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Design for a Cause - The Ultimate Smart Trike Design Blog 2 of 4

Sean_Miller

 

Previous Blog:  Design for a Cause - The Ultimate Smart Trike Design Blog 1 of 4

 

BILL OF MATERIALS (FOR THIS PART OF THE BUILD)

In this episode, we convert the mechanical aspects of the trike to electric.  We are not tackling the "Smart" electronics at this stage.  We first need to understand the challenges ahead once we test ride it still dumb and dangerous.

 

The motor controller and throttle weren't worth a build as they are very inexpensive to purchase.  Since our build spanned multiple disciplines, not everything we needed was on Newark, so I included the raw specs with this BOM:

 

650W, 36V, 450RPM Output Geared Motor

34 Tooth Sprocket

#40 Chain

15mm bore freewheel

36V Thumb Throttle and Motor Controller

(3)18Ah Batteries Product LinkProduct Link

Molex  36663-000136663-0001 Product LinkProduct Link

Molex 36664-0001 Product LinkProduct Link

Molex  50-84-102050-84-1020 Product LinkProduct Link

Molex  50-84-202050-84-2020 Product LinkProduct Link

(2) Inline Fuse Holders

(2) 25 A Fuses

3" x 3/16" Carbon Steal plate

1/4"x 20 Grade 8 bolting

Dual Piston Brake caliper and hydraulic actuator (as found on ATVs)

Zip ties

 

 

MOUNTING THE MOTOR

After assessing the Trike and mocking up its rear carriage in Autodesk Fusion 360, we elected to mount the motor to a 3/16" plate that was then bolted to the top bracing of the carriage.  It allowed for a direct shot for the new chain after cutting the trike basket.  It also would allow for installing the batteries low to keep the center of gravity of the trike low.

 

image

 

We found there was not enough clearance to install the new sprocket.  So, we elected to eliminate the original band brake at that center location and install a disk brake at the drive wheel.  We plan to make this actuate from the MKR1000 versus by cable.

 

We wired the 3 batteries in series to create a 36V power source.

Here is the overview of the system.  Note:  At this point we don't have the MKR1000 Brain Box Shown in the diagram - so it's still dumb and dangerous!

image

Basically, the MKR1000 brain box we will make puts  3.3V to a transistor that, in turn, pulls in a relay.  The relay switches from its normally closed state to the open state.  Wired to the relay is the independent motor controllers brake interlock.  This, in turn, allows the motor controller to drive the motor.  Basically, we will hack one brake interlock to get interlocks on pedaling, speed, tilting, proximity, and alarm.  But first, we need to test it mechanically.

 

TEST DRIVE

It assembled nicely and Connor took the motorized for a test drive in its l dumb and dangerous state.

 

The test drive identified the following hazards:

  • You could easily run over your legs with the back wheels if you accidently hit the throttle when stopped with your feet down.
  • In a panic, its hard not to remember to take your thumb off the throttle while braking.
  • The original brakes do not stop the trike quickly enough.
  • The trike has to take wide turns.  Tight turns that you would do on a bike will actually cause it to go up on one wheel in the back.  This is not a problem for the paved rail trails we ride, but would be bad for a crowded beach.

 

We are very happy with the batteries.  We have ridden nearly 3 hours on the out-of-the-box charge!

NEXT STEPS

Stay tuned for our next video where we code and breadboard the "Smarts" of the design using the MKR1000 and various sensors of the maker kit.

  • in reply to Sean_Miller

    Not sure what their theory is, but it's one reason you won't see a proper Segway (just the baby asian style versions) in Australia.

     

    One thing I do note here in Christchurch is that e-bikes seem to be just a battery powered vehicle, rather than an electrically assisted pushbike.

    It seems to be a loophole that means you can ride this powered device on the roads for free and no licence, yet every other road user needs to contribute in some manner.

     

    Cheers

    Mark

  • in reply to mcb1

    I wonder if their legislation for road riding would be different if there were more interlocks proposed than just pedaling.  As the author stated 200W won't even get you up a hill, so they are limiting the desire for an e-bike considerably. 

     

    See ya',

    Sean

  • The first principle of building assistive tech is "Do No Harm!"

    Good thought.

     

    Obviously you have the brain box to go, but what about detecting pedal movement first before it applies motor power.

    You'd only have to pedal one revolution which assures the system both feet are on the pedals.

    Blog 4 shows you've done exactly that ... good solution.

     

    Your 650w motor might be overkill, which also could be part of the other issues.

    Australia only allows 200w motors or 250w if they are pedal assisted.

    (There is a discussion here which raises some valid points http://dillengerelectricbikes.com.au/blog/electric-bikes-and-the-law.html )

     

    You may also be able to apply a throttle/speed reduction in the turns, or simply physically limit the turning ability.

     

     

    Dual Piston Brake caliper and hydraulic actuator (as found on ATVs)

    You'll also need to be careful about the type of brake system you add.

    Many of the hydraulic units actually drag the pads, which is not desirable for this application.

    You could look at some of the downhill mountain bike versions.

    The larger the diameter of the rotor, the greater the stopping force.

    (something people forget when adding larger wheels to a vehicle)

     

    I did see that you're cutting motor power when the brakes are on, pity regen braking isn't available, or maybe you can dump a rectifier and charging cct across the motor when brakes are only just on??

     

     

    Lower the Center of Gravity:   on our Raising Awesome Channel, we will weld in the battery brackets that will locate the batteries under the trike.  This will take the center of gravity as low as it can go and move it under the rider for added stability.

    I was wondering if there was room in front of the rear axle and slightly below the centreline to mount one battery each side.

    The further out you place these the more stable it will be. You're still stuck with a single battery but this could be at the same height at the rear.

     

    Mark

  • in reply to dixonselvan

    Thanks for the comment.  We found a workaround for the video issue and I embedded it into the blog.  It now shows it in its entirety.  You can now see what the Simpsons would be like if Homer and Bart were Makers.  image

     

    I like your thought on the bar.  However, now I know why the Honda Elites were styled like they were.  (if you are old enough to remember them)

     

    The motor has a ton of torque.  If one's foot is planted on the ground, forward motion of the trike would clobber you even with the bar.  The Honda Elites and scooters in Just Cause 2 have a design that prevents setting your foot down in the path of vehicle mass at all.

     

    You gave me a thought though - I could have a bumper with a limit switch there as you suggested that would kill the motor and trigger the brake until a reset.  If something crazy happened - at least it won't happen for long.

     

    My wife road it tonight in "dumb and dangerous" mode and she felt compelled to let a foot glide on the ground as she pulled into the garage.  I freaked out.  The first principle of building assistive tech is "Do No Harm!"

     

     

    The easy thing to do is eliminate pedals and stick a platform there, but I still want the trike to be about exercise.  So, I'll chase the bumper approach.

     

    For spreading the weight - I'll use the batteries as my weight source and do exactly what you suggest.

     

    Keep the ideas coming!!!

     

    -Sean

  • Congratulations and Connor on making it upto a test drive and good luck for your smarts.

     

    I watched half of the video here https://www.element14.com/community/videos/26430/l/ultimate-smart-trike-blog-2 as you had mentioned you have some technical difficulties uploading the rest half. That half was really nice to watch as you guys build the Trike.

     

    May I suggest you to add a bar horizontally, welded in the front guard of rear wheel from one to other for the below? This way it will block your legs from traveling into the wheels. But keep an eye that it will not affect the movement while we pedal.

    You could easily run over your legs with the back wheels if you accidently hit the throttle when stopped with your feet down.

    For the below try adding / spreading the weight in the back from the Center that way you will lower the Center of gravity of trike in tight turns.

    The trike has to take wide turns.  Tight turns that you would do on a bike will actually cause it to go up on one wheel in the back.  This is not a problem for the paved rail trails we ride, but would be bad for a crowded beach

    image