13 Plans for a New Year

We're all making New Year's resolutions. I have a few personal ones of my own, but they have nothing to do with this blog. This being Yet Another Mechanical Engineering Blog, I will focus on my engi-nerd-hack-robot-ing goals for this year, or at least the coming IAP (January semester) and Spring semester. 

0. Tune Up Cruscooter

It's a dirty hot mess. Needs major rewiring. And a working brake. 

1. Build a semi-autonomous Quadrotor

WAY more details about this coming soon. This will be one of my first projects of IAP.

2. Build a Bi-copter/Tiltrotor. A la V22 Osprey. 

Something I've been wanting to do since I saw the attack choppers in James Cameron's Avatar. And something I tried to do last year when I knew nothing. Now I know a little something, and building a quadrotor will help give me an intuition for flying things. 

3. Win MASLAB.

It's a ballsy goal. But hey, I'm a freakin' engineering diva.

4. Finish MelonChopper

Cannot wait til I can drift this thing in the snow :p

5. Learn to weld steel.

So I can build Certified Legit vehicles. For cheap. 

6. DeltaBot.

I'm going to have the coolest thesis ever ^_^.

7. Write an Instructable on manipulator robotics.

I've learned a lot in the past few years, time to spread the love. But first...

8. Design and build a ~7-DOF robotic manipulator. A la KUKA arm.

I've been controlling these bad boys, now it's time to be a Mechanical engineer for once. 

9. Pay attention to TurtleBot.

Of my children, I've been giving a lot of attention to TinyArm and none to TurtleBot, and I don't think TurtleBot can handle neglect much longer :c. Time to turn that around. I owe Shane a SLAM map of the IDC before he goes off into the Real World (c). 

10. Get TurtleBot+TinyArm playing together.

I still hold myself to the dynamic duo, TurtleBot and TinyArm, getting me a soda. Maybe now that TinyArm has learned how to talk, and with the release of ROS Groovy Galapagos I'll finally make it happen. 

11. Learn ROS. Like really learn ROS.
Willow Garage released its sixth distribution of ROS today, Groovy Galapagos. It's cleaned up a lot, and is apparently easier than ever to use. It'll happen when I try and get TurtleBot+TinyArm to get me soda. 

12. Learn C++. Like really learn C++.
See above.

13. Get a summer internship.
I cannot spend another summer at MIT UROPing. I need to see the world. See what industry is like. I need experience. I need to make a difference. I'll probably apply in the next few days...

MelonChopper Build Pt.3: ROLLING FRAME!

RAWR! :D

Doesn't this thing look intimidating? Like it wants to hurt you? Muhuhaha!

Here's how it happened: 

The rear wheel assembly Bayley found on Ebay for like hella cheap came in! The 55-tooth sprocket pictured here is easily detachable and replaceable. Which is good. Because 100MPH is bad :c

Also here is the band brake it comes with, same design as the one on Cruscooter. It's larger, 90mm Diameter, I believe. 

I also found this giant hunk of plastic, Delrin I think. It was someone in the Heat and Mass Transfer Laboratory's final project or something, but it was thrown out next to the lab by all the recycling stuff. 

0_0 TAKE!

Using a bandsaw and a mill, I made two of these, each of which is an adapter between my steering column and a steering mount. 

Here it is mounted. 

Steering's (mostly) done! The wheels steer straight and the steering geometry works out just like it did in the CAD. 

This is scary, though. For reference, I was sitting in the gokart when i took this picture, the camera right between my legs. In order to steer this thing, you must have this menacing castration device called a steering wheel aimed right at your crotch at all times. I should put a sign on Melonchopper saying "Warning: Cup required to operate this machine. Violations will result in immediate castration."

I'll fix this problem later. First, the tire rod adapter slippage: 



I decided to use my spare face-mount shaft collar to attach to the tire rod adapter that kept slipping whenever I tried to steer, even if it was tightened like hell. I just drilled one .25" hole and fastened them together, which seemed to fix the problem completely. 

Only steering problems left are: 
1. There's not much leverage with the current steering wheel. You need to apply a lot of force to steer. This can be alleviated by using a larger steering wheel, magnifying the torque you apply to the steering column. 

2. The steering wheel is SO F**KING CLOSE TO MY CROTCH. WTF. This can be aleviated by moving the steering wheel as far down as possible (shortening the steering column by a couple inches). This doesn't change the steering geometry at all, and gets the steering wheel away from my precious, but moves the steering column axis even lower, requiring a bigger steering wheel to make it still comfortable. I can also move the seat farther back if I wished, though it would be a pain because of my crappy seat adapter design. I also need to make sure I mount and tension my motor perfectly before I even attempt this. 

But all that is for a latter day MITERS session. Now it was time to finally mount the rear wheel! Except... 

The shaft diameter of the axle that came with the rear wheel assembly was NOT 5/8", which is the standard for 10" pneumatic wheels -_-. It was actually 10mm, the same size that comes with the 8" pneumatics on Cruscooter. 

I could waterjet new plates with holes small enough for the rear axle, which would require time to get waterjet access and bad karma for abusing a waterjet even more.

I could drill 10mm holes into this existing plate, which wouldn't be as pretty or as accurate as waterjetting a new plate. 

I could  buy new bearings that would fit in this wheel assembly that would take the 5/8" I already purchased. Would take time+money. 

I could find parts lying around MITERS and make myself some spacers/bushings that would stay in place during operation. I went with this option, because I love using lathes and I WANT MELONCHOPPER ROLLING RIGHT NAO. 

I found myself a rather... interesting looking piece of Aluminum scrap. This was 3/4" diameter, which I could use to make the flange of my bushing/spacer/thingies. (The term bushing presupposes the shaft it supports will be rotating about it, which is not the case. So these are flanged spacer/thingies.)

Ahh MegaLathe, my favorite lathe on campus. It's simple. It's robust. It doesn't have a digital readout. It spins beautifully. It can take a freakin' beating. It is in the MIT FSAE/Solar Electric Vehicle Club shop, located a skip and a jump from MITERS. Some groveling and agreeing to clean up more scrap metal than I generated landed me some time on this baby. 

And away we go! 

One out of two down. Thanks to my darling friend and the team manager for FSAE Natalie Dostie for providing her hand modelling services :D

And they're both done. D'aww, look at my adorable mechanical drawings! :p

And... they fit! 
And I realize i need to tighten the 8020 fasteners BEFORE I mount the wheel. Derp. Another case of Things Dan Didn't Think About When He CAD'ed. 

A thing Dan DID think of when he CAD'ed was that the band brake assembly needed somewhere to grab onto, otherwise it would do all kinds of crazy things during operation/braking. And that's just what this lone 8020 fastener does for me. 

Now I needed to determine where my rear wheel mount plates should be fastened in order to ensure the rear wheel didn't interfere with...anything. I brought it as far back as I could, to within a quarter-inch of the 8020 butt-piece. 

I measured and copied down the distance between the plates part right here, so I could remove the wheel, position both plates and fasten them securely. 

Cool, 3/4". 

To ensure the two sides lined up, I fastened one end, attached the rear axle to line the sides up, and fastened the other end. Measuring both sides, they were accurately placed. 

Now the rear wheel's mounted! :D meaning...

ROLLING FRAME! ROLLING FRAME!

Upon placing my rear end upon the tractor seat for the first time, I realized a fundamental flaw in my design: THIS THING DEFLECTED LIKE HELL. 

Like REALLY. I sat down and can get about 45-degrees of torsional deflection by leaning side-to-side. This is because there's no significant cross-bracing between the two main 4-foot 8020 extrusions. Fortunately, the deflection is all in the elastic regime of the aluminum, and it appears there's no significant stress (Force/Area) anywhere along the extrusion. Just an mega-ass-ton(/tons, deflection is a unit-less percentage) of torsional strain, due to all the material that is able to move. 

There will be a bunch of material on the bottom for mounting the Battery, Controller, and other hardware, so it may just be an inexpensive slab of... something bolted to the underside. 

Makes me wonder, what if I had used welded steel extrusion instead of 8020? I think it would have been cheaper, but it would have also taken me way more time to put this together. I've never welded before. I kinda really want to learn, and make less expensive AND stronger vehicles with the technique. 

OH, this brings me to another cool point. This guy. (Follow his blog. FOLLOW IT!)  Jeremy is his name. And he's building his own version of Chibikart! And he wants to go to MIT, which, you know, is awesome, because he'll hopefully be another MITERS junkie like moi. 

While Charles Guan's Chibikart was optimized for time and ease of manufacturing (as in, you design it, you get the parts, you bolt it together, you ride around. It's more expensive, but faster/easier. MelonChopper takes in this ideology) 

Jeremy's Chipikart is a redesign of Chibikart that will end up costing about a third of its predecessor, because it uses cheaper components and manufacturing techniques. Chipikart is optimizing for cost in a very intelligent way, using steel extrusions welded into a frame, milled aluminum bars to replace the stacked wheel upright plates, etc. A truly inspirational build. 

And so, MelonChopper rests on her/his/its(?) winch bed for the night. Where it will probably stay until I return from winter break for MIT's Independent Activities Period (IAP). 

What adventures will await the DGonz during IAP? Starting work on DeltaBot? A Quadrotor with custom controller softwarez? A Mobile Autonomous System to be played with in a Laboratory? MelonChopperTroller? Custom-laser-engraved stainless steel hip flasks? (I turn 21 December 24) 

Yes.

Melonchopper Build Pt. 2: Waterjet abuse

Waterjet Abuse Pt. 2

I finally got a chance to waterjet the parts! Here they are laid out in OMAX.

I finally figured out what one of the issues I've had in past waterjet jobs is! I used placed tabs in my part before automatically generating lead-ins and lead-outs. The toolpath generator would then flip out and confuse parts and holes, cutting along the inside of parts and along the outside of holes. Turns out if I place tabs AFTER generating lead-ins and lead-outs, the toolpath generator is much less likely to flip the shits and screw up my part. Yay, knowledge

And away we go! Quarter inch parts first. Look at all them parts. 

And the quarter-inch job is complete! The steering upright design I copied off Chibikart needs one 1/8" plate in order to fit the 5/8" "axle". I realize now how little of Melonchopper is original and how much of it is lifted directly off of Charles Guan's and Shane Colton's respective Chibikart and Tinykart. Or rather, how much of other their designs I was able to utilize and integrate into my idea, which is the point of engineering, right? 

You spend time researching something and making something that works well so other people can use your accomplishment to make something even cooler. Than you can step back and say "Cool, (s)he used my design for one thing to make another. I'm flattered." If the wheel ain't broke, don't reinvent it. Because someone already spent sweat and time inventing it already so you didn't have to. 

Also, I've been getting better at the whole Tetris thing. Metal is "so espensive", and I want to use every last bit of it I can. 

Woo, parts! I love waterjetting because you can spend more time in design and less time fabricating. It's really sad that it's such an expensive and exclusive manufacturing process, but it's nice to be part of the 1% of people with free access ;D TIME TO START PUTTING THINGS TOGETHER!

Compiling my parts into Assembly

I start with the wheel uprights when...
Uh oh, compiler error. These retaining plates aren't fitting together. Time to start filing! Oh the joys of waterjet tolerances...

Oh the joys of waterjet tolerances...

While I dealt with the steering, Bayley put together the main frame. 

Filing out the holes and slots was taking too long. Instead, I took the tabs to a belt sander. 

MUUUUUCH better. Now I can put the hex bolts (my "wheel axles") into the assembly and have uprights!

OH FOR FU-

The bolts won't fit into the slots -_-. Nothing the belt sander couldn't handle...

YAY WHEEL UPRIGHTS! The bottom plate had smaller bolt holes than the top bunch, so that i could tap 1/4-20 threads and just screw the whole thing together. 

Now to mount the uprights. I had to place the upright bearings into these mounts before I fastened them to the 8020. 

OH FOR CRYING OUT LOUD. THIS WAS DESIGNED TO BE PUSHED IN WITH YOUR HANDS. Sigh...

Beasting it as usual, nothing to see here. 

Cool. Almost ready to mount.

All I need is a washer between the upright and the top plate for the upright mounting to be complete. Issue is, I forgot to purchase 5/8" ID washers, and MITERS didn't seem to have any lying around. They DID have 1/2" ID washers though, whose OD fit perfectly in the space...

"Bayley, we need to drill this washer out somehow. YES, this is the only 5/8 inch drill bit I could find..."

For ease, I ended up using a 5/8" endmill and these handy clamping doohickeys. 



YAY!

STEERING EXISTS! Now to start mounting the steering column. 

8020-1010 extrusion has ends that are perfectly sized to tap with 1/4-20. I did just that to mount a steering column support flat up against a plate. 

Like so. LOOKING GOOD!

This clamp is not enough to hold the tire rod adapter to the steering column. Good thing I purchased an extra face mount shaft collar for this thing, because I'm going to need to redesign this thing. When I turn the steering column, this just slips. 

These is a seat adapter plate. They are very poorly designed, because you cannot access the 8020 fasteners once the seat is mounted onto the adapter plate. Also, the screw that bolts down the seat INTERFERES WITH THE 8020. BECAUSE OF MY BAD/LAZY DESIGN :C. Oh well. 

You can see we stacked washers making room for the head of the hex bolt that screws into the bottom of the seat. 

I put together the 1/8" plates holding together Melonchopper's butt, as well as threw in the rear wheel mount and motor mount plates. 

OMG SO MUCH GOT DONE! It LOOKS SO PRETTY! Let's mount wheels and a seat. 

WHEELS AND A SEAT, OH MAN! More build coming up soon as I do it and more parts arrive.