Coming Soon – Drill Torture Tests

Just a sneak preview of an upcoming “project” at OMG… Member Ben found a great old drill at Habitat ReStore, and it spawned a conversation about torture testing various drills under extreme circumstances.  As a test, we pitted Ben’s drill against one of our cordless Ryobis… More “sciencey testing” to follow.

Remember, these sorts of things aren’t really planned or scheduled in advance; the best way to get involved is to show up a the space on our regular Tuesday meeting nights (along with off-week Thursdays, like tomorrow night).  Doors typically open around 5:30, and you’re invited!

Robots!

This past Tuesday, Jeff Jensen, a long time friend of OMG was at our regular meeting to get some help with mechanical assembly and soldering of a dozen CEENBoT units. Jeff is part of a program that develops the CEENBoT robots for education and the program has been so successful that Jeff is overloaded with requests for new robots, so several OMG members jumped in to help out.

We had several other visitors, including first-time guest Chris, who promptly jumped in to help out. This really embodies the spirit of OMG, creating an environment where folks feel comfortable getting involved in whatever’s going on.

Thanks to everyone who helped out on Tuesday!

Oscilloscope Music

A few weeks back, I caught a video on AvE’s YouTube channel of graphics drawn on an oscilloscope, given an audio input. Last week, Ben, Garrick and I decided to give it a try at OMG.

According to Garrick’s research earlier that week, “older scopes” do better with this sort of thing, and OMG’s scope is plenty old. We had to do some tinkering with the settings, and the phase, eventually arriving with the left channel on Input 2, alternating vertical and External trigger (ch2). It worked best if the laptop volume was turned clear up, as it gave the best signal to noise ratio.

We’d initially hooked the scope directly to a laptop headphone jack (through a spaghetti of cables), but as Eric pointed out “To be music, there’s gotta be…music”, and no devices we had would play on the headphone jack AND the internal speakers at the same time.  We ended up hacking up a powered speaker to give us a stereo output and play both channels on a single speaker. This gives us something to feed the oscilloscope AND lets folks hear what the audio actually sounds like. In addition, it had a lot less noise than our initial mess of wires.

As for what we played, we just searched YouTube for “Oscilloscope Music”.  Someone who works with Jeff mentioned Aphex twins “windowlicker” and “songs about my cat” by Venetian Snares as two examples of spectrographic songs.

Founding Day 2017 – OMG’s 7th Anniversary!

We’re going to be celebrating the Omaha Maker Group’s 7th anniversary on Tuesday, August 29th. As has become our custom, the evening will include dinner, dessert and the awarding of the annual Founders’ Prize. In addition, I’ve dug up some photos from long ago, showing not only the old space, but also our current K Street space as it was when we first moved in.

Dinner starts around 6, meeting and awards at 7, and dessert thereafter. Additionally, we’ve come up with a few interesting things for a raffle, so we’ll be drawing for that after dessert. Still TBD, but there might be a special “show and tell” after dark… I still need to check with Garrick for details though 🙂

This is an “open house”-type event, and members are encouraged to bring guests. It’s a great opportunity to invite your Maker-inclined friends, family and co-workers to see our new and improved space and find out what the Omaha Maker Group is all about.

Please RSVP below, indicating whether you’ll attend for dinner, dessert, both or neither. Since food needs to be ordered in advance, please be RSVP’d by August 25th so we have an accurate-ish headcount.

https://goo.gl/forms/vwAKXQjRkAGilReB2

Banker’s Box Storage Plans


For years, our makerspace has used a hodgepodge of solutions for storing members’ projects in progress and other personal belongings.  Most recently, we’ve used a dozen or so plastic totes.  The totes worked great, but were limited in quantity (they were industrial waste, and no more matching totes were available) so that not everyone could have one.  Additionally, these totes were slightly trapezoidal, which wasted quite a bit of space between them.

To that end, Ben and Kevin undertook a project to convert personal storage to standard Letter/Legal Banker’s Boxes, which are readily available and pack more densely.  They are a bit smaller than the totes we were using, but most members totes weren’t full, and we can store twice as many boxes in the same space.

Read on for full plans and assembly instructions.

Continue reading

2016 OMG Fir Lumber Rally

Here is everything you need to know for the 2016 OMG Fir Lumber Rally!
Date:  Tuesday, March 29th, 2016
Time:  Check-in starts at 7:00p (doors open by 5:30p for testing, tuning, and final preparations)
Who:  Open to all OMG members and their guests (family, friends, coworkers).
Mailing-list lurkers are welcome, too!
Cost:  $5 per registrant (up to 3 cars per registrant)
Where: 8410 K Street, Suite #5, Omaha, NE
There will be (2) classes of entry – Gravity and Gravity+.  _ALL_ entries MUST adhere to the following:
– Your vehicle MUST fit inside a “Go/NoGo” box – meaning it can be no longer than 7″ and no wider than 2-3/4″.  Also, because of some track improvements being made, it can be no higher than 10″.  For you scientific types, that’s 7.000″ long, 2.750″ wide, and 10.000″ high.
– Your vehicle must roll down the track, so it needs to have at least 1-3/4″ clear width between the wheels, and at least 1/4″ clearance on the underside.
– Your vehicle must weigh no more than 6.00 ounces – note that this is (1) ounce heavier than standard Boy Scout rules, so load ’em up!
– And that’s it!  You don’t _have_ to use the BSA-approved kits (although they are only $4 at places like Hobby Lobby), and you don’t even have to use wood.
Additional Rules for Gravity+ Entries:
– Your method of power must be reasonably safe when around other participants, unless you provide lead radiation suits to all participants
– The mass of your vehicle must be the same at the end of the race as it is at the beginning of the race.  Exactly the same.  Not kinda the same, or sorta the same.
– With one exception – if you can successfully produce a 6-ounce live steam-powered entry, consideration will be given if your ending mass is not the same.
– Your method of power cannot bring harm or damage to the judges, other entries, participants, or the track itself.
– You may want to consider some sort of nose/forward-mounted pressure switch to keep your vehicle “off” until the gate drops.  We would hate for your car to use up all it’s power sitting in the starting gate because of some sort of delay that might possibly happen.
– In order to earn points for your entry, it must cross the finish line ON THE TRACK. Just sayin’….
General Racing and Scoring Stuff:
– Participation is open to all ages.  Junior participants in each class will be ranked as a group, as well as being ranked with the class in general (we will identify juniors at registration)
– All cars must be registered before the start of the event. At this time, they will be checked to ensure they meet the specifications in the rules.
– Every vehicle will run at least twice (once on each lane), with the best score kept.
– To celebrate and promote the Maker spirit, there will be time bonuses for Creativity, Workmanship, and Whimsy. These bonuses will be voted on by the participants, with the top 2 vote-getters in each category receiving a time bonus deducted from their fastest time.
– To further promote the Maker spirit, there will be a time penalty for the Least Effort. This will also be voted on by the participants, with the vehicle deemed to have the least amount of effort put forth earning a time penalty added to its fastest time.
– Time bonuses and penalties will be determined prior to race day, and will be announced then. But, trust us, they will be worth their while.
Some Other Stuff:
– If you have a concern about the $5 entry fee, please see Eric or Dave K. We want as many people to participate, without barriers to entry
– Since so many folks participated in the first event, there are still excess of supplies like graphite, tuning mandrels, lead weights, etc. If you need something, just ask!
– The track will be setup at least a week prior to the race, for practice and tuning
– We will probably have at least one “Fir Lumber” Open Shop night prior to the race, so you can feel free to drop in and work on your car with everyone else.
Thank you Eric for the wonderful summary!

Vacuum Chamber

What happens when you give makers a vacuum pump and a bin full of components to rummage around in? Watch the videos to find out.

Can you think of something interesting to put in a vacuum chamber? Post in the comments below.

Battery Derating and Chemistry Comparison

This weekend, Dave K was asking me some questions about the performance of our sweet LiFePO4 battery packs for the power wheels cars. At the time I was only able to answer his questions in generalizations, so I decided to sit down and show exactly how our lithium compares to more conventional lead-acid.

We’re running a custom 32-volt pack, but we can calculate with a more convenient size and all the observations will be proportional. Conveniently, our new teal cells are designed to create a nearly drop-in replacement for an existing form factor of gel cell. This makes direct comparisons really easy. Both options are 20 Amp-hours and both have nominal 12v output, with true output being a volt or two above that. So, straight off the bat, you’ve got the same form factor and voltage, with one option weighing 14 lbs and the other option weighing 6.6 lbs. More than double the energy density.

However, there’s quite a bit more to it than that. The two battery types are rated differently and have very different internal resistance. The lead battery gets its rating at a 20-hour rate, and the lithium is designed around a 30-minute discharge. When you use either battery outside of its intended performance envelope, you wind up with something other than the nameplate rating. There’s a formula to estimate this effect, called Peukert’s Law.

Peukert’s Law uses the following equation:

Where “It” is the effective capacity of the battery, “C” is the rated capacity, “I” is the discharge current, “H” is the rated discharge time in hours, and “k” is a constant for each different battery chemistry. For lithium, k is approximately 1.01, and for gel cells it’s around 1.15.

Do the math, and you wind up with a chart like this:

Capacity

Bearing in mind we race with a 40 A fuse and occasionally burn one up, the benefit of lithium batteries in this application is pretty significant. We’re still getting more or less 20 Ah out of our packs, while the equivalent lead-acid would be derated to around 11 Ah. Suddenly we have 3.7 times the capacity per pound!

Beyond all this, there’s one other effect to bear in mind – voltage sag. When you load a battery heavily, some of the power is lost to internal resistance and you wind up with a lower output voltage than nominal. I don’t have the information to calculate this, but the effect is a lot more dramatic for lead than it is for lithium. We know from KITT that even during heavy use, we maintain close to 32 volts out of our pack until it’s almost completely flat. The “equivalent” gel-cell pack would produce at least a couple volts less in use, which means less total power is delivered to the motors.

In the end, our lithium batteries are giving us more than four times the total power of an equivalent weight in lead-acid. It’s also a lot easier to charge and maintain three battery packs than the dozen or so we would need to race two cars on gel cells. Surprisingly, even total purchase cost doesn’t look all that bad: Our total cost for the two packs on Project STEVE, including shipping, is $655. By comparison, 12 of those gel cells costs $454 and they’re so heavy that particular supplier won’t even ship them (but figure at least $100 in shipping from anyone who will). The only real disadvantage is that we’re carrying a larger portion of our $500 on-track budget in batteries and have less left for the rest of the car.

I think it’s worth it.