball/airsoft games. It is intended to have a minimum crew of 2, though I am trying my best to cram three in the thing.

The Brummbär was selected as the model for this build for several reasons. First of all, construction is pretty straight forward and in line with my skill level. Second, it has a very high profile (unlike the Hetzer) making it easier it fit in the thing. Third, it has a big gun. What I mean by that is the original had a 150mm main gun with a short barrel. This gives me a lot of options for designing a scale version. And fourth, it is casemate (turretless) design. Though not having a turret will be a slight hindrance on the paintball field, it is safer without one. I have several ideas to make a turreted design safer, but that will have to wait for future projects.

This project will progress a little differently than the last one. The first items on the "to do" list is suspension, drive sprockets, road wheels, rear idlers, return rollers and tracks. After all of that is done, I will then start tackling the frame/hull and what not. Since this project will be much heavier than the Hetzer project, it is important to have all the suspension and tracks ready to put on the hull as soon as it is done so the lower hull can be moved around. How heavy do you ask? It is my goal to keep the finished tank under 5000 lbs.

I have had a couple days so far working on the Brummbär. So far, it is not very exciting. Just cutting up the little pieces that will get put together for the suspension. Progess has been slow as I am still learning how to effectively use my plasma cutter. I also had an issue with my circle cutting jig not fitting the torch of my plasma cutter. Everything was correct, except for some reason the diameter of my torch head was about 1mm too big. Just enough to keep it from sliding into the jig like is suppose to. I fixed that problem by carefully sanding the torch head.

First picture is some of the small pieces I chopped up last week.

The next is of some discs that I cut out. These ultimately will become the road wheels. 20 down, 16 to go. 

One other item of note: I have started a video log for the project. It can be seen on YouTube here:

Brummbär Progress Video Log 04-12-14

First video I have taken with my phone. Audio went in and out a little. I will try and correct that in future videos.

Every ending is a new beginging.

Everything in life does not end the way we thought it would. This is very true where my Hetzer is concerned. An ambitious project to be certain, but achievable. However, it will not come to fruition. My biggest mistake with the Hetzer was not fully articulating the projects goals. I said early on that I had no idea what I was going to use it for, I just wanted to build the thing. As I continued to work on the project, I began to realize I had some serious design flaws. No not in a mechanical sense, but in the capabilities of the finished project. It simply was not enough to just build it; I wanted it to be able to do more than it was designed for.

Specifically, I wanted it big enough for more than one person to fit in the thing. The Hetzer, even at full size, is not very big; knock it down to 60% and one person is all that is going to fit in comfortably. This "problem" is made worse by the fact there simply is no way to make it bigger without re-doing everything. So, several months ago I made the decision to scrap this project and start another. I used the winter hiatus (read: cold weather) to chose a new tank and work up the CAD drawings for it. I also made several key upgrades in my little tank factories capabilities. In the Hetzer project, I tried to use as many parts as possible "off the shelf" due to my limited fabrication skills/equipment. This made me make many compromises in how close to scale I was staying. I added a plasma cutter, metal bending equipment and a new welder to the arsenal. Moving forward, I will fabricate almost everything from scratch. Outside the engine/hydraulics package, about the only thing I am not making myself is the bearings and nuts & bolts.

So , last week the Hetzer was cut up for parts. I salvaged the longer pieces of square tub and will use the springs and bearings in the next project. The hubs, rims and wheels will be sold or traded away.

So what is the next project you ask?

The Brummbär......

Finishing the main frame and axles.

After the suspension was completed, I completed the main framework. There will still be additions to it for support of various item and attachments, but for the most part the frame is complete.

The primer is weld thru, so I do not have to clean it off before welding an area again. So far, with the exception of the framework, most parts have been "off the shelf" items. The front drive sprocket axle will be made from 1018 1" round bar with pillow block bearings providing the support. The hubs are go kart live axle drive hubs and the rims are for a trailer. 

The rear idler was a little more of a challenge. The hubs and rims are for a trailer. The swing arm is custom made. The spindle is welded in on one end and the swing arms axle is on the other. The whole assembly is supported by two pillow block bearings. Not completed yet is the attachment point on the swing arm axle for a turn buckle. The turn buckle will be used to move and secure the rear idler thereby adjusting track tension. There is some additional support framework needed as well.

Progress so far has been fairly swift and I am significantly ahead of scedule. Next up will be the tracks and sprockets. I have taken most of the winter off from the project. It has been very cold this winter and I just didn't feel like paying out in the cold. :)

Spring is fast apporaching and I am preparing to upgrade/add several items in the garage that will significantly improve/increase my metal fabrication skills. I will no longer be dependant on "off the shelf" items to use for my parts. Till the next time I will give you a look at the full progress. This picture was taken on 09/22/13.

Trying to Grow Legs

One of the most important pieces to the puzzle is the suspension and road wheels. Everything is riding on them, literally. Early on I made the decision to use as many parts "off the shelf" as possible. The trick is to know what is usable/economical and what is not. My plan is to use a 20" cart wheel as the base for the road wheels. My intention was to fashion a hub cap to go over them to give them a solid appearance. In reality, I am going to need to fill in the spokes (at least partially) to stiffen up the rubber thread in addition to the "hub cap". Hindsight is that I would have less time and money involved in making them from scratch then modifying an existing wheel. One other thing that was disappointing is the size. Officially listed as a 20" wheel; however, it actually is 18.5" in diameter.

Of course the wheels are only as good as the suspension they are attached to. Luckily for me, the Hetzer's suspension is very straight forward and no frills. The road wheel swing arms are in pairs facing away from each other. On top of the road wheel swing arm, directly above the road wheel spindle, rests one end of an elliptical leaf spring. The spring is anchored to the hull in between the road wheel swing arms and can pivot.

While this setup is not nearly as clean cut as a torsion bar; it is something that I am able to fabricate without having to get assistance from a machine shop. I basically took the original design and scaled it down and modified it with over the counter parts.

An interesting aspect of my design is the spring resting on the swing arm past the road wheel spindle. This will add mechanical advantage to the spring thereby "stiffening" it. This allowed my to use a smaller less expensive spring.

Counting Rivets

I'm afraid I'm a bit of a tank snob. By that I mean when a tank is used in a movie or such, that it be correct in detail. Some of the more notorious examples are movies like Patton and Battle of the Bulge. Kelly's Heroes and Saving Private Ryan did a better job, but still wrong. Of the major productions, Band of Brothers probably does the best job.

In Patton, none of the vehicles are of period and the Germans are driving around in American M-48 tanks, ironically enough known as the "Patton".

In Battle of the Bulge, again no period vehicle were used. The Germans are again riding around in American equipment with the feared Tiger II being portrayed by a M-47.

Movies started to get better though. The Tiger I tanks used in Kelly's Heroes are mock ups based on Russian T-34s. While it is certainly better than the previous two movies, still not quite there though.

Saving Private Ryan does a much better job with equipment in general and vehicles specifically. Most are of period and authentic. However, at the climax of the movie, the battle "hinges" around two Tiger Is. These are T-34 mock-ups like in Kelly's Heroes. It would be easier to forgive if so much of the action did not pivot around the suspension, road wheels and tracks. Of course, these are the things that look the worst on the mock-ups.

Band of Brothers continued the advancement of the movie industries accurate portrayal of the period. Most equipment and vehicles are authentic. The mock-ups are done well. Their visual weakness are usually obscured with scenery or the action sequences. The Jagdpanther below is a mocked-up Russian T-55. It is fairly well done. Of course, there is no hiding the fact that a T-55 drive sprocket is in the rear while a Jagdpanther's is in the front.

However, there is a silver lining. In the upcoming movie Fury (November 2014), permission was granted by the Bovington Tank Museum to use the only fully operational Tiger I in existence (Tiger #131) in the movie. Hopefully, if they have gone through the trouble of getting Bovington to agree to let them use their tank (they have refused everyone else) in the movie, then that attention to detail will carry over into the rest of the film.

Now what does this have to do with my little Hetzer? Well I wanted you to understand the depth of my snobbery, especially when it comes to the suspension, road wheels and tracks. I anticipate I will spend as much time and effort on these three items as everything else combined.

Breaking Ground

After many weeks of research and planning, I was itching to start building the bloody thing. The lower hull went together easy enough. The challenge here was learning how to weld. My first attempts were; well, very poor. I am using an inexpensive flux core MIG welder. Not the best out there, but certainly capable of producing decent welds. When my skills get better, I plan on getting a more capable welder. Until that time, the funds have better uses.

Everything went together fairly easy. Welding was easier then I feared it would be. Mind you, the welds look atrocious, but they are strong. During this stage I was spending three times the amount of time cleaning up the welds as I was in actually welding.

With the basic part of the the lower hull frame complete, my plans were to work on the suspension. Welding at ideal angles is challenging enough. Throw in odd angles or upside down and it becomes a real bugger. At this stage the frame can easily be moved, turned or flipped however I need it.