Wednesday, October 8, 2014

Cholo @ MIT Maker Faire!

Some pics of the EV-Allstars at MIT! Taken by Josh Ramos during MIT's first Maker Faire!

Tuesday, October 7, 2014

Cholocycle: upgrade components finally here!

After a long wait.... over the last couple of weeks I have received some awesome new presents:

Sevcon Size 6! WOOHOOO
OMG SO MANY A123s! (i'm using two 13s3p modules!)
Delta-Q Quiq 1kW charger!
Let the preparations commence!
 I will be using 13s3p modules now (as opposed to 13s2p), this gives me 50% more energy and range than before! Here is an updated plot of my range estimates!

70 mile city and 50 highway! not too shabby!

Me and a group of awesome helpers have started planning the system upgrades. We have dismantled the old system (held together by wood and zipties) and we are sizing the components and mounting strategy.

not the final configuration!

I also have bought a new sound system for the bike (Thanks BOSE!)

With these new components and my awesome new crew of volunteers I am hoping to be working on this project more and be done (street legal) by the end of January!

Wednesday, July 30, 2014

Cholocycle Perfomance Estimates


Batteries are still not here, so I have been doing some math instead.

I set-up some matlab code to give me performance specs of the bike. I started off with the torque curves from

I am using 85V 650A so I selected the 72V 650A curve as the closest available. This is the peak curve which is useful to estimate the peak performance of the bike (not to be confused with the continuous curve).

From this torque curve (in orange) i made my own "simplified" torque speed curve.

Having the torque characteristics of the motor now I input my specs for the bike (gear ratio, wheel diameter) and I scaled the Torq-RPM graph to a force-mph graph. I also assumed some drag coefficents and some rolling cofficents and plotted a Resistance-mph graph. I then compared them as below.

With this graph I can estimate the steady-state speed of the bike, this is when both curves intersect. This shows about 96 mph top speed! Not bad!

I can also compare the power curves:

Notice that the inserct in the power curve occurs at the same speed as in the torque curves, which suggests consistency in the model. From the power curves I can see what my consumption should be at every speed by looking at the drag power. Black dotted line shows 8kW which is the max rated continuous power of the motor, this says I should be able to cruise around 60mph continuously without overheating (till my batteries run out).

Now that I know my power requirements at every speed I can figure out how much range I have at every speed. This is simply done by dividing the kWh of the pack (5.3kWh) by ( 1.1 * power required to stay at that speed) The factor of 1.1 is there because I'm assuming 90% efficiency of drive train (motor, chain, tire).

This is that graph:

So it looks like 50+ miles for city driving and just under 40 for highways. sounds about right to me!

Lastly I wanted to get a sense of the dynamic model of the bike (everything up to this point is steady state, i.e. no acceleration).

In order to do this I made up a quick simulink model that includes the peak torque speed curve from before and also includes the air drag, rolling resistance and mass of the bike. Here is the simulink model.

With the model now I can estimate my acceleration.

So it looks like 0-60mph in 4 seconds. I'm satisfied!

So here is a summary of the findings:
96mph top speed
0-60mph in 4 seconds
50+ mile in city and <40 highway.="" in="" p="">

This is assuming the following:
AC-20 Motor
Sevcon Gen 4 Size 6, 650Amp Limit
85V nominal pack voltage (A123 prismatic 26s3p)

For those other e-moto riders out there, does this sound reasonable? Please post your replies to in this thread:

I'm eager to get my batteries and controller and test cholo out!

Wednesday, July 9, 2014

Cholo and Harley-D's Project Livewire

As you probably heard Harley just released a prototype electric bike. They are currently touring the US in search for feedback from customers before they make a production bike. They are calling it "project livewire"

I was lucky to be invited to ride the new bike at Boston Harley dealership in Everett on June 27th. It was a lot of fun. They also allowed a bunch of my friends with licenses to ride the bikes on the street.

I really enjoyed the bike! Instant Torque, nice sound, and great looks (arguably better than most electric bikes already out there, i'm looking at you Brammo and Zero!). I got it to 60+mph and i could have definitely gone faster without traffic.

I also brought Cholocycle with me (I had told the dealership I was gonna bring it), after about 10 min of Cholo being dispalyed I was asked to remove it from the exhibition! Apparently, corporate harley in wisconsin saw the bike in the "live feed" from the event and got scared at the amount of attention it was getting and asked for all "competition bikes" to be removed. It was kinda sad not to get to exhibit cholo for longer than 10 min, but I found it kinda flattering that THE Harley-Davidson considered my bike "competition".

Here go some pics for the event, mostly taken by Charles.

Friday, July 4, 2014

Chologoodies: Charger, Decals and Tach Sticker

Still waiting for batteries and gen4 controller, so i have been distracted by adding some peripheral goodies to the bike. I'll let the pictures talk by themselves.

arduino nano wired in to interface with the tachometer (now a current meter)

joey putting the charging platform on the bike

retractable cord assembly from an old vaccum cleaner

charging up the bike with the small on board chargers

retractable cord coming out of gas tank! not super practical but it is a neat piece of poetry and gives a new meaning to fueling up your bike

HV, MIT and Beantown Taqueria stickers!

representing the coolest center at MIT (

new tach/ampmeter sticker!

Friday, June 13, 2014

getting the Cholo ready for the road p.1

Still waiting for my batteries and Sevcon Size 6... so not much has changed regarding the power train of the vehicle. I have decided to spend time and money getting ready to get the bike road legal. I bought a bunch of stuff including: new brake pads, new rotors, new brake fluid, a new gauge cluster, rear view mirrors etc.

I am still looking for a ZX6E front fairing (can't find a decent one on ebay/the interwebs). I also made and added a spacer to the motorshaft and a shaft collar so now the sprocket is axially constrained on both sides and I dont have to depend on the set-screw/locktite for any constraint on the sprocket. I also got to use some sweeeeet new lathes (Proto trak) and after using them it will be extremely hard to go back to any other lathe.

brand new brake pads and brake fluid!

hacking into the tach

using a function generator to hack the tach into showing me current

the tach responds... now to hook it up to an arduino to show it in real time

The tach normally runs of the signal from one of the ignition coils, you can fake a coil signal by any periodic signal (sine, square) etc of around 5V-12V, i used a function generator and then an arduino. Turns out every 20Hz is aprox 1.2kRPM for this bike (it'll depend on how many cylinders your bike has, mine had 4). It turns out if you use 12V you get the full range of the tach. With help from my friend Jacob we hooked up a hall current sensor that Charles gave me to an arduino. The arduino brings in the voltage from the sensor and then sends a pulse of a frequency that corresponds to the current into the tach. I offset the 0 current position on the tach to be about of a third of the way into the tach so I could also show negative currents and thus show much current I'm regening. Next step is to print a new sticker for the tach that says "current" instead of RPM! I am also planning to hack into the fuel gauge to show battery charge or voltage and also hack into the temp gauge.

I decided it was time to get into 3d printing so i decided to start printing some lug covers for the high current terminals on the controller and motor. After a couple of iterations I got a pretty satisfactory lug cover.

v2 and 3 of the lug covers, more coming soon!
I also replaced the speedometer cable and tested the bike in the hallway, I got up to 20mph! I don't want to go any faster than that indoors! I am still waiting for the bracket to mount it to the frame as well as headlights and other parts.

Next steps is to start wiring all the brake lights and turn signals. I might add a 12V battery and DC/DC to the system so that I dont have so drain all the power for auxiliaries from the sevcon. I am also trying to use as much of the old harness as possible (junction box, switches, connectors).

Tuesday, May 27, 2014

I'm Riding Cholo!

Hey folks, its been long since the last update. This was a busy semester (but my last, yay!). I spent the last couple of weeks debugging the sevcon controllers to work with my AC-20.

I rigged up my testbed in the EVT room.

EVT test room

making sure to keep tires off the ground

Sevcon espAC with the bike

in the process of testing cholo ride, I had to revive two dead cells in this pack

putting the controller into the bike!

bike with zip tied batteries (better batteries and battery mounting coming soon!)
blown fuse!!!! during some auto-tune testing

power supply+espAC for autotuning

After struggling with the sevcon for a couple of hours Dgonz and I finally got this to happen!

Finally we waited for sunny sunday to do this:

I rode it around campus for a bit (i didn't want to ride too much given the bike is totally not street legal right now). Lots of fun! I Still need to mess around with the settings and fine tuning of the motor to get 100% of the motor potential. Currently I have a 72V 15Ah LiFePO4 pack (1kWh), I am hoping to upgrade this to 5kWh soon. I am also waiting for a sevcon gen4 size 6 to arrive to finish the bike.

[a more comprehensive update for the sevcon troubleshooting will be coming soon! in the meantime follow this as it is the best online tutorial that I found, credit to dgonz for all the sevcon help]