Monday, June 26, 2017

DISASSEMBLING MOTORS, TINY BIKES, AND A SHAFT


Hello again! Project directions have shifted quite drastically since last post. While compiling the bill of materials for Tee-mobile, it became clear that this was going to be an expensive endeavor.

Cost of raw materials sans motor, wheels, controller, batteries..

Luckily, the quest for a fast thing didn't end there. Last summer, I wound up with one of these babies:


[Vrooming Intensifies]

A kid's pocketbike complete with things like brake (singular), belt drive, chassis mounts for electronics, and bodywork ripe for plastering with obnoxious stickers.

Stock, they come with a 250W brushed DC motor and controller, and some SLAs. However, this was soon going to change.


Womp @_____@

Courtesy of MITERS I was given one of these things. A copy of a Hacker motor, and mechanically very similar to Hobbyking's 150cc Rotomax offerings (same mount pattern and external dimensions), this little guy (dubbed the Tiramisu) is good for ~10kW with a nice and low kV (100RPM/V) for vehicular operation.

Running the show is a 72V 100A Kelly sourced from no less than Dane.

But Noel, the motor has the shaft on the wrong end!

Have no fear, italicized text: we thought of that already. We have the technology.

In search of the one true shaft, I began by removing the end-bell shaft. Unfortunately, these motors had gone swimming once upon a time, and the four fasteners keeping the shaft attached had suffered from the softening. 
Ripe for stripping

Initial attempts involved using the correctly sized hex heads, but that resulted in the inevitable stripping of the heads, so I resorted to gently hammering in a slightly larger torx bit.

Success!

In hindsight, I should've left the end-bell shaft on for initial disassembly, however, it led to the discovery of the bolt keeping the real shaft secured to the rotor.



After the liberal application of WD-40, the shaft bolt was removed and I undid the motor mount-side screws keeping the can attached. The rotor and stator assemblies then happily came apart after some pulling. Undocumented is the use of the mill to pull things apart: I clamped the motor mount in the vise and used the drill chuck attachment to grab hold of the reinstalled end-bell shaft.

Afterwards, I took the rotor assembly, removed the end-bell shaft and the bolt securing the one-true shaft and clamped the can in the vise and pulled yet again.


Pliers unrelated


Tape was applied to the magnets promptly after removal to prevent crap from accumulating in the air gap.

With the shaft extracted, I took some measurements and turned a new, longer one that would protrude out of the mount side. The taper was completely unnecessary and may as well just be a step to make machining easier.

Left: Original. Right: New and improved.
In reality, this process took a few tries to get right because I tried to jam things together with a hydraulic press after machining the initial shaft slightly too large and wound of destroying a bearing that had to be angle-ground off of it  I suck at turning things and was too lazy to do it right the first time.

The tolerances on the motor are such that the bearing interfaces with the shaft are slip fits, while the interface between can and shaft is a press fit.

Reassembled, things looked pretty good!


Whew

The motor mounting bracket was also made out of a piece of U-Channel left over from last season's car.

U-Channel evolved into ... angle bracket ಠ_ಠ
In the back of my mind this whole time was also the fact that I had to mount a pulley to this thing, so afterwards, I went ahead and also filed down some flats on the shaft for the pulley that would mount on the shaft. Thankfully, the bike came with a standard 5M HTD belt, so I could buy a pulley off of ebay.

Almost a thing
Also sent out was a hall sensor board to play with the Kelly. The motor is a 10 pole pair affair and using some math, I established the mechanical spacing between sensors. That is:

1 rotation = 360 mechanical degrees = (360 * N pole pairs) electrical degrees.

For this motor, we get 10 times the number of electrical cycles per mechanical cycle.

Going further, we get a conversion factor of

0.1 mechanical degrees = 1 electrical degree

So for 120 degrees of electrical offset, we need the sensors to be mechanically offset by 12 degrees.

The idea of having the hall effect sensors mounted to a board was also attractive, so I went ahead and made a board in Circuitmaker in part to get some more experience in the Altium-like environment, but also because importing funny board shapes was especially convenient.





The design is a blatant knock-off of the boards Charles has made in the past with adjustments made to fit the larger can size and pole count of the Tiramisu and the addition of a JST-XH connector on the back. You can buy Charles' stuff here.

As a Circuitmaker project, all of the files are free to access in their community vault. Just search for "Tiramisu Hall Board" in the public projects bar.

IRL



With board made, I made up a quick mount in Solidworks that I ended up printing and bolting to some holes I drilled in the motor mount.


Rawr
Note: I'll probably redo the design and add some support material between the standoffs to prevent bending and the terribleness that is encoder misalignment.
Motor on a Bench
Unfortunately no video was taken during the encoder tuning process, but it went a little something like this:

Whirrrrrrrrr

>Looks at current draw
>Adjusts Encoder

Whirrrrrrrrr

...

Once the position was settled, I filed down some flats on the motor shaft, mounted the pulley and everything was dumped into the frame.




Next up: batteries and wiring!

Monday, May 15, 2017

INTRODUCING TEE-MOBILE

Following this year's FSAE season, I had the burning desire to make something "fun" again. No more messing with the Sevcon until dawn, or trying to convince other people to show up and do some work, or getting bogged down by schoolwork (not that it really stopped me from working on car).

Of course, this resulted in taking things way too seriously. As a result of planning out the car team class' curriculum for next fall, all I could think of was the meat of the design process. Designing to spec, meeting a performance goal, taking into account your budget, getting to make something cool to get around a problem.

And so, I met myself somewhere in the middle - an electric go-kart. In partial fulfillment of my desire to whip around the new engineering building at Tufts in style, and to have a working electric vehicle again, I started on the aptly named Tee-Mobile about three days ago.


Partially Transparent-Mobile

I started with a performance goal and a budget- hitting 20 mph in around 10 seconds, but also spending less than $600. So, I whipped out a spreadsheet and used some good ol' idealized physical models to get me some enumerations.

Spreadsheet

From my mechE friends, I've been told that when you start designing a vehicle, you start with the tires, then go to the suspension and chassis, and then the powerplant you need to hit the numbers you want.

I of course, was granted the luxury that there was almost no chance that I'd be doing burnouts with the current state of cheap scooter-worthy parts, so contact points weren't an issue. (I'd need something upwards of 22kW to get a burnout going from standstill)

I had no intention of having a suspension given the terrain would be entirely smooth, and I didn't have that many restrictions on the chassis - a fairly small turn radius would be nice, however the primary concern was whether I could fit on it or not.

So, I got to skip a lot of the hard stuff and went to pick out components.

Quickly, I discovered that this would be kind of hard to pull off.

The game was essentially "find the low end torque" - not especially hard with electric motors, but kind of hard with hobby airplane parts.

Starting with the motor:

I settled on the Turnigy SK3 6374.

Has a kV of 192 RPM/V, and is rated for 2.75 HkW (Hobbyking kilowatts). Alternatives included some offerings from Alien power systems, and other wholesale RC sites, but the 6374 wasn't so fast that I couldn't gear it down sufficiently, nor was so large that it couldn't fit in my preferred u-channel vehicle construction method.

I also wouldn't feel too bad putting ~4kW through it for short stints. Cooling will definitely be negotiated, with an auxiliary 12V supply on board to power fans, but also fancy lights and the like.

Once that was settled, I could then move forward with futzing with the steering geometry. Run of the mill Ackerman was chosen because we're going to be spending most of our time at 'low speeds' and I'd like the wheels to last more than 5 turns.

Going in circles: no longer a bad thing

Other niceties include an actual chain tensioner that has a spring. Having learned my lesson from the scooter, I have also opted to include all four mounting posts for the motor.

Impeccable
You may have also noticed the lack of brakes: having gotten sick of doing mechE things, and not enough of the zappy things (although in the spirit of the sloth, I may even avoid that), I opted to go for the latest and greatest in cheap Chinese motor controller technology, which implements not only regenerative braking, but also SINE DRIVE. Let's just hope I'm not rolling down a hill when the batteries are already dead. 


Big controller or small cart?
For now, the 1.5kW, 18 FET version of the latest Chinese brushless motor controller was chosen, but we may downsize and hope that whatever FETs in the smaller, 12 FET variety are equally capable of being overdriven via forcible resizing of the current shunt.

To be continued!







Monday, January 9, 2017

AND NOW BACK TO OUR REGULARLY SCHEDULED PROGRAMMING

MOTORS

An autopsy of the YASA was performed in lieu of its failure at competition. On site, the controller was throwing encoder faults, the reason for which became incredibly apparent once we'd disassembled the drivetrain.

Motor Exposed to the Elements

Tears T____T

Due to some negligence on behalf of the mechEs, the motor regularly sat in the shop without its dust covers on, which resulted in a foreign object entering the gap between the optical encoder and the encoder grating. One of the optical encoder housings was then bent and upon bench testing, was shown to be broken.

Top Side

Extracting the encoder board from the motor revealed a fairly run of the mill quad diff amp package that amplifies the photodiode current from the encoders to give the usable UVW output used by the motor controller. The encoders themselves are shimmed with a 3D printed member that gives the appropriate curvature when seated around the motor's circumference.

Bottom Side

The JST style connectors are for thermistor breakouts that are fed through the main "DATA" connector. Further, the board appears to have a conformal coating, presumably for HV isolation (the encoder board sits in proximity to the phase leads of the motor), however, gently probing the soldered through-hole leads showed that it didn't really do much in terms of insulation (lol).,

The replacement component comes in the form of the Sharp GP1A58HRJ00F, which is their drop in replacement for the broken part (The old part has since fallen into obsolescence).

Testing of the repaired board will continue once the rest of the drivetrain is back in order.

BOARDS

Motherboard
The motherboard and steering wheel boards were respun. The motherboard features many of the same things from last year's car, just in a condensed form. Since we were moving all of the low voltage electronics into a smaller, weatherproof box, space savings was the biggest priority. Further, simplifications to the I/O were made, which meant we could use just a single AMPSEAL 35 pin connector. Note: the relays required for the FSAE hybrid latching circuit took up a considerable amount of space.

Following last year's cue sheet, the micro takes care of the start-up sequence, and also monitors system conditions (tire pressure, motor rpm, current draw, speed, etc) which it can relay to the steering wheel micro for display to the driver.

Refinements were also made to the steering wheel electronics (see mechanicals here).



The steering wheel board was separated out into three parts: a main board that has the microcontroller that drives the main display, shift registers, buffers, and level shifters, and two LED breakout boards for indicating state of charge for the high and low voltage supplies. Having the boards separate meant that we could independently mount each section to its respective location in the steering wheel assembly, making our lives a little easier.

Development for both platforms is also done on Arduino given the low complexity and performance of the required systems.

Infotainment System

The display chosen was a 128x64 pixel Adafruit OLED module; using their included GFX library, the dashboard layout was done in a single evening.

LIDAR SCANNERS AND STUFF

In an effort to enhance the engineering curriculum at Tufts, a suitemate and I got involved in making some lab material for ES2, a general coding class for engineering students.

We were tasked with making a 1D and 2D scanning system that used one of the dinky ultrasonics sensors you see floating around everywhere.
http://arduino-info.wikispaces.com/file/view/sku_133696_1.jpg/495546144/632x632/sku_133696_1.jpg

To keep costs low, we decided to go with a nested approach; that is, the 1D scanner would be a subset of the 2D scanner. Pictured below is the 2D scanner - the 1D version would simply exclude the L-shaped "arm" and secondary motor, and then mount the sensor directly to the main motor stage, giving control of only yaw.

2D Lidar Scanner: Now with 50% more floating Arduino
The base plate consists of a lasercut piece of acrylic upon which the main stepper motor, arduino, and legs are mounted. The "arm" member is attached to the main motor using a set screw and shaft that's integrated into the arm's body.

Since the arm would be 3D printed, a tradeoff was made between print-time and strength: it features an I-beam structure that decreased print time and weight, and also allowed for convenient cable routing. 

The secondary stepper controlling the pitch angle, is mounted on the arm and holds the sensor using another 3D printed member.

Cable routing is done to reduce the cable strain without resorting to drilling out motor shafts.
Beginning from the sensor side, a small cavity is included past the expanded through hole for the motor shaft that feeds into a port in the arm - this will also double as the feedthrough for the motor leads. Shielded cable would be used to minimize interference between the sensor data lines and the motor lead wires.
Cable Routing
The cables then travel along the inner wall of the arm and pop out the bottom through a port located next to the main motor. 


 Also visible are the endstops - just some brass rod that's press fit to prevent either axis from over-rotating and pulling out a cable.

Electronics to be done soon...

Tuesday, December 29, 2015

WELCOME TO CAR TEAM, HOME OF THE CAR TEAM

Semester is finally over! Of course, this only means that the time previously dedicated to schoolwork is now consumed by cycling and CAR.

This week I've been getting the boards in line to be sent out to Advanced Circuits. Namely, the GLV motherboard, as well as the board for the steering wheel and HV panel.

A board for the steering wheel?
Yes!

In addition to integrating the low voltage electronics onto a board in a reasonably sized box, the dashboard is moving onto the steering wheel. This meant I had to yet again moonlight as a MechE.


A thing of dreams @____@

The design change was motivated by the poor ergonomics of the current dashboard mounted user interface, as well as the sweet steering column connector that was discovered while overhauling the cockpit. The original plan was to have an ARM based microcontroller running the whole show, but given the limited number of pins on the connecter, I opted to run the display on an AVR, and have the motherboard talk to the dash over I2C.


Asploded

In the center is an OLED display with an array of LEDs to indicated the SOC of the main and GLV batteries. In an effort to improve serviceability, the steering wheel is constructed in 6 parts: the backshell, the front grip, rear grip, LED diffuser (the acrylic bordering the screen), the face, and the quick-release adapter. The backshell can be removed for easy access to the boards inside (boards are mounted to the face).
The face and the quick release interface will all be made of aluminum, while the grips will be 3D printed, primed and coated with a rubberized finish, and the diffuser will be laser cut acrylic. The assembly is held together by socket head M4 screws.


Asploded


Buttons mounted to the face of the steering wheel will ether be hardwired to the steering column connector or to the nano breakout depending on its function. Functions on the previous dash like the brake bias adjust, and cockpit emergency shut-off switch will be kept in a separate dashboard area  in order to minimize clutter on the wheel face. (read: fitting an e-stop button and a knob with a cable running off the other end is a nightmare waiting to happen).







Saturday, August 29, 2015

BATTERY PUCKS, BUCK CONVERTERS



Butteries
With but a few weeks left in summer, I decided that it was a good idea to start designing a sort of universal battery pack for silly EVs.

The goals of the project are to incorporate the following features:
  • Integrated BMS 
  • Output protection 
  • "Hot-swappability"/fancy latching holder mechanism 
The integrated BMS would likely come from one of those newfangled Chinese BMS boards flooding eBay, and a fuse integrated into the output port would prove a nice alternative to a hot, smoky death.

To elaborate on hot-swappability: the concept of having an easily removable battery unit in an EV has always been an attractive feature that is almost always countered with "I'll do it later." More seriously, doing it well involves adding some mechanical latching mechanism to hold the batteries into the vehicle along with a backplane of sorts to mate with the battery. Further, packaging becomes more important as I can no longer just shove some wires to the side and call it a day.

The idea is that I'd have at least two of these modules in parallel in any given application, allowing the system to stay on as one pack is replaced after the other (how necessary this is in a derpy vehicle is another question), as well as allowing for the increase in capacity so long as there are empty backplane connectors.

Taking a cue from modern cylindrical cell based EV packs, I started with a modular frame structure.
Buttery holders
Slots were included above and below for balance leads and space was included for the battery tabs. Holes for M2 fasteners are also there for insulation mounting.

A few test prints later, this appeared:

It fits!
IN OTHER NEWS:

Buck, buck, buck, boost
I finally got around to tuning and laying out the hysteresis controller for the buck converter.

Features:

  • FOD8314 gate driver w/optocoupling and desaturation detection
  • Totem pole output capable of providing 30A of gate drive. 

One of the reservations I have about this board is the implementation of the gate drive power.

After looking to the ends of the earth for fancy DC-DC bricks, and inverting regulators beefy enough, I finally decided to cut my losses and go with a pair of isolated bricks since, well, it's easy. Further, it would cost me all of $0 instead of whatever Vicor or Murata want to charge.

TO BE CONTINUED

Thursday, July 30, 2015

FAST CARS, FAST CIRCUITS, FAST POTATOS

A semester and half of the summer flew right by! A few updates:

Tufts Hybrid Racing won the electric category!
Net sleep defecit ~50 hours

As electrical lead, I couldn't be happier. Moreover, the experience of going to comp and tech was invaluable.

A few lessons:
  1. Strain relief is a thing.

    To put it frankly, most of the car's wiring is atrocious. Done with crimp terminals and wire that was often too small, things had a habit of jiggling out of place. The result would be things like relays not turning on, and safety circuits triggering prematurely.
  2. While doing hardcore stuff is awesome, it doesn't get you past tech.

    I think this is more than evident in this year's very low tech pass rates. I saw cars at comp with custom BMS solutions, hub motors (drools at IIT), integrated dash displays, CAN networks, and a whole host of innovations that I would die to have the time to implement. In the end, we didn't go that route. I'm glad that at a point very early on in the fall semester, I decided to pass on stroking my ego. Case in point: I originally planned on implementing the accumulator indicators with some fancy DC-DC bricks, however, they decided to die at comp. Not wanting to waste any more time,  an LED + resistor solution was whipped up.
  3. Documentation will save us (all)

    One thing I was very glad about was the fact that Alyssa and I had spent so much time beforehand churning out documentation by the pageload. If anything, having proper schematics and system diagrams made the inspectors more likely to cooperate and made the inspection process much simpler. Further, LOOKING AT THE TECH INSPECTION CHECKLIST BEFOREHAND will prepare you more than anything.
     
  4. Batteries are a pain in the ass.

    The saga began with the addition of the pouch cell rules for 2014. The rules required a host of safety feature required of li-ion pouch cell based accumulators. Namely:
      1. compression limiters
      2. padding between cells
      3. a repeating frame design 
      4. complete modularity of the cells.
          And so, about a week into the spring semester, bricks were shat and the hunt for cylindrical                 cells began. We ended up settling on the 40152 15Ah headway cells as they allowed a few                   things: 
      1. No pouch cell rules
      2. Similar pack configuration and capacity (80S1P vs. 71S1P of the previous pack)
      3. "Implementable" packaging.
          I say implementable in that we were limited by our fabrication capabilities. In the end, we had to reuse our old sidepods and jam in all of the old electronics with some new electronics and bigger cells, which resulted in a very contrived game of Tetris. I think there was about 5mm of clearance between the cell stacks and the sides of the box after putting in the FR4. Further, had it not been for the grace of UVM, the acres of Kapton tape required to insulated everything from each other inside the pack would not have existed. <3 UVM AERO <3.  

With that said, we will probably have to redo the batteries yet again for Lincoln next year lol.

Other Observations:

Car was extremely slow. The controller was throwing errors at us left and right as we put the hammer down; in my sleep deprived state, I wasn't sure if it was because of a fried/improperly installed HVD causing excessive contact resistance or the Sevcon was throwing a fit because of some ongoing throttle parameter issues. Regardless, further debugging once we move into our new shop space will definitely happen.
In other news:

I've been working with a Tufts Lab over the summer doing some work for Zildjian. In the process, there's been a necessity to interface some good ol' analog with an fpga.

Of course, this meant laying out and implementing a front-end.

Squiggles of Science
The board is meant to interface with the Atlys Spartan6 based dev board from Xilinx. The slightly totally unnecessary meanders were trace matched to 5 mil and layer thicknesses were calculated to achieve proper 50-ohm characteristic impedances for the topside traces (not that it mattered either lol) with a ground plane extended to the 2nd layer (yellow) for the topside digital traces. I ended up using a THS1007 as the A to D, which has a pin compatible sister, the THS1209, which can do up to 8MSPS if need be.

It wasn't known until much later into the project that the desired frequency regime was actually much lower than what I had designed for. I guess this is what I get for doing what the PI asked.


Erp-amps


The analog side was pretty simple - just a few buffer amps, gains stages, an AA filter, and the level shifter required to interface with the A to D. J-fet amps were chosen for their high input impedance and excellent high frequency performance.


IRL
Stylish red wire was used to air-wire the +5V line to the buffer amps since a short developed between the trace and ground. After reviewing the Gerbers, I'm still pretty puzzled how something like this could've happened. MyroPCB, pls!?

Given that the trace was buried under the top layer, the impromptu solution was to beast it with a power supply until the trace burned out and cut a few traces. Burn, baby, burn.

Fast potatos to be discussed later...



Wednesday, December 17, 2014

SLEEPLESS (IN SEATTLE) LAYOUT AND DESIGN REVELATIONS

With finals over, but a few days still left in semester, I took the opportunity to finish laying out what was aptly named the Nevcon Gen1.


I tried to condense the board into as small a space as possible, which meant I couldn't fit the optos and related necessities onto the board - at the very least I shaved ~$10 off the BOM, And with the relative abundance and swapability of arduino nanos, it's a feature that may be toyed with if a micro is ever soldered straight onto the board. Did I mention that the board is 3"x 2.8"? :3

Further, in cheaping out in the switching converter department, a rather unfortunate consequence was the requirement of a huge inductor. Not a huge deal considering passives come pretty cheap, but is pretty ridiculous when its footprint approaches that of your FETs.  



Speaking of FETs, they were moved to the bottom of the board for increased heatsink mounting capabilities. The arrangement appears promising, but seeing how cooling such a power dense object might be a problem, I'm quite inclined to ditch the fancy surface mount switches for some good-ol' TO-220s. 

To be continued...

Tuesday, December 2, 2014

Motor Controllerino, pls

After spending the better part of Thanksgiving break suffering from severe phase lead (diurnal living is overrated too hard), I thought it'd be wise to use the time on yet another project: a BLDC motor controller. Given that I wouldn't have the funds to complete the godly hysterically controlled buck converter until at least the end of summer, something on the smaller side could provide the amusement one needs when suffering from end of semester burn-out.

And so, the list of requirements was born.
  • 2kW continuous operation
    • This means at least 60A given a 10S pack. 
  • derpy voltage and less-derpy current control schemeability
    • From looking at homebrew controllers, open loop voltage control with block commutation seems to be the most common, but at some point current control would be nice (something, something, torque). Note that I'm avoiding fancier control schemes (sine drive, FOC), mainly because the algorithms involved typical take up more time on your cheap hobbyist microcontroller, thus limiting the commutation frequency.   
  • sensored commutation
    • Allows for starts from a stand still (extra important in vehicles such as pocket bikes and go-karts). 
  • low-cost
  • serviceability
    • I say this mainly because after having made so many boards with parts on top of parts and impossibly close clearances, it might be time to make my life a little easier when debugging. Maybe. 
Being ever so inclined to start by making a board, I went on the hunt for components. I ended up settling on many of the same components that the later iterations of melontroller used: D2PAK FETs, the same current sensor, and the same arduino; I was attracted to the power density of the D2PAK package (how heatsinkable they are is another question) and the modularity of the arduino nano, however the only current sensor I'm using will be on the DC-link. This is to avoid cost and to employ phase current estimation via techniques discussed here and here as opposed to having a hall effect sensor on each phase.

As for the drive electronics, I settled on these bootstrap ICs (LM5104) after being a little sick of discrete gate drive, which inevitably leads to a board space nightmare. Floating drive rails were out of the question considering I'd be driving FETs with under 4000pF of gate capacitance. Everything seems so cute after having to drive bricks.

Other considerations would be opto-isolating the gate drive from the arduiner - a habit I intend to continue after having seen too many micros and 74 series chips die to failures in the power side propagating to innocent logic. Note, optos with built in logic output may seem convenient, but often have propagation delays up into the tens of microseconds - not good when those microseconds constitute a nontrivial quantity of clock cycles and degrees of rotation. I'll probably end up using some variant of this (6N137).


Time for some board layout...


Saturday, July 5, 2014

A Midsummer Night's Blog Post

WHERE DID ALL THE TIME GO!?

No matter. 

IGBTs! IGBTs! IGBTs!

LOOK AT THESE IGBTs!



Current limited by the package leads, among other things, these are the perfect candidate for some pulsed, hard-switched, power dense goodness.

And so the journey to building a QCW bus modulator begins.

In essence, the modulator portion of your QCW coil is just a buck converter capable of producing arbitrary waveforms across the bus of your DRSSTC.

The tried and true control scheme for these guys is hysteresis (bang-bang) control, which involves turning on the high side of your buck converter when the sense voltage falls below your hysteresis band and turning the high side on when your sense falls below the hysteresis band.

In lieu of a microcontroller, I opted to make my control loop out of op-amps for noise immunity and beardy-weirdy cred.


Troller Schematic. Forgive me, for I have text overlap up the wazoo. 
The first two op amps are set up as an adder and differentiator, which produce the hysteresis band given the input waveform. These signals are then passed to the latter two, which acts as a window comparator.

The outputs of the comparators are then fed to an SR latch so that the hysteresis thing happens.


Squiggles of Science
The control loop can then be tuned using the width of your hysteresis band or some fancier processing downstream.

Eagle'd:



Special notes: the input signal is actually taken from an opto, which is filtered by an LC to reproduce the desired waveform. It's like L-C filterception. Additionally, this allows me to send square wave pulses optically, instead of an analog signal through a long length of coax, which is bound to cause massive damage pick up noise.

Here it is in board form:


Note: not fully routed not the actual board
After doing some math and running the simulation for the bus at full load in spice, I concluded that I simply couldn't find bus caps large enough and in the desired package, so, the some revisions were made to the design.

The boards are now split up into three sections: a DC-chopper motherboard, controller daughterboard, and DRSSTC with filter LC.


Can't have too much bus cap (a work in progress)
By moving the filter LC to the DRSSTC bridge, I could then populate the DC-Chopper with as much bus cap as my heart desired (and keep the ripple voltage below 5%).

The addition of the driver daughterboard would allow me to send out for plenty of driver revisions without having to spend a fortune on the whole 5.5" x 5.5" board. Oh, and did I mention how small everything is? :3

Current limiting is implemented on the driver side as desaturation detection: in an over-current state, the voltage drop across the switches increases to well above the typical ~2.0V, which is detected by the drivers, which do some fancy soft-turn off to prevent voltage spikes induced by the typically high dI/dt. The gate drivers also conveniently have built-in opto-isolated inputs.

IN OTHER NEWS:

Bluescooter got an overhaul to make it more of a reliable commuter vehicle than junkyard scrapper on the verge of collapse.

After eating through a current modded controller, a few things were changed:

1) Motor upgrade!


Sweet Bajeesus
After trolling around the internet for a sufficiently large motor, I had at some point chosen this guy:

http://www.hobbyking.com/hobbyking/store/__18179__Turnigy_Aerodrive_SK3_6354_215kv_Brushless_Outrunner_Motor.html

An especially squat, low kv motor, perfect for squeezing into the tiny 4" u-channel frame. 


But everything changed when the fire nation attacked the motor went on backorder.

I was forced to look beyond Ye' Old Hobbyking, and found a cheaper, dare I say, better option:

http://www.sdshobby.com/emp-n-series-outrunner-brushless-motor-n6354200kv-p-2486.html

Even with expedited shipping, the SDSHobby motor lends itself to be a good $20 cheaper than the Hobbyking equivalent, the only downside from ordering from SDSHobby being their rather small selection of EV-sized motors.

2) The controller with the infinite heatsink


After eating through a controller, and being too lazy to replace the dead FETs, I opted to avoid yet another headache by heatsinking the controller to the chassis.




Some fresh thermal grease, three holes, and some cap screws later, a happier 'troller was born.
Even on especially hot days, I've yet to find the area around the FETs go more than 5°C above ambient. 


3) It has a new caddy. 



Structural Hot Glue


Made entirely out of mystery plastic polypropylene and a bit of polycarb from MITERS. The key switch was also moved to the outer face of the port panel to accommodate for the larger motor. 


Fin.