MarkChibi Part 2

Wow... it's been awhile blogsphere. Life things have kept my busy with some sporactic working on projects in between. But MarkChibi has been finished! And rebuilt several times...

The original design involved 2 speed gearboxes from the FIRST Robotics world, dog shifters made by West Coast Products. They basically have two gear sets inside and then you choose which one you want to engage with jamming a "dog" gear with teeth into which set you want. They work great in the FRC world but with the much higher power and the lack of pneumatics on the karts it didn't pan out....

This was the first setup the night before OC Mini Makerfaire 2013, which was the deadline for the first built (yeah that was a while ago...). In the end it was locked in low gear and ran the even great. And some more "product shots" below. I guess in my rush to finish the cart I didn't really take many in process shots...... 

Steering... this will be something that gets talked about more. 

Fancy shot

So a few things learned after this.... need a better solution for shifting or just do away with it. Brushless motors have plenty of toque. Colson wheels without suspension on anything but the smoothest concert required painkillers, and the brakes.. to say the least need some work. 

 More to come later. 

The MarkChibi Part 1

Back a few posts, and awhile ago I mentioned I came across a guy named Charles and some of his work including. Now having actually meet the guy and going though the process of building my own Chibi a death-mobile it's my turn to write an short novel (nanowrimo) with photos of what has happened over the past few months.

It started with taking apart Charles' CAD and figuring out what kind of resources I would have. Currently most of my work comes out of our local hackerspace-Makerplace. Similar to the well known techshop, it provides a full wood, laser, craft and metal shop to anyone that pays the month membership and passes basic certifications on the equipment. With a range of equipment including CNC mill, bridgeports, and lathe just about anything is possible. However Makerspace has a lot of cons but those can be another very long blog post.

Do I need a bigger mill?

And well basically with all my projects it starts with an sketch in Solidworks, my preferred choice of CAD program. Which I have kinda learned how to do over the years of clicking buttons till things happen the way I wanted them to.

CAD! A complete mess of a model atm

Basically what the model looks like today when I opened it up (created date of the assem says May13). Mostly a hacked together mess at this point after many iterations and test fits and upgrades and whatever else I did to the poor thing. But the general construction is there, and how everything is put together. Basically when I started I had a list of points I need

• Must fit in my trunk without lots of disassembly 
• Must go fast.. 30mph? lol.... 
• To do the later 2 speed gearboxes
• Decent control and handling
• Budget..... or lack of therefore more on this later. 
• And to look awesome

With materials I had in hand I went with a regular 6061 extruded box design, held together with gussets and a bunch of 1/4-20 bolts. It's basically how I built several FRC robots in my past. It's cheap, quick and is pretty strong for how light it is. The frame is pretty simple, I went pretty bare bones with everything in the build, squares and simple shapes.

This will be it for this post more to come soon. I am currently in the process of upgrading MarkChibi for the San Diego Maker Faire Dec .7

The Chibikart

One fateful day while roaming the vast Internets I came across this: youtube link

Of course I wanted to build one after the first 10 secs of the video... and then a few weeks later: Instructables 

So after some pondering, and misguided thinking [always fun] it turns out this is something I could do, provided I get the funds. Makerplace has all the machining I would need for all the parts, the CAD model I can re-create and tweak a bit to fit something more to my tastes and tooling. And anything I didn't know/couldn't figure out can be redeemed by a few hours online, seeing there is quite a few people into this.

Personally a Solidworks user, a few hours in CAD and:

For anyone that has never used 80/20 it is cool stuff, being able to bolt anything to it without drilling holes is a bit of a god send. Of course the downside it is heavier then box and is a bit more expensive but for a project this small well worth the convenience. The frame is held together with 1/4 plates on the corners that double as wheel mounts. The main machining work that needs to be done is just 2d work on 1/4 and 3/16 inch plates. However unlike the DPRCibikart I have redesign the wheel and motor mounts with blocks and L brackets because I have access to a full sized mill. The steering "wheel" is something I might play with around more. And I am considering making the entire frame a bit longer but need to figure out the ergonomics of that first.

Electrical wise a pair of TURNIGY SK motors and controllers makes the round thingys in the back spin really fast. The exactly motor and controller combo is still up for debate, personally I want something with more power then the DPRC, but we will see how far I can stretch a budget and how feasible it would be for me to wire/program a Hall effect sensor. Using FRC CIM motors, gearboxes and controllers was considered for a bit but figures seem to show that buying all of that vs buying what I need for a brushless setup would require the same budget and the brushless is more effiecent and lighter. That leaves the problems of batteries which could be a whole post on it's own so lets not go there. Just suffice to say there will be 15-20AH at 24vs providing the power.

I also need to do some math to figure out what kinda reduction and wheels to put on, as this is not a blatant copy of the DPRC [okay maybe it is...], going to 6inch wheels with more reduction sounds like a good idea, or maybe not need to figure that out. Since 6 inch wheels allows for more reduction without loosing top end speed which should result in more torque. Personally my first goal with this is to make something that will give me a heart attack every time I or anyone comes near the pedal; quite a immature goal I know but I can't help it. I like speedy things.

The only problem in all of this is money, it an't cheap. About $800+ it is quite the under taking in the world of things I have done. With FRC being funded mostly by sponsors this is going to require some piggy bank cracking.

But damn would this be cool. :3