Sunday, July 7, 2013

The Brick Chronicles: Catalytic Converter/Exhaust Manifold (?) Phase III

A little over a month has passed since the last installment of the Brick Chronicles, which was semi-intentional. The brick has done about 2000 miles since, providing a legitimate testing period for assessing the state of the exhaust. Buttoning everything back up was trivial, so it wasn't post-worthy anyways. Time for Phase III: testing.

A few observations post-operation.

1) The "check engine" light has been on almost the entire time after the repair (I honestly can't remember when it first turned on, but it was within the first couple hundred miles). I suspected that the oxygen sensors were put in backwards, but that is not the case. I have noticed appreciable lag in the engine response, especially in situations like a 4th gear pull when trying to change lanes on the highway (i.e. low torque scenario). This is an entirely haptic observation but I've been driving this car long enough to notice these things. Most likely, the oxygen sensors needed replacing and/or were damaged in the installation process and are now mucking up the ECU reading; which would throw off the fuel injection mapping. 

2) In the last few hundred miles, the exhaust has gotten significantly louder, lower pitched, and sketchy-sounding in general. I think the clamp between the cat pipe and muffler pipe has been working itself loose over time. I bought some cherry loctite for the clamp hardware so that should be an easy fix. 

3) Most concerning of all, there is a clicking noise which is very clearly linked to engine RPM. While I was skeptical about there being an exhaust manifold leak, I think that a healthy dose of - not always smooth - highway driving has evinced the issue. This one will be harder to check, especially because I'd have to submit myself to carbon-monoxide poising to check it. Maybe I'll cave and let the shop diagnose this issue. This may also be contributing to observation 2. 

After addressing 2, I'll probably take it to the shop to avoid the dangerous fumes. It would be fun to do all the OBD II diagnostic stuff with an oscilloscope, but I don't have access to one currently (grad school soon!). Definitely making a good case for that pocket scope I've been procrastinating buying for forever.

But it's not all bad! After all, the brick has traveled another 2000 miles in sweltering heat and not broken down once. In other news, I was able to sell the old catalytic converter to the gentlemen at Davis Converters for a profit of $101. They won't reimburse you for shipping, but they sent a check for $128 and it was $27 to ship so that opens up some room in the budget to address the above issues. Interestingly enough, on a recent 900 mile trip I also monitored the fuel economy in both directions and the results were fairly consistent with what I used to get: 28.7 mpg there, 27.9 mpg back, versus about ~ 29 mpg in the past. The A/C was on full blast the entire time too so I was pleasantly surprised :)


D.E.C. catalytic converter - $396.55 (FREE SHIPPING!)
+        Exhaust flange gasket - $3.95
+     Oxygen Sensor Socket - $17.00
- Catalytic Converter Sold - $101.00
=                                         $315.50
($2000 - 315.50 = 1684.50)

Friday, May 24, 2013

The Brick Chronicles: Catalytic Converter/Exhaust Manifold (?) Phase II

Last time, in the Brick Chronicles, I had just ordered a catalytic converter. Since then, I've gotten to work on Phase II: Installation. With most people clearing out after graduation, I had a nice shady corner of the parking lot to myself. After all, I guess I am now a "shady tree mechanic."

Ad-hoc parking lot garage setup.
The jack setup in the picture above is rated at 9 tons (safety factor of about 6!). Anyways, the cat is split from the pipe that once connected it to the muffler, so the first step was to remove the section that was severed and not perturb the muffler pipe. The interface is this rusty two-piece bracket, which as far as I could tell was kept together by the remnants of some kind of pin. I pried the bracket apart using a flat head screw driver and some pliers. I honestly believe this is the procedure Volvo intended because if you're changing the cat then it follows that your hardware is ~15 years old.  

Rusty bracket.
Removing the brackets revealed the rusty pipe interface. I was a little concerned that this connection was welded at first. However, after blasting it with penetrating oil and torquing the free pipe with adjustable wrenches in opposite directions, it twisted right off. 

Rusty tubes.
Ta da.
Enter, the stubborn oxygen sensor.
With the pipe free, I could now access the downstream oxygen sensor. It makes most sense to remove the entire assembly before extracting the sensor because the pipe is free and unwieldy to secure. Before removing the pipe, a skid plate is blocking the sensor wire and must be removed.

The wire is held to the frame via a series of clips which I pried up with a flat head screw driver. I did not have a good means of fixing the pipe in place in my parking space garage so I actually ended up following the wire up to the wiring harness in the engine bay, and removing the whole thing from the car. Remove the air distribution hose from the filter housing to access the wiring harness.

The silver washing machine hose like thing is the air distribution hose.
The left connection goes to the front sensor, and the right goes to the rear. There are red clips that you can pry up. At this point - poking around with a screwdriver in the engine bay - it would have been wise to start doing things one-handed because the chassis is live (floating ground). I elected to take off my watch and try not to touch things.

Oxygen sensor connectors.
One piece.
Moving on the oxygen sensor extraction, I'll start by saying how you shouldn't do this. I tried to take a shortcut and extract it while the wire was still tethered to the car; with the available slack, the assembly reaches just a few inches outside of the frame. I'm not proud of this, but my plan was to wedge one end of the pipe under my front tire and get a foot on the other end while wrenching on the sensor. Attempt one involved a liberal dose of penetrating oil (probably five coats all told) but was not enough to sufficiently break through the fillet of rust fusing the sensor to the pipe. No dice. For attempt two I lit a small fire (I hope nobody from DOTS reads this) and roasted the threaded part of the tube, attempting to expand it and release compressive stress on the threads. Still nothing. A third method involved melting candle wax into the threads to lubricate them. This failed because rust almost entirely concealed any access to the threads, and was admittedly only attempted because I read about this trick online and how cool would that have been if it worked? All of these attempts were useless because my method of constraining the pipe with tire and foot was JV at best.

Once I finally detethered the pipe/sensor assembly the sensor came right out with the help of a vice and a big wrench with a pipe to make it even bigger.

A more sensible strategy.
So, that's half of the cat removed and one oxygen sensor (of questionable functionality) salvaged. I am optimistic that the sensor still works and am reading into ways to diagnose this without a legit OBDII scanner (i.e. using an oscilloscope). We'll slate this as a problem for future self. Next up, I will remove the upstream oxygen sensor and the larger part of the cat, which is buried deep in the engine bay. Here's the updated scoreboard:

D.E.C. catalytic converter - $396.55 (FREE SHIPPING!)
+        Exhaust flange gasket - $3.95
+     Oxygen Sensor Socket - $17.00
=                                         $416.50
($2000 - 416.50 = 1583.50)

In the green for now at least. You can borrow oxygen sensor sockets from Autozone free but I figured this was an investment for future brick chronicles and car repair projects. Until next time.

Thursday, May 16, 2013

The Brick Chronicles: Catalytic Converter/Exhaust Manifold(?) - Phase I

I've had it.

The other day I was driving in my '98 Volvo S70 when all of a sudden I heard this terrible noise resembling an old Civic with a cheap aftermarket exhaust kit. I panned left and right, initially thinking it was one of my road neighbors, until something bad happened: I changed gears only to hear this horrendous low-pitched babble following thine own engine RPM. Fortunately, I had only made it a few miles away from school when this all happened. The brick is a 15 year old car and according to the service history the exhaust hasn't been touched; it all made sense, I thought to myself as I poked around the car awaiting AAA. I had it towed to a garage near campus for $24 - cheap insurance in case my -- still driveable -- Volvo has something more serious it was hiding.

Old cat cantilevered off the exhaust manifold. 
The next morning, I awoke to a call from the garage owner who diagnosed both a failing exhaust manifold and catalytic converter, with an estimated price tag of $2,000 parts and labor. This far exceeded my premonition of a bad connection between the tailpipe and muffler. However, for those reading who know me (and my brick) you know that it takes a large number to startle me when it comes to car repair. This is the same car which had a timing belt tensioner fail in Canada, costing about $1,300 in towing and $3,000 to replace the engine. Other holes in my pocket include the time I went to prepare my car for a road trip and wound up with a $1,200 bill to replace A-arms and tie rods with worn ball joints and $400 for a radiator that one time. Fortunately, I have a habit of working year round and am able to fund my aging automotive sidekick.

Disaster strikes in Montreal.
This summer, though, I will be taking a rare break. For in the Fall I shall be blossoming into a beautiful graduate student butterfly, and heading the advice of every grad student I've ever talked to ever, I'm taking a damn break! I cannot remember the last summer like this (I think it must have been when I still went to summer camp) but it gave me an idea: now that I have the time, I can finally work on my car myself. That, combined with the realization that I now have a degree in mechanical engineering. I think this also certifies me to assemble IKEA furniture sans directions?

I guess this is a somewhat pedantic and anecdotal preface to the main point of this and future posts. This is that I'm sick of blindly paying garages to do work I can do myself -- putting on my DIY car repair hat. I picked up the car immediately after hearing the garage quote, had a loud, slow, and nerve-wracking drive back to campus, and then immediately began Phase I: Research. I scoured the internet for parts and such and found the Volvo original exhaust manifold (which I am still not convinced is busted) could be purchased for $431 or about $75 from a junkyard, and the catalytic converter for just $395 if I don't plan on driving to California anytime soon. With the latter not meeting California's strict emissions regulations, I could cut the cost of the part in half and then some. So at worst, I pay $1000+ and learn something, and at best $400+ and I still learn something. And in either scenario, I can't go to California. Seems reasonable, so I bought the cat, in addition to some small supporting hardware.

Strangest object to be delivered to the front desk. Probably the most chemically diverse as well.
Guess I'm not driving to Calif. any time soon.
This concludes Phase I. Let's review the score:

D.E.C. catalytic converter - $396.55 (FREE SHIPPING!)
+         Exhaust flange gasket - $3.95
=                                         $399.50
($2000 - 399.50 = 1600.50)

Off to a decent start! The next steps are to get the tools together and then do the actual work. Oh and graduation somewhere in between...but that's a completely different kettle of fish.

Monday, January 21, 2013

TOBL2: First Rolls

TOBL began as an idea that popped into my head one fateful night in the Fall of 2010 - sometime around here. Two years and a few months later, TOBL the sequel, is alive. Thinking about it this way, I'm not too far off Apple's new product release pace. In fact, TOBL original was controlled by my iPhone 3GS, where as now I have an iPhone 5. Interesting. Well, without further delay here's video of the first recorded rolls:
I cannot think of a more appropriate place for TOBL2 to be initiated than the filthy floors of the hallowed MITERS shop. After all, this is where the first TOBL was forged and where I learned most of the skills needed to create TOBLs. Okay, onto the technical part.

The numbers:

0.8 lbs
22 screws and bolts
6 wheels
2 bridges
7 different belts before getting just the right size
5mm of ground clearance
And my favorite: TOBL2 has traveled to and was worked on in 3 different states

To get to this point there were just a couple agonizingly simple loose ends to address. First was the belt and tensioning issue. Two posts (and four months!) ago, there's a picture of TOBL fully assembled and seemingly a few 1s and 0s away from action. However, the belts used in that picture were so tight they stalled the motors. Thing I learned: the pitch diameters given for FingerTech belts aren't precise enough to be designed around. I designed the whole pattern on the side plates to the millimeter to get the belt tension just right, but went through seven different belts and three different pulleys before hitting a winning combination.

Two: the radios. My brand new pair of xBees which I paired and updated the firmware on weren't talking to each other, I thought. Turns out I was using an older REV of my XPWMShield that was assembled incorrectly, denying power to the xBee on-board TOBL2. After fixing this and re-flashing the xBees to a wireless programming friendly bit rate of 57600, wireless communication was restored. I also learned a neat trick for wireless programming: when uploading the new code hit the Arduino reset button just after the program size pops up. There are fancier ways to achieve this automatically if you plan ahead a little with your circuit, but this works fine so long as you can get at the reset button! Wireless programming is a stupidly awesome upgrade for the TOBL line because otherwise there's no way to access the USB programming port.

After being shelved for months that was seriously all that needed doing...took me about 6 hours yesterday. With my volatile lifestyle and imminent graduation who knows how far I'll get on this list, but here's what I would like to happen next:

1. Clean up the wiring. A healthy application of zip-ties and more flexible wiring should take care of that. Needs more wall-flips.
2. Incorporate the servos that currently serve no function except a slight amount of structural integrity. They were intended to auto-tension or de-clutch the belts. This is mostly a mechanical task.
3. Develop the controller. My Python controller is quite rudimentary at the moment. I run the program in the shell, click on a little box, and then have the following discrete abilities: forward, reverse, left, right, and hard stop. The next step is to add speed control and a little calibration to account for unequal belt tension. A GUI would also be nice to trim different parameters.
4. IMU? Well, I am taking a controls lab this semester. Maybe I can use TOBL2 as the platform for some kind of controls problem like directional stabilization? The motors probably aren't fast enough to enable Segway-mode. Shame.
5. NEW ELECTRONICS. Bet I can take all the functionality of XPWMShield and MKI and put them onto one wireless motor controller board with a smaller footprint. It would also be nice to ditch the expensive Arduino Nano and just run straight off of an AVR chip with the Arduino bootloader. Regardless of whether this new batch of proprietary electronics makes it onto TOBL I'd like to have a more polished and convenient package to work with for whatever project comes next.

Time to go back to school.

Monday, October 29, 2012

Courtesy of Sandy

As I was sitting eating some yogurt on this rainy morning, I realized how much I miss working on my small robot friend TOBL2. Same story as always: school and my innate propensity to occupy my free time with responsibilities. Quick semi-relevant aside: I am loving being a TF this semester! The class just made the transition from the instruction-based part of the semester, to the build-and-test-an-autonomous-hovercraft portion. Already my inbox is being flooded with messages about batteries selection, which sensors to use, how to wire everything up, Arduinos (I know), etc.. In a way this class has curbed my appetite for making things, which is a nice side effect.

Anyhoo, I thought I'd share a video of TOBL2 in his current state. That is, a glorified python-enabled motor controller.


Not my finest cinematography but in the video you can see the directional keys have been mapped to forward, reverse, left, and right. There's a hard-stop function tied to the space bar as well (not shown). In this configuration, there's no speed control (I know booooo) but I will add two keys to increase and decrease speed. A lot of the controller specifics will be tweaked once I get the thing moving and can see what makes the most physical sense.

Speaking of assembling TOBL2, there are two factors impeding that from happening. The first is that no combination of the belts and pulleys I bought seem to work. Even with the nice auto-tensioning, one belt is just way too big and the other stalls the motors from being so tight. I am placing an order for some new smaller pulleys and couple different belt sizes. Selecting those was more scientific that I just made it sound, so hopefully I'll be able to drive this thing finally. The other road block is the wireless issues I've been having. Probably not a big deal, but I don't have much in the way of debugging those issues unless I go to my lab. I'll look into that once I get a working drivetrain.

Welp, thanks Hurricane Sandy for the little break from classes. Time to get caught up on everything else...

Tuesday, August 21, 2012

TOBL2: Press Pause

This past weekend my hard drive kicked the bucket. It's kinda my own damn fault. My external hard drive died a while ago, my computer started wheezing a bit in the Spring, and I didn't do anything about it. But I guess that's what you get for moving around all the time. Hopefully it can be recovered at some point, though it will probably be expensive.

Progress on TOBL2 is at a bit of a stand-still while I resolve computer issues (currently booting Ubuntu off a flash drive w/o a hard drive), finish up my summer internship, and transition from Colorado back to Maryland. But don't fret! It's really quite excruciatingly close to being done. Check it out:

Essentially needs code (old code is now gone :/)and some slight mechanical tweaking to get the tensioning spot on. Next time I'll take it apart and show off some of the cool machining I did last week.

It also turns out Maker Faire extended the Maker application deadline (shock) to this Friday, but it doesn't look like I'll be able to take advantage of that. More likely TOBL1 will be used as a placeholder get to get in the door. Can't do much about a hard drive dying so I'm proud of how far I got. I'll press play again after relocation.    

In the meantime debating updating computers a year earlier than anticipated...

Saturday, August 11, 2012

TOBL2: Build Week 2

Sitting down feels nice right now. This week was quite a push to keep TOBL2 on World Maker Faire schedule. If I'm honest, I don't think I'll be able to pull off a fully functioning bot for the August 17th deadline,  because I need to focus on my actually work work. A TOBL2 running the old iPhone controller or maybe a short autonomous program and no servo clutching is definitely still possible. So that's what I'll focus on. But I'm getting ahead of myself, here's where the bot's at after this week.

I tend to stay in the machine shop until the time I need to leave to make up for it coincides with the start of the afternoon mountain rain. Cold, but totally worth it. This week I machined all the mounting blocks which resolve the 90 degree angle between the drivetrain and electronics shelf. Remember the ridiculous custom stainless steel standoffs I made for TOBL1? I suppose these mounting blocks would be the machining analogue to those standoffs. Except machining really small things beats machining stainless any day. By a lot.

Here they are. The two on the left are for the battery tray and the four on the right support the electronics.

The only issue I can spot so far is the taper on the electronics plates from the water jet. The sides of these plates butt up against the motor plates and create a little gap. That's easy to fix.

The motor controller diodes also appear to be impeding one of the servos. That's another easy fix.

Oh yeah, and slightly more troubling issue: the belt appears to be undersized. I need to cut the motor shafts before attaching the outer plates and knowing for sure, but it's looking a bit tight when I just hack it together. The next size up belt has three more teeth so I'll probably invest in a set of those. Don't really need to worry about the slack thanks to the torsion spring tensioners.  

Still left to do (mechanically):

1. Add springs (coming in the mail Monday)
2. Shorten mounting blocks to make way for servo
3. Grind down electronics plates
4. Cut motor shafts, attach outer plates and see if belts too tight (if not skip 5)
5. Replace belts
6. Assemble 
7. Add servo linkage (probably won't worry about that 'til post-deadline)     

It's a bit ridiculous to go through every little mechanical task that needs doing, so ignore that if you like, it's really just a reference for me. This is definitely doable in 5 hour blocks of machining. I'd like to be done with this list by Tuesday, leaving the last three days to wire it back up, get decent code running, and capture the required media for the Maker application. This week we should finally see this thing move! Build week 3 engage.

P.S. Last weekend I moved for legitimately the 5th time this summer. So that's why there's a new backdrop for my pictures every week. I think this is my favorite so far.