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!