Friday, June 10, 2016

The 2016 MarkKart - The Beginnings

Again after a long lapse of blogging I am back!

The months of March and April were taken up by the fact a group of misfits and I built a 250lbs battlebot and ended up on Season 2 of ABC's reboot of Battlebots! That's a long story and I'll post a more in depth article on that when more of the NDA's get lifted.

But we filmed Battlebots up till the end of Apr, and due to being crammed into a huge hot sweaty room of roboteers we all ended up sick including me.... so after a recovery phase, I realized I had like 2.5 weeks to build/upgrade/do something for the Power Wheels Race at the Bay Area Makerfaire..... 

For anyone that doesn't' know yet, Power Wheels Racing Series  is a event hosted at various Makerfaires where teams show up and either mod a Power Wheels (kiddie ride) or build something that ends up looking like a Power Wheels for under $500. And race it around a small-ish track in the parking lot of a Makerfaire, and perform a skirt for audience votes to collect "moxie points".

So with the state MarkKart (or whatever it's called now) was left it needed some serious work. Burnt motor(s), way to high CG, handling issues and a frame that was 3 years old. 

The 2015 kart... 

And a dead Sk3 outrunner
So after thinking about it... a complete re-design ended up happening.... oh hi solidworks: 

Missing some bits.. but close enough
The CAD for Markkart 2016 have been in the works for a bit, but during the first week in May while recovering from robo-pox I got to a point where I was pretty happy and could start fabrication. It is the most gokart-y looking thing, I've built so far. It started out more chibikart like and kinda evolved into more of a 3/4 sized tinykart thing.... THANKS SHANE.

I'll break up the different parts of the MarkKart build in to various post (making this up as I go) to hopefully cover the project in greater detail then I usually do. (Charles' blog is the inspiration there).

Having always done bolt together alum tube extrusion frames on the past karts (I have a burning "dislike" of 80/20). I decided to try something new, and that is having a frame welded together for me. That's right, OUTSOURCING. Over the years welding is a skill set that has eluded me, and TIG welding aluminum is up there on the welding difficultly level. So to be able to get this done on time and with the quality needed, a ringer needed to be brought in thankfully we have an amazing welder at the local Makerspace that got the bid.  

Frame design was probably the easiest part of the CAD, all 1x1x.125 6061 square tube and all done up with right angle joints. With some round bar welded in for the seat mount (razor ground force seat).

Boring I know right
Yep pretty boring.
Overall dims are 30x40. To ensure it could be welded quickly enough everything was designed so all the welds were with same thickness material and butt joints at 90 degree angles. Basically the drive boxes bolt on the back. Spindles go into the front gussets a seat in the middle.

But Markkk this isn't what a gokart frame is suppose to look like...... 
A real cadet kart bare frame

To get philosophical for a second here..... I am well aware a square thing made out of box tubing isn't exactly consider a "real gokart" depending on what circles you run in. Due to limitations of time and everything else something quick and simple took precedence over everything else. Also round tubing used in real racing things, is a challenge to work with and with little experince in that area trying to bend and jig up a real ish looking frame just wasn't gonna happen. Also on a personal level this is project wasn't meant to build the fastest or the most "real" gokart possible, but something fun and silly. So yeah square tubing frame for now. Maybe something different next year...

A hindsight thought is I have learned a lot about gokart dynamics and handling over the course of being around PRS for a few years. Some of the teams are legit and have built some really cool stuff (photos later) and talking to them has taught me quite a bit.... the limitations of the MarkKart has always been my design abilities for vehicle dynamics but that's improving over time... (FIRST and it's skid steer sigh).

Anyways onto the build! First trip to the local metal yard for a bunch o aluminum.

Then drilling the mounting holes needed for various gearbox and paneling bits on the Bridgeport.

So with welding, the biggest worry I had was making sure everything came out square. If you look at the design the front bar and the rear bar actually bolt on with gussets. This allows the drive system to come off and on easily and also provided a jig within the frame for welding. I was able to bolt it together, ensure square and then hand off the bars and part with a drawing to the welder. So he could weld in all the middle pieces. 

It's a rectangle
The black magic of welding
After about 3 hours of welding it was done! Honestly it went together faster then even I expected, and the final product was awesome! Everything within a 1/16 or better, and dead nuts square. 

Looks like the CAD model... weird how that works out..
Next was adding the paneling to hold the electronics and batteries, the 1/8 alum was going to be waterjet cut but they ran out of time on the machine so I ended up using the local CNC plasma machine. Not as clean of cuts but with some filing afterwards still works fine. 

CNC Plasma is stupidly fast
 Because I was worried about the holes lying up after welding, I didn't put any of panel holes in the frame. So had the plasma cut them in the panel, clamped it together and matched drill.

Only use for SLAs le
 Bind pop rivets are a personal favorite of mine, these are 3/16 aluminum ones. And with a $40 Harbor Freight pneumatic rivet gun they take seconds to install and make for a clean look since you can't see anything from the top.

 And it's done!

Notice the stockpile of spray paint in a photo above? Something I've learned is that just simply painting your projects makes them go 10x faster... well maybe not but it makes them look 10x legit. And makes other people think you're more legit.... since I was waiting on waterjet parts and various things to come in I figured ill go give it a try. Painting aluminum is always a bit tricky due to the fact nothing likes to stick to it. (Wanted to do powercoat but no time). 

From what I have learned, it's best to sand everything with a 300-400 grit disk sander to get the oxidation off the aluminum, this also buffs out most scratches and such. Then to lay down 2-3 coats of zinc based self-etching primer. Afterwards then 2 coats of your color. Paint of choice was rustoleum spray paint from the local Homedepot. 

Zinc primer is always greenish
That looks legit now eh. 

We'll see how this holds up, the real trick was letting it cure for 3 days untouched. As most paints don't fully harden for days so assembly will need to be carefully done....  At this time waterjet parts come in and back from coating! So fun times should be had teaser for next post:

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