Twisted

Brummbär Video Log Update

A little more work was done this week. The good news is the road wheel axle hubs are tack welded and ready to go.

The bad news is I broke my ring roller. However, the good news is I broke my ring roller. Probably a blessing in disguise. It rolled some terrible rings. It put a twist in the Z axis. I am in the process of making a ring roller from scratch. I hope to have it done before the coming weekend. I also hope that I can flatten out the remaining 6 or 7 seven rings I rolled with the old roller and then run them through the new one and get the twist out. I hate to throw 20' of flatbar in the recycle bin. :(

I did play around with some of the rings I do have on some extra road wheels. Did not go all that well. The twist in the ring caused all manner of issues. I probably will not try tacking any more until the ring issue is resolved.

In the next couple weeks, I hope to have my ring issue resolved and the drive sprockets assembled.

All Stressed Out

Making a scale tank is not a new idea. However, making one without a frame is. I have yet to see anyone's scale project that didn't have a frame. Real tanks don't have a frame. The armor is thick enough to provide ample support for the vehicles weight and any stress that may be encountered. That's not to say that there are not "frames" inside a tank, i.e. support frame for the transmission, main gun, engine & etc. Most of these sub-frames merely provide attachment points for the various equipment in a tank. The big reason none of the other scale projects are frameless is mostly due to weight. A frame with a skin of plywood or sheet metal is significantly lighter than steel plate. But being hard headed, I decided to buck the trend and go the heavy metal route.

The big question was what was the minimum thickness the steel plate needed to be, but still provide adequate support? From I planning standpoint, I started out with 1/4" plate. I was pretty sure that if the whole skin was made from 1/4" plate, everything would be strong enough. That would put the weight of the body (outer skin only, not tracks, suspension, engine & etc) right at about 2000 lbs. Which means by the time I added everything else in, I was looking at about 5500 lbs. 5500 lbs is starting to push the limit of my suspension, hydraulics and tracks design. So in an effort to reduce weight, I asked for some help from an engineer who frequents the scaledtanks.com forum.

He took my CAD design and fed it into a program to evaluate stress on the body of the tank. We went through several different combinations of steel plate thickness before we came up with a winner. The combination I finally settled on was the floor of the tank in 1/4" plate and the rest of the tank in 1/8" plate. In addition, there was some angle iron added to specific joints to help reinforce high stress areas.

In the first picture, you can see the effect of a 2.5 G (61625 Newtons) strike on the left front road wheel axle hub.

The color scale shows the "buckling" of the plate. Blue, green and yellow are ok; red is bad. As can be seen, there is just one small area of red in the front corner of the right side sponson. The next two pics are of different angles.

So what does all of this mean? By using the thinner plate with some reinforcement in key welded joints, approximately 800 lbs and $600 in material costs will be shaved off of the project. I'll call that a victory any day of the week. :)

A thread on threads.

I have continued to cut out parts for the suspension. Almost all of the stuff being cut out of 1/8" plate is done. I am also trying to make my torch a little better at cutting out multiple parts. I have a cutting jig that works well for circles. However, cutting straight lines and cutting out multiple copies is not the easiest. The plasma torch does not have a drag tip so it has to stay a certain distance from the cutting surface. Also, the sides of the torch's head are angled making it harder to be perpendicular to a fence. So, I took a piece of 1" schedule 40 and made a doughnut for it to sit in. This keeps the tip at a consistent distance, gives my a perpendicular face to drag along a fence and allow the torch to sit in a consistent vertical position making the cuts more accurate. I would love to have a CNC table for it, but even a used one is big dollars.

However, I have spent most of my time battling threads. Each road wheel swing arm has a 1" diameter spindle and a 1" diameter axle that has to have threads cut into them. Plus each return roller (6 total) has a 1" diameter spindle. That is 38 total. I was having quite a problem initially. The round bar kept slipping in the vice. I then took and tack welded some pieces of flat bar to the round bar giving the vice enough flat surface to keep it from slipping. Even with the fix in place it is still a very tough go at it. It takes a lot of horse power (man power more accurately) to turn the die around the round bar thereby cutting the threads into it. I have five done and am seriously thinking about trying to find a machine shop that would take pity on me and give my a good price on cutting the rest. They would use a lathe and probably cut 20 in in the time it takes my to do one.

I have also had a couple of other smaller projects that have been a pretty big distraction. I made a friend at work a small waggon for his four wheeler to pull through the woods and I made my loving wife a new plant stand. Both projects were good for the tank project though. I used them to practice banding metal which I will have to do, in spades, on the tank.

Next up is cutting out the parts I need from 1/4" plate. Hopefully I have learned enough cutting on the 1/8" plate as mistakes made cutting 1/4" plate get expensive, fast.

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.