Makerbot Replicator 2 Alignment Problems

If your Makerbot misaligns from one layer to the next, chances are you have a bad cable on either your X stepper motor or your X endstop sensor.  The cables are a little time consuming to replace because each cable attaches to X, Y, and Z motors or end stops, and feeds to the motherboard under the machine.  I replaced it with cables from Robotshop that have a connector to a small jumper cable on the X motor and X end stop.

Replicator 2/2X Cable Assembly E - XYZ Motor (Rev2)

RB-Mkb-01

Replicator 2/2X Cable Assembly D - XYZ Endstop (Rev2)

RB-Mkb-08

You also need the jumpers that make the last part of the connection - this is the part that fails due to the repetitive strain on the cable.  You need to buy at least one of each, but better to buy several so you can replace it quickly next time it happens.

Replicator 2/2X Jumper Cable - X Motor

RB-Mkb-02

Replicator 2/2X Jumper Cable - X Endstop

RB-Mkb-10

If you experience intermittent X axis motion, or grinding when the system does "Home Axes", this will solve your problem.

Not High Tech, but Technology in the Classic Sense

A friend recently wrote us asking about running out of hot water during showers, and it reminded me of a simple fix. She wrote:

"Hello friends and family. Can you please help me out? We are having trouble getting enough hot water for showers at our house. We just bought a new hot water heater, 50 gallons, and we still can only take two SHORT showers one after the other if we want hot water to last.

I have been doing a lot of research and calculations. Can you tell me about your own household? I'm wondering if my expectations are too high.

1) How many gallons is your heater?
2) Gas or electric?
3) Brand?
4) FHR #? (First hour recovery number is located on your tank) This number is important.
5) How long are your showers?
6) How many showers can your family comfortably take in a row?

Do you run out of hot water? I am going nuts!!!! I think we need an 80 gallon tank!!"

Generally speaking, gas and oil heaters can heat water faster than an electric heater, but this is just a common product engineering trade-off, not a law of physics. I replied that a 50 gallon gas or oil heater is a bit small for a family of four, and that it is definitely too small if it is electric.

Either the shower needs enough BTU/Hour (British thermal unit is the amount needed to raise 1 pound of water 1 degree Farenheit) to keep up, or it needs a large thermal reserve in the tank to compensate for the gap between production and usage. The legal limit for a shower in the United States is 2.5 gpm (gallons per minute), although you might have a higher flow rate if you are using an older showerhead or someone removed your flow restrictors for a high pressure shower (this article describes how it is done, so it should help you check to see if the restrictors are in place in your shower).

If your shower is running at 2.5 gpm and your water source is 40 - 50 degrees (meaning 60 degrees increase is required to boost the temperature to over 100 degrees), you need a heater with a minimum 75,000 BTU/hour to keep up with demand, according to this handy calculator. If you are using a shower that produces 4 gpm, you will need 120,000 BTU/hour to keep up. So if your pressure is more than you need, one solution to hot water capacity is to reduce the water usage using a reduced flow shower head.

Most people are looking for more pressure, not less, so this probably isn't a practical solution. Another option is to add a tankless hot water heater to one of the showers. You can also add a storage tank (e.g., SuperStor) to an existing hot water heater for less than buying a new higher capacity hot water heater. However, before upgrading the hot water system, there is a simple solution for getting the most out of the heater that many people overlook: turn up the temperature on the heater.

We have a 80 gallon gas fired heater. We can take an unlimited number of showers without running out of hot water. However, when we first moved into the house, we had the same problem. The water temperature on the heater was set to the minimum. After I turned up the heat to the maximum we problem went away completely. This is for two reasons that are mutally reinforcing:

1) If the temperature is set higher you will need less hot water to mix in with the cold (e.g., 170 degrees hot + 40 degrees cold mixed 50%/50% = 105 degrees, whereas 120 degrees hot + 40 degrees cold must be 80% hot water to get 104 degrees).

2) If the tank can't keep up with your usage, it has a bigger head start if the temperature is set higher. As the cold water refills the hot water tank, the tank temperature falls, and when it is below the 100 degrees, the shower will no longer feel hot, even with the cold turned off. So if your temperature is set to 120, when 20% is depleted, the tank water drops to 104 degrees. If the temperature is set to 170 degrees, the temperature will not cross the 100 degrees threshold until more than half the water is depleted. This is an oversimplification because even as the heater is falling behind, the heater slows the rate of temperature decrease - this static temperature mix calculation does not reflect the heating done during the decline. However, it is also follows that the tank will have more time to raise the temperature when it has until 50% depletion instead of 20% depletion.

There are several drawbacks to increasing the temperature of the heater, but they are not dealbreakers to me:

1) Heat loss from the tank to the surrounding room is greater, but modern tanks are very well insulated so this is less of an issue than older tanks. Also, my hot water heater is in my basement, so the heat loss warms the unheated basement a little.

2) You can scald yourself on the tap water, but everyone gets used to it so really you just have to warn guests. If you are concerned, you can try turning up the water in increments to give everyone time to get used to it.

3) If you have hard water, the minerals come out of solution more, so you might need a water softener. If you have hard water, you should get a softener anyway, because your pipes, valves, and showerheads will fill with minerals over time which is very difficult to fix.

So while not high tech, it is technology (definition: applied science) that we appreciate every morning.

One Laptop per Child

I gave each of my children their own laptop. It started with old laptops that my wife and I outgrew (a Toshiba Tecra 8100 and a Dell D600), but these same models are available inexpensively on eBay. The 8100 usually goes for about $100, depending upon the specs. The D600 usually can be found for $250 if you are patient.

We have standardized on these two models for the same reasons companies standardize - it makes it easier to service and support them. This way I can stock extra power supplies and other spare parts, and if two were to fail I can probably combine them into one working machine. You can also learn the quirks of the machines so you know what it will take to restore an imperfect unit. For example, the Tecra's often are listed with 128MB of RAM, because they frequently have one of the DIMM slots fail if the unit overheats from blocking the cooling vents for an extended period of time. 128MB of RAM is just not enough for most things, but you can buy a single 256MB DIMM for $40, and then the unit is perfectly usable again. Also the backlight inverter often works itself loose or fails, and this is a 3 minute repair using a $10 - $20 part, and you used to be able to get it done for free by Toshiba due to a recall.


We use a Windows 2003 Server for domain controller, Microsoft Exchange server, and file server. Everyone gets their own user account, but I have the system log them in to their laptops automatically. This really helped when they were younger and couldn't be relied on to navigate the "Ctrl-Alt-Del" windows login and remember passwords. To do this, you use the registry editor to change settings in the following group:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon

1. Set "AutoAdminLogon" to 1
2. Set "DefaultUserName" to the user name
3. Set "DefaultDomainName" to the windows login domain name
4. Set "DefaultPassword" to the user password

I use Windows XP on all the laptops, which works fine with 256MB of RAM. These settings also work for Windows 2000.

The first software I put on the laptops was FasttMath by Tom Snyder Productions. This program is basically math fact flash cards for the PC. It is well worth it because it keeps track of their progress, provides fact memorization games to keep them interested, and provides status reports for you to monitor their progress. It is mostly used in schools, but they will sell single copies to consumers directly. I highly recommend it.

The next software I installed was SafeEyes a content filtering program that runs on the laptop. I have mixed feeling about this software because it does effectively block content, but the number of times I had to manually reconnect the software was an excessive drain on sysdadmin support hours. It may be because all of the computers I put the software on also used wireless connections, which maybe confuses SafeEyes as the connections come and go. If you are using wired connections or if you're not worried about manually reconnecting it from time to time, you should check out the 30 day free trial.

Aside from content filters, you can create a whitelist of sites on a computer by disabling DNS and putting only the sites you want to allow in the local hosts lookup file. On Windows XP, this can be found in C:\WINDOWS\system32\drivers\etc\hosts. You could put entries in the hosts file like this:

165.193.130.178 http://www.funbrain.com/ funbrain
199.181.132.250 http://www.disney.com/ disney
209.9.8.79 http://www.webkinz.com/ webkinz
77.73.32.120 http://www.miniclip.com/ miniclip
208.139.194.177 http://www.starfall.com/ starfall

The problem with creating a whitelist is that the IP addresses can change, or there can be more than one ip address that is used for load balancing and failover of the site. But this is a low tech solution that can protect the innocent, but kids who are older and motivated to find a way around it can easily do so.

Aside from web browsing and FasttMath, the most common things they use the laptops for are drawing in Paintshop Pro, writing homework in Micrososoft Word, browsing family photos, watching movies (family or commercial), and loading up their iPods with my mp3 collection. My sons also have the Timex Ironman Datalink watch which can synchronize appointments, contacts, and notes with Microsoft Outlook. All of them are strangely obsessed with Google maps from time to time, but then again, isn't everybody?

Scamming the Scammers - an eBay Rant

I have to admit that sometimes I get taken on eBay. The great thing about eBay is that if you are a smart buyer it all works out in the end for you anyway. I have probably spent about $25,000 on eBay over the years, and never lost money. In previous posts I discussed the VOIP equipment, the home theater PC, and Tivo upgrade gear that I bought on eBay.

On three occasions I did have to take the time to file disputes and follow through on the resolution process. When I buy on eBay I have learned to take the time to detect obvious red flags and move on. In particular, I avoid:

• Sellers who don't take Paypal
  
• Sellers outside the US (possibly Australia, Canada or UK for unique items)
  
• Feedback scores lower than 100
  
• Feedback positive % lower than 98%
  
• Feedback that doesn't pass the smell test: all recent, all feedback on very low dollar items, lots of feedback from the same person, lots of feedback that sounds like it was written by the same person, etc.

But that isn't always enough. Once I bought an Emeco bar stool on eBay and received a very cheap knockoff. After the due diligence with paypal I received my refund, and Emeco gave me a great discount on the real thing when I told them my story. By alerting them to someone who was pirating the Emeco brand, I did them a service and they happily returned the favor.

Always pay by Paypal. If a seller doesn't take Paypal, it is because they don't want to be bound by Paypal buyer protection rules, which is either cluelessness, a sign of bad history with chargebacks, or a potential scam. All of these reasons signal a seller that you should avoid. Please don't ever wire money, send a check, or give your credit card details to anyone on eBay. Also do not ever send someone money after they send it back to you. This is a confidence trick - they send money back to get you to trust them so that you send a paypal direct transfer (which doesn't carry buyer protection), or another payment mechanism you wouldn't ordinarily use.

Be mindful of the 30 day deadline for disputing a transaction in Paypal. Some sellers will try to trick you into waiting past the 30 day window, so file a dispute as soon as day 29 arrives if you don't have your item yet, no matter how nice the seller sounds. You can always close the dispute later if the seller delivers, without much time or trouble to either you or the seller. Don't feel guilty; the seller doesn't deserve your money yet if you still don't have the product 30 days after paying for it. If the seller complains, tell them you will close the dispute and leave positive feedback as soon as you receive your item.

Take notice of the Paypal protection threshold, it can be either $200 or $2000, depending upon the seller. The eBay listing will show the level of protection under the payment section. The $2000 threshold is only offered for sellers with established positive feedback and verified Paypal seller accounts.

I would also encourage you to fund paypal using your credit card instead of a checking account debit if you are unsure you will be able to file a dispute within the required 30 days or if the amount of the transaction exceeds the Paypal protection threshold. If Paypal won't give you your money back, you can take it up with your credit card company and get the charges reversed.

Always ask questions if a listing is ambiguous, even if you think it is obvious, because it may be left unsaid to mislead you. For example, accessories you "know" come with something probably will not be supplied if the listing doesn't mention them. When a seller wants you to know the item is complete as shipped from the manufacturer, they usually say "factory sealed" or "NIB" (meaning new in box). When a seller says they are unable to test something, it probably means it doesn't work but they're hoping you will take a chance on it.

Always ask your questions on eBay using the "ask the seller a question" link so that you have proof of their answers, since direct email doesn't leave an audit trail that eBay or Paypal can rely on. Even if you are buying something "as is", the statements they make in the listing or in response to your questions must be true, thereby limiting the scope of the "as is" disclaimer. If the seller doesn't answer your question, this is a bad sign and you should not bid at all.

Just this week I was defrauded by a seller offering Adobe Creative Suite 3 Master Collection. The seller said they hadn't registered the software in response to my question, they accepted Paypal, and had positive feedback. It was a great deal, and I bought it.

After I paid, I noticed they had a different name on their emails than the name on the Paypal statement. This raised my suspicions, but could be innocent. Next, I saw the originating city on the Federal Express tracking screen was different than their eBay user information. While this could also be explainable, it raised my suspicions still further. After that my suspicions were confirmed when the seller wrote to me and said "I am having trouble with my Paypal account (I really wish there were an alternative to it!) So I am going to issue you a refund. Once I do, could you resend payment to name.changed@mailnull.com?" The mailnull is a nice touch, because it is a mail forwarding service, being used by the seller to try to cover their tracks.

Now that I knew the seller was a fraud, I decided to get the refund by playing along. This way neither Paypal nor I would have any inconvenience in recovering the money. "Sure, I don't see why not" I replied. Later I wrote back to say I hadn't sent the money yet because I didn't see the refund process on Paypal yet. In the meantime, the package arrived and the CDs were clearly bootleg. I called Adobe with the serial number, and they confirmed it was an invalid serial number.

The seller refunded the money on Paypal and sent a Paypal payment request. As soon as I confirmed the refund, I alerted eBay, Paypal, and Adobe. I never even tried to install the software; I just sent the disks to Adobe as evidence in the case their anti-piracy department is pursuing against the seller.

Amazon to the Rescue

This weekend, my father came to visit us in Massachusetts from New York. We spent hours playing Rock Band for the PS3. Rock Band combines singing, guitar, and drums into a great musical game. The karaoke and drum pad are my favorite because they are a more realistic approximation of actually performing. The guitar is more abstract since buttons take the place of strings. I wish Nyko or another after-market guitar controller company would create a real electric guitar for Rock Band, I would easily pay $200 for it.

I learned how to play acoustic guitar a long time ago, and I have been hoping one of the children would develop and interest in guitar and we could play together. Rock Band looks like it is helping them develop the interest, because they can better visualize the payoff. Let's face it, most people start playing as a teenager because they start going to concerts and want to be a part of the music, but younger children often just see practice as a time when everyone wants to leave the room :-)

Another great stepping stone is http://www.ivideosongs.com/ where you can watch free instructional videos on how to play guitar, and there is a large library of paid content for videos with either instructors, and in some cases the original artists who performed the song. Alex Lifeson has a video on how to play the guitar part of Rush's "The Spirit of the Radio", and John Oates shows you how to play "She's Gone". They also have videos for drums and piano.

The videos and the PS3 can be played on my Samsung LNT5271F 52" LCD HDTV, that I bought from Amazon last month. The family room in my house is getting heavier use these days, partially due to the social gaming and music enjoyment. Which brings me to my Amazon rescue story.

When I bought the TV in December, and I debated whether to buy it from Amazon or Circuit City. This hesitation was not typical, because I buy almost everything from either Amazon or eBay. It's just that for such a large purchase, there is some comfort in a local store.

For one thing, I was debating whether to buy the 120Hz model or the 60Hz model, since there is a significant price difference between the two. I was excited by the 120Hz, because my eyes resolve changes very quickly, and sometimes video motion looks stuttered to me, or I notice lights flickering when other people don't.

So I thought I should take a trip to Circuit City and compare the two side by side to decide which one to get, but since I wanted to buy it in time for Christmas, I would have to buy it there. When I noticed Amazon selling the 120Hz for less than Circuit City sold the 60Hz, I decided to read about the experiences other people had with Amazon in buying HDTVs. While there were some negative stories, they mostly concerned items damaged in shipping and the delays with getting a new one. In all, Amazon handled things well, so I was ready to take the plunge.

The low point of my weekend was when I noticed three large strips of bad pixels in the middle of the screen, which is $2500 worth of disappointment. These are over an inch long each, so definitely not something I could live with. So I wrote an email to Amazon customer service yesterday, and received an email today telling me to work with Samsung, and to contact Amazon if Samsung didn't make things right. I expect this is a stock response due to the number of times people call about one bad pixel, which is not considered a defect by some manufacturers.

I prefer working with retailers over manufacturers, so I decided to call Amazon customer service to accelerate the process. The customer service representative listened to what I had to say and scheduled the delivery of a new TV. So in a week or two a new one will be dropped off, and they will remove the old one. I couldn't believe it - they have made exchanging a defective HDTV even easier than at the local electronics store. They have raised the bar for value and service. Thanks Amazon.

MP3 in the House

A few years ago, I converted all of our CDs to 320kbps MP3 files. I considered using a lossless codec instead of 320kpbs, but I read about a very interesting blind test where 256Kbps MP3 files could not be discerned from the original CDs. What made this study special was not the number of participants but the fact that they were sound engineers from famous music studios, symphonies, and hifi manufacturers. So I bumped up the sampling rate to 320Kbps, just to be sure since I didn't want to rip 1000 CDs twice. I also decided to use constant bit rate (CBR) instead of variable bit rate (VBR), because the greater compatibility of CBR was more important to me than saving disk space.

We have more laptops than people in my house, so I set them all up on the kitchen counter, and the ripping went pretty quickly. By the time I loaded the CD into the last one, the first one ejected because it was finished.

The next decision was the best way to playback the music. First I connected one of my old laptops to the stereo using the line out from the laptop to the line-in of the receiver. The music collection is over 80GB, so the old laptop didn't have enough disk space, so I tried to store all the files on my file server, and connect to the file server over the wireless network.

Unfortunately the wireless network was just too unreliable for long stretches of listening to music, and there was no easy way to install a wired network to the audio cabinet. Larger hard drives are pretty cheap though, so I upgraded the laptop for less than $100 and stored the entire collection locally. The sound was picking up obvious interference, so I added a PCMCIA soundcard with optical output to the laptop (Creative Sound Blaster Audigy 2 ZS Notebook sound card). This completely eliminated the interference problem that was caused by either the cheap DAC in the laptop or the interference picked up by the line-level signal on the way to the amplifier.

For portable music players, the 320Kbps is a bit much, so I downloaded Easy CD-DA Extractor from download.com to run as a batch to down sample the music to 160Kbps. I have to admit ignorance of the inner workings of the MP3 algorithm, but in most codecs downsampling by a factor of two produces a cleaner result than fractional downsampling.

Now that I am in a house with a wired network, I am using the Playstation 3 as the MP3 library interface instead of the laptop. The PS3 connects to the server, which uses Windows Media Player 11 music sharing to send the music on demand over the wired network, and the HDTV is the interface for selecting the music instead of the laptop on top of the audio system. The ease of use, the HDTV interface, the wireless controllers, and quality audio make for the perfect setup.

The next challenge was to get the audio to the speakers in the ceiling. The new house had five pairs of speakers in the ceilings on the first floor, with a Niles VCS100R volume control in each room. I decided I could avoid buying a new piece of audio gear since my Model 7700 7-channel Balanced Amplifier has 7 channels and I only use 5 channels for my surround system (Axiom 4 x M80, 1 x VP150 v2, 1 x EP500 v2) in the living room.

The speakers in the ceiling are 8 ohms, and the amp can easily drive 4 ohms (it is designed to work at 2 ohms for head room according to the engineers at Outlaw Audio). However, when you attach five 8 ohm speakers in parallel to a single channel, you are left with a 1.6 ohm load, which would kill the amp. The VCS100R volume controls have a switch to double (or more) the impedence, which makes the load 3.2 ohms - well within the capabilities of the amplifier.

If you are connecting ceiling speakers, the heavy gauge wire required for the long runs won't fit in an off the shelf solution like the Niles VCS HUB8. I used two six-speaker wall plates in a 4 gang j-box to connect the heavy gauge wire together in a parallel circuit (you could also use one larger unit like the Niles HTP-7.1 ). The binding posts can be be jumped together on the rear using stripped speaker wire, and all of the speakers can be connected to the binding posts on the front, along with the 2 pairs that connect to the 2 amp channels.

The ceiling speakers are configured as a second zone in the receiver ( Model 990 Preamp/Processor ), so they can either play the same thing as the living room, or they can play music while the sound system in the living room is used for watching a movie.

Now we've got MP3 in the house.

Tivo for HD using Comcast

I started using Tivo when it first came out, but when I upgraded to HDTV, I couldn't imagine spending the $700 for the Series 3 at that time. So I decided to use the Comcast HD DVR purely because of the cost. It couldn't compare to the Tivo, but it was HD and it didn't cost anything up front. Eventually the limited space, terrible lag time on the user interface, and general lack of features was too much to tolerate, so I started looking for another solution.

Next I setup a PC with MythTV, the opensource DVR software, using the Mythdora distribution for Redhat linux. Mythdora is an excellent distribution, and makes trying MythTV pretty painless (like Trixbox for Asterisk). Unfortunately MythTV itself is not so easy to use, and there is a fatal flaw: the cable interface adapters such as the pcHDTV 5500 card can only tune unencrypted QAM256 signals, whereas Comcast was encrypting almost everything except channels available over the air. The firewire port on the Comcast Cable boxes also had 5C encryption, so I couldn't get premium content that way either.

As I looked for ways to capture HDMI, decrypt QAM256, or Cablecard tuners, I realized these were either too expensive or not yet tackled by the opensource community. While researching these options, the Tivo HD came out, which is a far better deal than the Tivo Series 3. I paid $250 each for them, and they have two cablecard slots, so you can use either 1 Multistream cablecard (a.k.a. M-Cards) or 2 Singlestream cablecards (a.k.a., S-Cards). Get the M-Cards if you can, because you pay a service charge per card per month.

Unlike the Comcast DVR, you own the Tivo, so you can easily upgrade Tivo to 1TB disk storage using WinMFS. With two Tivos (with 4 tuners total and a total of 2TB of storage) I can record thousands of hours of SDTV or hundreds of hours of HDTV on four different channels at the same time. On my older SD video Tivos, I can use the Tivo multi-room-viewing (MRV) transfers and thereby get rid of all of my cable boxes, which saves me the box rental fee each month. There are service fees for the Tivos, but I am happy to pay Tivo for a service that is vastly superior and costs less. I don't have video on demand anymore, but I can get on-demand content over my broadband connection from Tivo partners, like Amazon unbox or Jaman.

The most difficult part was getting the Cablecards installed in the Tivo. The first thing that caused difficulty was I hadn't unboxed my Tivos before Comcast arrived, so I didn't have the most up to date version of the Tivo software, and you need it. Then I could only get the OTA channels because the cards weren't properly paired (For MCards, Val: ? is displayed on the Cablecard pairing screen on the Tivo) with the head end servers at Comcast. There are some great support articles in the Tivo knowledge base, so I would be sure to print them for your installer. In particular, I recommend this article: http://tivosupport2.instancy.com/TiVoCollection/f8f40dc6-5fb6-4ed8-ac41-d8cd0d5c0824/ins_Content.html

There are a few myths you might hear from the cable company that you should be aware of:

1: "I can't hit your box, it will damage your Tivo" - completely untrue. There are three different kinds of signals your cable company can send to a cable box or cable card and the Tivo is fine with all three.

2: "Your system is fine, don't worry that it isn't receiving any channels, it will take a few hours for the channels to come in." It might take time for the program guide to appear, but the channels should tune right away, don't let your installer out the door telling you this.

3: "We don't support Tivo." Cable companies have to support Tivo and other cablecard devices. If you get this from a stubborn customer service rep, remind them they are supporting the cablecard, not the Tivo, and while it may be inconvenient, the FCC requires this.

When you schedule the appointment, you should ask for someone with cablecard and Tivo experience. Tell them to write it in the notes for your appointment. And if you live in the Boston metrowest area, ask for Rob Wheeler, he is the best contractor they have.