p0w3r Drive: Three Cheers for the Arbor Press

Expecting to do some research this afternoon; did not exactly pan out. So I elected to say on west campus and do some wheel work.

The other night I tried boring one of the 5" 30A durometer wheels..



... but then it exploded. Synopsis tells me there are air pockets in the core material, and my feed rate was too high, which caused the bit to grab and toss the wheel. 300 fine for aluminum, not so much for plastic

Today, I went for round two. Turned the lathe into high gear, 455 rpms and lots of non-cinnamon (unfortunately) Tap-Magic. Like magic, we now has a properly bore'd wheel.



Posing with the stator for comparison.



Speaking of which, I put the stator hub back on the lathe and reduced part of the center mass. This would make internal wire organization easier by allowing more internal wiggle room.

Decided to tackle the flats next. Unable to find the binding screw for the large Vertrax mill, I went over to the ME2110 labs to barrow their cute mini mills.

OH GOD THE STORIES ARE TRUE! These mills really suck. I was making passes through aluminum like a pro, when I realized the mill axis started drifting. I felt like a inverted pendulum balancing robot, constantly adjusting to changes in my environment.




Either way, I finished the task, and with a half decent finish as well. Next chance I get, I'm asking my fellow studio ULI's how to tighten the collets on the Vertrax.

While I added a roll pin groove using a hacksaw, I finished preparing the waterjet, post-dredging. I want to say it would take about an hour to fill the tank manually, but since I filled it over the span of two days, nobody remembers. Similar is to be said about the number of licks it takes to get to the center of a Tootsie Pop.

Waterjet filled, cutting commences. I cut the magnet ring laminations from a 1/4" plate of A-36 mild steel, end caps from 1/4" 6061 Aluminum, and the spacers from 1/8" polycarbonate.




Ironically, the material for the spacers was the sheet of polycarbonate that was stolen from me last semester. Hmmm, how circular.

There was drilling, tapping, countersinking, and a big hand from the enormous arbor press. I declare the hubmotor mechanically complete. That leaves us in this current state:





Gathering inspiration from Iron man 2, I proceeded to wind the motor. 23.5 turns of wire per tooth, dLRK style for space savings.

Lesson learned: If you wind with anything 20ga or lower, wear gloves or wrap cloth tape around your fingers. Your writing hand will thank me later.



Completed stator winding, terminated with a Wye connection. I'll wait to see if this motor actually works before adding the sensors. This means the possible run date is the 23rd of Feb, seeing as how UPS managed to butcher the shipping of the box of magnets (routing delays).

Until then, cheers.

p0w3r Drive: Turning

Late Friday night, looking to build. Waterjet is under its scheduled maintenance, so I elected to roll on over to the lathe for some quality turning time.

Feeling too frugal to purchase a large piece of Aluminum round, I pulled out a 1.25" dia round of 6061 from my scraps. Slightly less than 32mm. Shouldn't affect the system too much. I may add some anti-static tape to fill the gaps if necessary.



Post-Turn part. Drilled through with a 7/32" and tapped to 1/4-20. Chamfers with whatever degree I could find were made on outer edges. I was surprised to find a beautiful mirror-like sheen for the finish. Too bad that won't last long.



As illustrated in the model in a previous post, the ball bearing goes over that extrusion.



Radial picturage.

Next time when I finish prepping the waterjet, Ill cut the endcaps and the magnet can.

Speaking of magnet can, I elected to make a small design change in favor of using more (than one) of the 25ct bag of 2mm roll pins I bought. So here we have 7 additional 2mm holes through the magnet can rings as alignment devices.



I will probably partially press the rings together, add a gratuitous amount of superglue and press the entire assembly together. Should be solid. This part should NEVER BE SEPARATED!

Already I am beginning to find some slight design oversights. A 1/2" shaft with a 1/4-20 tap was a poor decision because that leaves very little room for wires to exit. Think of it as a 1/2" tube with 1/8" wall. My options are to make flats on three sides of the shaft or increase wire gauge. I am favoring the latter because cable organization would be far easier. I should be within reasonable current ratings in normal scenarios.

Hububububble Motor

The next logical step for any piece of technology is to make it lighter, more powerful, and smaller. These goals I hope to find in the first actual hub motor I will be building.

Don;t get me wrong, I have built my own brushless motors before. In fact, if anyone recalls the first Attrition, it had a custom built 40mm motor to internally spin the drum. Now it is time to build yet another motor, slimmer, larger in diameter, and torquier (new word or sp?).

First round will be a test platform. I have a bunch of ideas on improving the sea of hub motor designs but those will be applied once I can prove to myself that I can produce one basic device.



Borrowing the techniques of Shane Colton and Charles Guan, this motor will have the following characteristics:

1. Flux ring is composed of waterjet stacked laminations. It will feature internal grooves to make magnet housing easier.
   
2. Stator hub is a single piece turned aluminum round. It will have milled flats on both ends to facilitate the exit of motor and sensor wires.
   
3. The motor will have three hall effect sensors to interface with the controller
4. Motor will be wound 30-turns per tooth, dLRK for space savings
5. 5" OD, 1.5" wide
6. 70mm x 16mm Hitachi Stator
   

Where did I get these numbers from? Charles wrote up a neat instructable with will teach you motor building basics and some sample calculations for rough estimates. Very useful and highly recommended.

Instead of featuring threads to grip a tire, I will be using a "keyway" integrated into the flux ring.



In actuality, it is an extension of the through holes used to bolt the entire motor together. I sunk in the material where there were no screws, and left the extrusions as mechanical "grips" to grooves I will be adding to the inner diameter of the cored out 5" wheel. Forces are in the correct direction, I dont expect anything pushing the motor horizontally, this should work. The number of screws might change depending on how unsafe I feel about the sheer forces on 6-32 screws.


The pile of parts has already begun. McMaster-Carr arrived today, so I received two 30A durometer 5" wheels, three 1/2" bore ball bearings, and 2mm roll pins. I already salvaged the stator from an earlier grab, and the magnet wire recycled from previous orders. The bag of 6-32 flat screws came from Cake, where I ordered a bag of 50 only to use 2. Gotta love bulk buys.

The remainder of the parts should be coming in throughout the week/weekend. Speedy Metals is expected to arrive tomorrow, which means I can begin waterjet cutting the flux rings granted the machine is not broken (oh no my baby!). I suppose then it is possible to have a rotating wheel by Saturday morning. The Applied Magnetics order is projected to arrive Monday, but gluing magnets was never a time consuming issue since it is just adding glue. I don't need to be watching the grass to know that is growing.

For the time being, project name sits at "Power Drive", or "p0w3r Drive" if you are feeling creative.

Survey: Self-Balancing Electric Skateboard

Please help my team win the Inventure Prize by filling out this short survey. I promise it won't hurt!

The next prototype. Notice no hand controls, unexposed electronics, and simple design.

-22" long, 12" wide, 6" tall (wheel height)
-Weight reduced all metal frame for strength and durability while light enough to carry.
-Pneumatic wheels allow the user to silently and gently cruise over bumps and obstacles.
-Lithium Polymer batteries allow over an hour of run time with minimal weight
-Runs about 9 mph
-Rider Sense safety features prevent accidental injuries to self and others
-Customize your ride with a variety of interchangeable decks!

If you're completely unsure about prices, here are some related products:

$550- EMAD Electric Skateboard	$160- Razor E200 Electric Scooter
$190- Sector 9 Longboard	$6200- Segway i2 Personal Transporter
$300- Altered Wombat Electric Skateboard	$760- Altered Drop Electric Skateboard

Hot n Cold

By now I will be back at Tech. By now I should be starting to go to class. Instead I've been holed up in my residence because GT has shut down due to a flurry of snowfall last evening. It is pretty cold outside, but alas there is work to do: Cake's drive escs are getting too hot!

Seth at the Robot Marketplace recently informed me of a new set of KW motors for the B-series gearmotors. These guys pull more current, but are spec'd at 937 rpms at 12V or so. That is ~300 rpms over the old motors which will work great for my 1.5" drive wheels.

But if you ask me, it still feels slow compared to DDT. So lets take the motor mods a step further.

Tower Hobbies sells paired motors for direct drive foamies. 180 sized, high rpm, high current, and the correct shaft diameter. More importantly, they were on sale for a bulk buy!

The operation was a simple motor switch since the mounting patterns were the same.



Here the motors are installed with the B16 gearboxes. Ignore the new escs for the time being.
Months ago, I also purchased two scorpion mini escs to replace the damaged scorpion HX dual esc. You may recall, I had some SMT components fall off the board and while it has served me well my distrust is well placed. The two scorpion minis side by side fit perfectly horizontal in the electronics bay and open up much more room for the wires and plugs from the drum.



I applied a light application of glue on the edges to hold the two boards together, so that I could use breadboard jumper wires to bridge the main esc terminals like P0W3R busses.



Note how there are two plugs on the esc. One plug is actually for battery, but the other connects the the drum esc. Having the same connect with the same polarity makes for stupid proofing.

The real problem was that the new motors drew more current than the escs could handle. Evaluating my options, I felt that adding heatsinks was a far easier solution than disabling current limiting or upgrading the FETs. I cut some blocks of 1/8" thick copper bar (back when copper was not ass expensive) and tapped some 4-40 threads to facilitate mounting to the FETs.




A light application of silicon based heatsinking compound helps heat transfer between the materials. I also made a note to sand and polish the mating surfaces. Oxidation on the bar left lots of non-conduction crud on the outside.




Finally mounted we discover the robot to be significantly quicker, with extended runtime. I can achieve approximate 3 minutes of vigorous driving before the escs overtemp. This is acceptable.

Here is everything installed in the robot. The first picture of this post shows an unexpected benefit of adding the heatsinks. The board material fits right in between the header pins and the capacitor in my AR6110 receiver for optimal space savings!

Safety Razor Safety Advisory Report

So it's been a month since I butchered a child's Razor scooter and shoved a electric bike motor system into it. Let's hear some results!

I am able to use it for inter-campus transportation with about 50% capacity drain for a full day.



That's acceptable. Especially since it is probably mostly burst amps from accelerating. Voltage has yet to drop below nominal 22.2 (for a 6-cell lipoly). I still regularly monitor the pack for increased volume, but nothing vile has arisen. The picture above shows post-charge results. We have a 66% drain over an extended run time (I had group projects across campus that evening). You'll have to excuse my camera. No flash superimposed the words "END" and "BAL" to create the illusion of "BAD" on the LCD screen.

Over a period of time, I discovered my ground clearance to be steadily decreasing. My predictions have been reaffirmed. The amount of metal removed from the original frame, combined with the hastily designed frame extensions drastically reduced the integrity of the structure. I disassembled the frame this holiday break and discovered the fracture points to lay just as I had predicted: the region where aluminum and polycarbonate met.



All of this could have been avoided by starting with a single piece aluminum frame extension. Thankfully, I am still a ULI, and speedy metals is having a 10% holiday discount until January 31. Therefore, bring in the upgrades!



From the image, you can see the back end remains virtually the same. I rotated the motor mounting holes so that the centerline from the motor shaft to the wheel deadshaft were in line. Originally, the sprocket would rub against the spacer with left from some interestingly deep erosion marks as illustrated in the picture below. Undamaged spacer included for reference. I hope you know what a hex bolt is supposed to look like.



The majority of the changes were made to the front half. This iteration does away with the original scooter frame. It was far too troublesome modifying the frame to the design and it bore little fruit other than comedic value. This body is serious business. Slots and tabs everywhere. The accessible panel has been moved from the bottom to the top. This is because repeated ground scrapings sheered screw heads which made it a pain to disassemble. Speaking of bottom plates, a UHMW skid bar will be added to take the blunt of aggressive gutters and sidewalk ramps. On top of all that aluminum will most likely be a sheet of 1/16" garolite. Just something to cover the large gaping service channel and be pretty. If it is garo, I might even consider laser engraving a graphic into the center of the deck. Gettin' fancy now...

Of course, this frees up about 2-3" of space in the scooter body, not to mention the extended width and height. This means I can opt for a BIGGER BATTERY or protection to my current pack. Both would be nice, but I may push for the larger battery in preparation for the next advancement in campus transportation: MTD (to be described in detail later).

Lots of great material coming up (but its late, and im lazy).
-BBots
-MTD
-Hardbord

I Added a Scooter to my Motor

Here's the story:

On Black Friday, I bought this Razor-A scooter for $17. Now why would I waste my money on a scooter built for 5 year-olds(+)?

So I could concatenate one of these with it:

That is a 24v, 400W Kollmorgen brushless sensored motor that weighs 5-6 lbs. It is made for electric bicycles and weighs more than the scooter frame. Finally, it is larger in diameter (~5") than the scooter wheels (98mm ~ 4").

Needless to say, this is a project of epic disproportions! Yet, I still want to be manageable so I can actually use it in my cross campus commutes. Here's the game plan:

I am going to make an extended under body to house the batteries and extend the length so I can have some foot space and motor mounting provisions. Tentative model:



The wheel will be chain driven (#25) at about a 2:1 ratio. The frame thickness about the body is 1.25". The spoiler on the back is not for down force but rather acts as a foot rest because the frame is so small (seriously, the frame can only fit one of my feet lengthwise). Everything has slots, T-nuts, and delicious waterjetting. This will require major frame modifications too. The rectangular extruded frame will need to be cut on the bottom to allow the battery to hide inside. Also, some of the flanges on the side will need to be cut off because I need a flat surface to bolt the aluminum plates. Each operation removes from the structural rigidity of the frame which worries me.

Now one decision I am regretting is making the front segment from 1/4" polycarbonate. Why on earth would I make such an important part from (thin) plastic? Well because I already had it on hand. I'm in college and money doesn't grow in trees. I am worried about it bending or snapping somewhere in that region. I would run FEA on the part, but I have no idea what grade of shit-luminum Razor uses on their scooter.


Lots of pretty parts. The front of the undercarriage is made already from pre-existing plates of polycarb. Longpack and Macromotor wait in the wings...


And here is the integrand. One razor scooter awaiting cosmetic surgery...

Anyway, A lot of building happened in the span of three days and magically the project is done! My phone actually ran out of batteries so I couldn't take any build pictures. :(

Sorry folks, all you get are end result pics and video!


Sitting pretty by my fridge(s).


The throttle is a 5k pot with a shaft hub from Servo City. I should enclose those wires sometime soon.


The rear module. You can tell it is slightly different from the original CAD because I had forgotten which direction the motor spun. This made for a very disappointing initial ride test.


Closeup of the slot and tab T-Nut design. I experimented with the tool offsets on the waterjet such that it is a perfect slide with higher quality cuts. Are you proud of me Charles?


The underside. Notice where the metal becomes polycarb. I expect this region to be first to fail because it sits in between the two wheels and theoretically supports the entire rider's weight.

It has more than enough power to flip a rider over and reaches a top speed of ~20mph (calculated as 3500rpm on a 98mm wheel). It is amazingly unsafe...

... so I shall call it, "Safety Razor"