GoKart Tank

After much introspection, it looks like I am going to make some changes:

• 3D Printed drive and idler sprockets at 17 teeth instead of 11
• 3D Printed road wheels (yes, printed), but also at 17 teeth, that will raise the chassis of the tank higher off the ground.
• Move forward with making the tank based on a metal frame instead of a wooden one. 2 of the 2x4s will be recycled as longitudinal support members
• Fiberglass surfaces so that the batteries can be mounted inside the frame cavity

Plastic wheels and sprockets will save the track a lot more, and based on initial estimates will suffice for prototyping. They may not handle heavy duty operations, but it's pretty easy to cast aluminum replacements afterwards. I do intend to print in PLA at 100% in-fill.

Here's an image of the sprocket/idler:

Everyone who commented on the Hackaday article is saying I should stick with my 1KW motors. So I went back to the drawing board amd redid a few things. I think I can, I think I can. Meanwhile, as I wait for the tank to return from April's STEM Faire, I started mocking up an idea for eliminating the need to tension the tracks beyond a certain point. That does involve letting the track 'sit' on the road wheels. I will be testing this idea in miniature....here's a picture:

I wrote an article for Make on the tank and you can read about it here:

http://makezine.com/2017/04/05/gokart-tank/

Enjoy!

I am debating V2.0 of the tank to abandon the wooden frame and go with all metal. Here's what I am considering:

When I moved all my servers from my CoLo, I also brought back all these rails from the server rack made of 1/8" powder coated steel. These are L shaped rails that have one piece that slides into the other so that you can adjust it for different length/depth racks. I have maybe 10 of these things (for 5 servers). These aren't the ball-bearings sliding rails. They are fixed. They are strong, heavy duty, very solid. I measured them up and I have enough to make a pretty big and solid metal frame to replace the wooden one. I also have a lot of sheet metal from my airplane builds, tons of rivets and of course my drill. I think I can make a solid frame out of these left over materials that I would otherwise have to give away or sell off for peanuts. Yeah, I think it's viable. In addition, I have 2 dead 4U servers I had custom built years ago. The cases themselves are also steel. Bolt those onto the frame and you have a full enclosed box frame that is rigid and hollow AND fireproof. My thinking is that I can make a box frame with panels and a hollow space to install batteries, electronics and whatever else I need using recycled computer junk and still make it look good. Here is a grainy picture of the tank with one rail laying on it.

And here is one of those cases. Pretty hefty.

What do you think?

I have refined the suspension arm after 3 prototypes. 2 arms side by side with the shock in between. Bearings press fit and epoxied in place and we are ready. The arms themselves are 3D printed. And when I tell you they are rigid, they are super super rigid. Before I mount them, I will treat them all with XTC3D to weatherproof and of course make them even stronger.

Yes, it may be finished, it may be working, but it's time to get improving. Before I install the gasoline motor and differential (and triple the power), I am adding suspension. I've 3D printed the prototype to test fit stuff before I send the drawing off for the arms to be cut out of 6mm alumimum.

Phew. All done and ready for the Maker Faire. And it runs and runs great! In the end, I learned:

1) My choice for track works well in one direction only. Going in reverse throws a track

2) 2.5HP is not enough

3) I over engineered it in the effort to make it 'Heavy Duty'. I should have stuck to a metal body

4) I would use straight through axles for the road wheels. I have 16 pillow block bearings there. Each weights close to 3lbs. I could do fine with axles and 8 bearings instead.

5) The lexan sprung bogie is not strong enough for heavy duty work. I have to switch to metal

6) Electric is not the way to go for something this heavy. The motors are way too heavy and the 8 batteries are killer in terms of weight.

But...I love it!