More Guavascooter: Speed and Distance Testing

Today I took a little adventure to visit my good buddy Chris down over at Bolt IO, a new shiny hardware startup incubator located conveniently close to campus (and chinatown!). Needless to say, I'll be visiting often.

This trip, for this time anyway, included the use of the T, so I had to park my scooter somewhere on campus. When I returned, I visited the ME graduation banquet and then returned home for a bit. Later, I left my housing again for a meeting with my PI over in building 35. Nowhere throughout the day did I charge guavascooter. This was a perfect additional data point to hopefully better estimate traversal distance. Here is the route:

A total of 3.5 miles. using the numbers from last post, we expect a battery expenditure of about 1170 mAh per mile. However, today's route only used 3170 mAh, which means approximately 905 mAh were expended per mile. This results in a projected distance of 7.6 miles. Lets say 7 miles just to be safe.

The second test that day was the speed test. I selected the section of road between Amherst Alley and Mass Ave as the trial space. This is a roughly half-mile section of road.

My timer showed I made the trip in approximately 1 minute and 52 seconds. This meant that my scooter maxed out at about 16 miles per hour. That's pretty slow for my tastes considering Razor Wind was estimated to run at 30 miles per hour and Razor Reloaded was to run at ~25. This is not a major issue but if I decide to address it I could change the sprocket ratios or select a new motor.

Cambridge and Guavascooter

I made it alive to MIT. Today marks one week of life up here. One week of life walking about because my latest scooter  just came today. Discussing the name with Charles, we decided a more fitting name for it was "Guavascooter", as an extension of Melonscooter except using the guava sized SK3 motors.

Without delay, here comes testing.

Tonight I drove this route to MITERS from my temp housing at Tang. Its about 1.68 miles as indicated by the picture above.

This route expended 1967mAh of battery capacity. From a 6900mAh pack, this means I could run this route about three times safely assuming voltage drop does not fall below 21V (ESC cutoff).

Tomorrow, I will determine the max speed of this scooter via time trials down Vassar street. More to post later.

An additional note, I am no longer using the chatparts.ltd esc in Guavascooter. The current ESC is a elifebike esc, which Charles and I will touch on later in the coming weeks. Cheers!

Gigarazor: The Practical Scooter (Backblogging)

About 5-6 weeks ago, I bought one of these from a fellow Georgia Tech Student.

What is it? That is a fully functional Razor E300 electric scooter. I bought it with the intention of making it even MORE functional.

I was looking at Cambridge and Boston now. A larger campus with more bumps of sorts from historical sidewalks and roads. I was planning some seriously legit mods to Razor Reloaded (another scooter you dont know about) but opted for the premade sturdy steel frame foreseeing a busy time ahead of me for the final few weeks of the semester.

So what was the plan?

• new motor
• new batteries
• proportional control
• big switch
• power consumption feedback
• new controller
• LEDs everywhere

I had bought a Turnigy Aerodrive SK3 6374-149 awhile back and decided it would be my motor choice.

After removing the old components, a motor mount was fashioned quickly from some 3/8" 7075 plate on the waterjet.

I had initially picked the Jasontroller as my brushless controller because my other graduating friend was selling his old equipment. Here is a unmodified no-load test from a bench top power supply.

The battery was comprised from generous donations from A123. This 8s3p pack shown below was bridged using copper mesh instead of copper braiding. I figured the equivalent copper cross section couldnt be any worse than the 12ga wire exiting the pack.

Completed and bundled. Yes, that is a DE9 female connector being used as a balance plug. It works wonderfully.

By this time I started riding it about campus. It did not have a main switch (on order from RMP) nor did it have a top plate. Regardless, it was hella fun.

Then came the top plate. Attempting to bend polycarbonate with a 40W heatgun...

...failing to bend polycarbonate with a heatgun.

Beyond Unboxing: Chinese E-bike Controller (chatparts.ltd)

This post is a preliminary to a much more comprehensive post detailing controller capability that will be made when I am nearby more legit diagnostic equipment. For now, this post will contain my conclusions from observation, use, and light modification.

The "Beyond Unboxing" series is inspired by Charles Guan's posts concerning these same type of escs.

The Thing:
I have purchased a marketed 24V, 250W brushless controller for e-bikes hopefully as a replacement for Jasontrollers. What caught my eye was the cheaper shipping, faster delivery time, and the seller whose English was grammatically correct. It arrived just yesterday and after some observations, I am very excited about this controller.

The seller even included pre-stripped connectors!

Its casing was a interesting trapezoidal feature. Still a single tube of extruded aluminum, still two silicon pads on either end captured by two stainless steel brackets. I even think they used the same screws...

The chatparts esc also has fewer wires. The seller includes a diagram of the connectors (without labeling the individual wires) but there are unfortunately more than 9 connectors on this controller.

In short, it is incomplete. However the function can be deciphers from the connector ends since these are meant to be direct drop-ins for existing EV systems.

The Comparison:
Now lets have a closer look at a jason and chatpart side by side.

Its smaller... Less thick by about 1/8"

Board looks less janky. The chatparts ESC (bottom) has only SMT components whereas the jason (top) does not. I was also intrigued by the 7 labeled vias at the top left of the esc (in this picture, in this orientation). Those look like programming pins. It may be possible to reverse engineer the software and find out REALLY how this guy works.

Again, fewer wires.

Ah the processor! Everything in here is ST Mirco stuff.

MOSFETs:   STP75NF75
Processor:     STM8S903K3

Performance:
My test rig is just my latest GigaRazor scooter (that none of you know about yet) with a watt meter inline with the power source. Note that this is a sensorless configuration. I will not be able to conclude as to what functions it has but I can at least detail its behaviors.

Unmodified Test runs:

• No-load behavior: Ramps up until near max throttle where controller experiences cutoff. Not choppy intermittent behavior, simply cuts-off. Repeatable behavior. However does not affect throttle behavior for subsequent runs. Lets consider this feature Controller Protection.
• Load behavior: ~20 Amps current limit stock. Does not experience high speed cutoff under load (perhaps I am not traveling quick enough to reach no-load speeds). ESC is cool to the touch.

The controller was then modified using the solder-blob shunt method.

Modified Test Runs:

• No-load behavior: Experiences intermittent cutoff at higher speeds. It is choppy, unlike the unmodified behavior before.
• Load behavior: increased acceleration as expected. Choppy behavior as described in no-load experienced in load behavior. Watt meter reads ~50 Amps peak. Case is hot.

The controller shunt was then lowered to 40A and then 35A afterwards. The choppy behavior still persisted. I took this opportunity to measure to case surface temperature and discovered it was in excess of 120 degrees F AFTER a run at higher current.

My scooter uses an 8s3p A123 LiFePO4 pack and a Turnigy Areodrive SK3 6374-149 motor. This means at nominal voltage I should be rotating ~3933 RPMs. However at charged voltage I would be ~4172 RPMs. For comparable controllers in this application, it exceeds the infamous RPM limit determined by Charles and Shane years ago. To validate the RPM limit cutoff, I will test no-load conditions again using a 24V nominal battery or PSU.

Conclusions:
I will withhold my final judgement until I can more easily explain its behaviors and features. For now I can summarize the main takeaways:

• Runs sensorless (sensored TBD although it has wires for it)
• Possibly has high eRPM controller protection
• Possibly has a second method of current limiting
• Possibly has over temperature cutoff control
• Smaller and cheaper than Jasontroller
• No self-learn

More to come.