They run!

If the video wasn't taken with a cellphone, you would be able to see the coils pretty clearly while it's spinning.

Anyways, the new hubcaps are all on the motors.They all work as they should now. Unfortunately, due to USLI with the MIT Rocket Team, DBF (oh, and classes...) demanding massive time commitments, this project has slowed wayyy down. It's very unfortunate, but that's life: never enough time to do everything you want to do.

Pics:

Coils!!

The test rig setup.

That's all for now. I'll try to get more of it finished for the energy showcase coming up, but no guarantees.

Pics!

Damn my internet...typed up this entire post and lost it all. I'm not going to rewrite it all.

I finally sucked it up and rebuilt the eXKateCD (see previous posts for its story of misfortune). It has a Kelly KDS Controller, 9 new Lipos, wired hand throttle, and a KEYED battery selector that should prevent anyone we don't want from turning it on or plugging the battery in backwards. Check it out:

The KDS controller

The new LiPo array.

As it turns out, the KDS series of Kelly Controllers doesn't have Regenerative Braking, even though it is perfectly capable of doing regen. They just didn't include it in the software so they could charge twice as much for the series with regen....or they are so incompetent that they didn't realize they could easily make it do regen. Either way, the board doesn't have brakes, which is bad. A new motor controller will be designed/built for it (probably not by me considering all the other stuff I'm working on) that'll have wireless control via Xbee radio modules.




ELB Pics:
I thought I had more pics than this, but I couldn't find them.

Right: outer-side hubcap with polycarbonate inserts after 3000 grit lapping paste. Left: The same as right, but after heat treated with a heat gun. This melted the surface of the plastic, leaving it crystal clear.

Pile of crap inferior, busted polycarbonate hubcaps.

Update: The motors are all but completed. Just waiting on more screws to come in from McMaster. I hope I didn't damage anything when taking them apart. One thing I did learn when taking them apart pertains to ball bearings. When designing an assembly with ball bearings, make sure to only have the bearing press-fit into one side of the assembly if the assembly is ever to be taken apart. Furthermore, make the press-fit the part of the assembly you want. Sounds obvious, but I never had to think about it before this. Two of the 2" bearings were semi-press fit onto the hub-shafts, making it impossible to get them off, thus making it impossible to press-fit them into the hubcaps. So I had to take the hubcaps to the machine shop and take a few thousandths off the bearing surface to make them a close fit instead of a press fit. Of course, none of this would have happened if I had just gone with aluminum hubcaps in the first place...

To-Do list:
1. Glue tires onto wheels (2 hours)
2. Component layout inside of battery box (8 hours)
3. Figure out trucks risers (1 hour)
4. Make hand-held remote control (2 hours)
5. Program motor controllers to take throttle commands from hand-held remote control (2 hours)
6. Test (1 hour)
7. LED lights (4 hours)
8. Waterproof / Loctite (1 hour)

I'd say this project is 80-85% complete at this point. But with DBF, Rocket Team, and classes in full swing, the last little bit might take awhile.

News

Latest Lesson learned:
Designing something that might work is significantly easier than building something that will work.

In other news:
I co-authored with Shane and Charles a paper that was accepted to the EVER '11 conference in Monaco!!!!!!!!!!

In other other news:
We got the 4th motor calibrated for ELB finally, after I replaced the sensors. Still no idea what was wrong with them. Anyways, this means I can start replacing hubcaps and finally finishing the motors. I'll have some pics of stuff when I find my microSD to SD card adapter.

That's all for now.

Back

Back in Cambridge. List of stuff I need to get done:

1. Fix sensors and calibrate motor 4
2. Finish the layout design of the battery box
3. Place all components
4. Waterproofing
5. Make handheld controller
6. etc...

Still a lot left to do. This month is the 1 year anniversary of the beginning of this project. It shoulda been done 6 months ago, but I've been too busy and have had too many setbacks. Oh well.

Crap

We got three out of four hub motors calibrated, which is awesome. The current problem is that the fourth hub motor's sensors decided to die...no idea why or how, because they sometimes work, and sometimes not. It can't be a magnetic field issue because a. they are mounted in the exact same locations on all motors. b. they do change state...except sometimes to the WRONG state. WTF, that shouldn't even be possible. I even tested them with a small magnet and an oscilloscope before assembling the motor, and they worked fine. And we determined it wasn't a problem with the MC board because we ran a different hub motor on it just fine. Oh well. I've ripped the sensors out and am going to put three new ones in at some point. Then reassemble and test again. Then put NEW HUBCAPS on! Wohoo.

Lessons learned over the past month or so:
1. Sensors can fail even when taking every precaution
2. Don't use steel alignment pins (see earlier posts) until the final motor integration onto the board. Pulling those things out sucks
3. Make your hub motor rotors with a water-jet, like this.
4. I should have wound the motors hotter (or just made smaller motors). At 10A, I'll have more torque than I could ever use/stay on the board with. In fact, this board would have no trouble at all running on two motors. Something I will consider if weight ends up being an issue.

Mid-November

I'll know I'm doing too much stuff when these posts start coming at more than 1 month intervals.

Anyways, time for another ELB update!
I finished cutting and rough sanding the last 40 polycarbonate inserts for my new hubcaps.

It's INCREDIBLY tedious work to polish these things. The above is after cutting, 220 grit, and 400 grit. There's still 600, 1200, 1500, and 3000 (lapping paste) to go. Anyways, this is the point where I got bored and decided to work on something else.

This is my charger: Turnigy 4x6S . It can charge four 6S packs independently. I figured I could use it to charge my 12S ELB pack (just link two of the ports together). But...
Each charging port is NOT independent, despite what you may have heard about it, or may assume about it, or read about in the description ("All ports work independently of each other."). From the outside, all you see is a single input for 12Vish DC and 4 charging ports. Internally, there are 4 separate chargers. Sounds ok, right? However, all of the chargers' inputs (+ and - ) are linked by traces that go all the way around the board. This wouldn't be a problem if they were high quality (isolated input/output) chargers. But this is a Chinese Cheap Charger (CCC). The negative/ground wire is connected straight through from the input to the output (battery ground). This means that all of the outputs are at the same potential, which in turn means you can't link ports and charge anything over 6S. I need 12S. There goes $100. OR:

Doctorbass to the rescue. Check out his hack for this charger...genius. He made it into a single 24S charger by isolating the four chargers by cutting the traces that link them, and then buying 4 small (cheap) switching power supplies, 1 for each charger. His application is a little different than mine, so he did some other cool modifications, but I'll just show how I did it.

Take it apart

Each charger has two holes like this for wires to go into. It's like they were originally going to manufacture it to run off of four independent power supplies (like it should have been), but they instead just added a trace all they way around to save money.

Cut traces on each side of each set of input holes. Dremel worked well.

Cut the bottom traces, too. Be careful not to cut into other traces, just the power traces.

Back side was easier. Could just slit the board without hitting any components.

The four 12V, 5A power supplies. You can get these on eBay for <$40.

Cut the DC plug off the power supplies and string the wires through the wire hole in top plate of the charger. (De-solder the existing input wires first.)

Solder the new inputs to the circuit board.

Yep, definitely isolated now.

Finish soldering all the input wires. Route them as you see fit.

Semi-finished. They all work!

Removed excess wire. That's better.

Double-stick tape/duct tape the power supplies together. I velcroed the charger to the power supplies, too.

Now I have one big block of a 24S, 200W charger. Not too bad for $130 and 2 hours.


In addition to these things, Shane's been helping me calibrate the motor controllers to my motors (well, he's been doing most of it).

Note the old hubcaps with chunks of missing polycarbonate....why I'm making new ones.

I've got updated data for the motors now, too. Before, using a Turnigy controller and running the motors sensorless, we calculated a top speed of about 30mph. Now, using sensored sinusoidal control and about 15 degree advanced timing, the top speed is around 20mph. Not too bad. The really impressive thing is the torque. I'm looking at getting 50lbs of force at the ground..assuming 200lbs of mass (rider+board), that translates into 1/4G of acceleration, which is nuts...especially for something without a seat or handlebars. I probably should have wound the motors a little less for torque and a little more for speed (less windings, or thinner stator, etc), but I think 20mph is plenty. 



That's all for now.

The other Electric Longboard

Well, bad news for the other electric longboard (the one made during the Edgerton Center Summer 2010 Engineering and Design Class).

Remember the eXKateDB (drill battery) hack?:

I shoulda seen it coming, but see those little connectors? They can be plugged in backwards...yeah...bad stuff happened. Turns out the Exkate controller doesn't have reverse polarity protection. I actually found this out the hard way at the end of the class this summer. I plugged the battery in backwards and it fried some components. Luckily, Shane was there to help me fix it. This time (wasn't me) however, more things fried:

Blown up transistor and resistor. Another transistor is fried on the board.

You can see the diode we replaced before. It was fine, but the transistor below it wasn't too happy.

Assuming more stuff wasn't burnt, we probably could have fixed it, but the whole thing was turning into a hack at this point. So....new controller! Brushed Kelly Controller to be specific. It has better specs than the Exkate controller, for a lot less. However, it doesn't have a built in radio system. So....new radio system! A Hobbyking 2 channel 2.4GHz radio was purchased ($17). We'll have to figure out some way to translate the PWM servo signal to a 0-5VDC signal for the Kelly throttle input, but that shouldn't be too difficult. Hmm...what to do with the extra channel.

A new set of Lipos are here (I need to find time to install them :/ ). To prevent what ultimately caused all of this trouble in the first place, a keyed battery selector will also be added. After that, the longboard should pretty much be set and idiot-proof resistant.