Custom Build Gallery, Teklektiks dual-motor Yuba Mundo

November 14, 2013
5,839 Views

Alan is an electrical engineer and drives a Volvo station wagon (endless-sphere username: Teklektik), so it’s no surprise that when he wanted an electric bike for errands and a bit of exercise, he built a 2WD cargo bike. He has produced one of the most professional custom builds I have ever seen. In Alan’s build-thread, he wanted to share his expertise in the electrical field, so he provides schematics and every possible detail about what’s needed to create a comprehensive E-bike electrical system.

While reading this article, open a new tab and click on this link, and then click on “play” so you can listen to some music while you read…

 

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I wish I had a way to get to work like this New England bike path. The trees changing color in the fall would be beautiful.

 

General Notes

The choice of 2WD was made for redundancy to achieve a “limp home” mode and avoid getting stranded far from home with tons of groceries on board. Alan relates that he has smoked a controller 9-miles from home, and  simply switched off the offending controller, reset the breaker, and continued on his way!

Alan lives in a mixed rural/suburban (and fairly hilly) region of Connecticut where 15% grades are difficult to  avoid, and 10% grades are common (nothing is level). When running on a single motor, the bike will do 32-MPH  (CA-limited to 1650W), and with both motors it will do 40-MPH drawing 3300W. The dual gear motors make the bike torquey over a broad speed range, responding briskly to the throttle off the line, and providing a combined 150lbs of thrust.

 

New England in Autumn...

New England in Autumn…

 

Two thumb toggle switches on the left grip allow selection of one/two motors and lo/med/hi power levels to allow a variety of modes for different riding situations. Hills are usually tackled with both motors (while limited to a total of 2kW), while bike paths are run with a single motor that is limited  to 500W for stealth. General riding with speeds averaging 17-MPH provides a range of 40-miles from the 66V / 20-Ah LiFePO4 battery pack.

The bike ended up providing more types of riding opportunities than originally envisioned and preserving the front shifter and derailleur to retain all 21 gears turned out to have been a good choice. It serves as a grocery-getter running with traffic and also travels bike paths largely under pedal power. PAS from a Cycle  Analyst V3 gives additional riding options.

Overall the bike has a retro look with balloon tires, old-school headlight, reproduction vintage Lucas  motorcycle  turn signals, a round motor cycle mirror, and of course, the trademark Mundo luggage rack. The gear motors are inconspicuous and wiring is routed through the top tube giving the bike a clean appearance. Bike path encounters find most people unaware that the bike is powered.

 

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Yuba Mundo V4

Alan liked the Mundo and delayed the build a month to get one of the first V4.0 units (rather than the V3.3).  It weighs 4.5-lb less and has the space behind the seat-tube opened up for mounting components. To soften the  hardtail ride, the bike is equipped with 2.35-inch Schwalbe “Fat Frank” tires, a wide Sunlite “Cloud-9” cruiser saddle, and a Thudbuster-LT suspension seat-post…worth every penny.

For reasons of strength, Yuba upgraded their later Mundo models with a tubular fork to replace the earlier bladed fork. Although Alan’s bike has had no problems in 7500 miles, he has a new Mundo tubular fork in hand for a winter replacement project – just to keep ahead of any issues that might arise from prolonged FWD and disk brake stresses.

Motors

Geared hub-motors are appealing for 2WD because the internal freewheel allows the wheel to spin unpowered without drag (unlike direct drive motors) – a big plus not only for pedaling, but also for running on a single motor. A YouTube video of a dual gear-motor Big Dummy chewing up hills pretty much sealed the deal and Alan went the gear-motor route. He settled on dual BMC V2S motors from Ilia at http://www.ebikessf.com mounted to identical 26” Sun Mammoth rims.

 

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High volts in a torquey geared hub means Alan used two side-by-side torque-arms.

 

The stock BMC phase wiring is terminated shortly after exiting the axles with Anderson Power-Pole connectors so the wheels can be easily dismounted for service. 10-Ga marine wire is used from those connectors to the controllers. JST connectors are used for the hall signals.

[editor: We do not recommend direct-drive motors for the front forks on any build for a variety of reasons.  However, for the rear motor of a dual-motor build, a direct-drive motor is a good choice. We also want to point out  that a DD motor on the rear can provide the option of regen-braking, and also near-silent one-motor operation  when desired.]

Controls and Controllers

The bike uses a single Magura throttle to run both controllers via a Cycle Analyst V3 (CA) with power for both controllers routed through a single external Cycle Analyst shunt. Throttle power is drawn from the CA and the CA Throttle Out signal is run in parallel to both controllers. The identical motor/controller/wheel/tire  configuration makes the 2WD implementation straightforward since the two identical drive systems share the load and power equally in all situations – the single Cycle Analyst is unaware it is controlling two motors.

 

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This comprehensive electrical system qualifies to be an electric Moped that is legal to run in traffic, if you ever wanted to register a similar E-bike.

 

Two operator switches allow on-the-fly selection of either motor (or both) and provide three power levels – all implemented using the Cycle Analyst. With two motors selected the three maximum power levels are 3300/2000/1000 watts but with only a single motor selected the levels are automatically cut in half to 1650/1000/500 watts. The CA ‘Power Throttle’ configuration scales power over the full range of throttle motion for any motor/power combination. Operation is simple and CA does the heavy lifting behind the scenes.

 

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Even with 12-FETs each, these two programmable and adjustable Lyen controllers fit well under the Mundo’s welded cargo rack. Welded cargo racks never work their way loose or squeak.

 

The original 2011 build used two Crystalyte 72V / 35A / 12-FET analog controllers (not microprocessor-based) and a Cycle  Analyst V2, but in July of 2012 these were upgraded to Lyen’s 12-FET programmable EB312 controllers (modified for  geared-hub use) and a CA V3.  The V3 has Current/Power throttle and throttle-ramping, which are awesome features. The bike is now extremely smooth off the line and requires no special care to avoid wheel spin-out or to protect the motor gears or freewheels – seizing freewheels had been a problem until ramping arrived with the V3 upgrade.

 

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The recently added 16-magnet PAS, now Alans E-bike has a “no-throttle” option.

 

A recent addition has been a 16-magnet Pedal Assist Sensor (PAS), with an assist-adjustment knob located as a bar-end. “I confess to having been skeptical about the whole PAS thing, but I am completely won over by the change in riding experience. My favorite rides are on the “Rails to Trails” paths, that have miles of gentle grades. I just dial-in the amount of assist I want and enjoy a throttle-free ride through the woods. Turning the knob to zero will kill the PAS-assist and the bike returns to throttle-only operation.”

Batteries

“I went a safe route with the batteries for this first build and began with a 16S / 2P Headway design (53V /  20-Ah), but ordered enough cells and parts to experiment up to 16S / 3P (53V / 30-Ah). Over a period of months I tried different setups and finally settled on a compromise for weight and range using 20S / 2P (66V / 20-Ah) for a usable total of 1024-WH at 80% discharge. When I’m getting 25WH/mi, this gives a solid 40-mile range.”

 

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Headway are large for the amount of Ah they hold, but where they shine is the high current (C-rate) they provide.

 

The first battery was built as a pair of series-connected 8S /2P packs made of the 38120 Headway LiFePO4 cells from Manzanita Micro (38mm diameter, 120mm long). The packs were fabricated using stock Headway bus bars and 2-hole plastic spacers. Accidental shorts were minimized by using round insulating washers on the cell ends, cut from thick 40-mil rubber shower curtains.  This configuration evolved into the present dual 10S /2P configuration.

Pep-Boys plastic tool boxes were used as temporary battery boxes and served so well they were never upgraded. 1/4-inch plywood bottoms provide added stiffness and simple wooden blocks serve as spacers to prevent the cells from moving around. A high density foam block is compressed under the box lid to prevent the battery assembly from bouncing in the box due to road vibration and impacts.

 

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Headway also sells the configurable pack assembly components along with their screw-top cells.

 

On each of the two packs, a 50A MaxiFuse originally replaced a bus bar for pack protection, but after a while Alan noticed the fuseholders had overheated and melted to some degree. They were removed and replaced with bus bars. Newly arrived mini-ANL fuses and holders that use bolted instead of tension contacts will shortly take over the protection job. Meanwhile, the main circuit breaker has worked well, so there is no rush.

 

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One of two 16-cell battery packs, with a large 50A maxi-fuse and a cell-log.

 

The battery-boxes are supported on the Mundo side-loader bars with decks fabricated of wood-grained Pergo flooring  (MDF core with tough plastic covering on both sides). The exposed MDF edges are sealed with tinted epoxy to make them waterproof. Two inch polyester straps and industrial Velcro hold the boxes in place on the decks.

Charging

Partly because of the initial experiments with various battery configurations, the battery has no Battery Management System (BMS) and uses single cell chargers to ensure a balanced pack on every charge. With a forty mile range, one ride a day followed by a slow overnight charge has worked out well. The charger was fabricated of two 8-outlet power strips holding 16 single-cell Voltphreaks chargers in a  heavy-duty  ACHC5500 “Ape Case” from Amazon. Initial use showed the close side-by-side charger placement caused them to run hot, so a fan was added and every other charger was plugged into a thin pass-though Euro/US outlet adapter to simply raise it up, staggering the heights for better air-circulation.

 

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16 individual 3.2V chargers

 

The charger case connects to each pack using a Centronics 36-pin connector. Each pack has a switch that turns on CellLogs to read the state-of-charge. There’s not much to say, plug it in and turn it on – all green LEDs means “fully charged”. The cells remain in excellent health after 250 charge cycles.

Electrical System

Alan used a 50A magnetic marine breaker for the main power disconnect switch (Blue Sea model #7230). These types of breakers are very rugged and are intended for high-humidity/salt-air use. They are designed for up to 65V-DC and can handle interruption currents up to 7500A making them virtually indestructible in this application. “They start to trip at 62A and with a couple of controller shorts, the CycleAnalyst never recorded a spike greater than 180A before the breaker switched off”.

 

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The on/off keyswitch (metal box) and the main breaker are at the bottom right, the fuse-panel and horn are at the top.

 

The 50A breaker has worked flawlessly and tripped so quickly that the 50A Maxi fuses in the battery packs never popped.  “For around $15, I cannot recommend this breaker more highly”. It is not rated for weatherproof use, so Alan mounted it upside-down to discourage water entry. A 5W / 330-Ohm resistor and pushbutton provide a standard pre-charge circuit to prevent arcing when switching on the breaker.

Both the original Crystalyte and the later Lyen controllers have a feature where the logic is powered using an ‘ignition’ wire separately from the main-rail FETs. This allows the logic to be powered down leaving the capacitors connected but essentially drawing no power. The bike uses this feature to support a kill switch and keyswitch.

The keyswitch (mounted near the controllers) connects battery power from the breaker to the low-amp handlebar kill-switch, which then powers the controller ‘ignition wires’. The key can be turned on and then removed so the kill switch provides convenient on/off control, or it can be carried and used to disable the bike from being ridden away. The keyswitch is made for exterior-grade security systems and easily found on eBay for less than $8.

For safely riding in traffic, Alan wanted lights, turn signals, a horn, and strobed “blinky” lights. He decided to use readily available 12V components powered by a DC/DC converter. A Green Galaxy 48V-72V 120W unit from ThunderStruck Motors supplies 10A to power the 12v lighting. The converter requires both the main breaker and keyswitch in the “ON” position to operate. The 66V system can be hard on switch contacts because of arcing, so the keyswitch drives a relay to power the DC/DC converter. The relay is a 48V unit from a golf-cart lighting conversion kit and operates reliably at 66V DC with no problems (carefully read ALL of the details in the original post before attempting any of these mods).

“I wanted a valuable piece of safety gear – a FIAM “freeway blaster” auto horn – one of the loudest non-air-horns available.” A conventional 12V automotive horn relay is driven by the handlebar button. Since horns of this type are just giant interrupting inductors and the electrical noise spikes are beyond huge, the horn uses dedicated (+/-) power lines to the battery (so the rest of the system is unaffected). A 1N4006 diode is soldered across the horn terminals as a snubber. The horn body must be must be mounted so that it can vibrate freely for maximum loudness, and so is just mounted loosely with a nylock on the mounting stud”

Lights

In addition to conventional headlight, taillight, and turn signals, Alan added daylight-visible strobe lights. “I didn’t want toy LED strobes with replaceable batteries, I wanted 12V you-can-see-me-at-100-yards-in-daylight mega blasters.” The headlight is a generic 4-inch bobber motorcycle unit with a cylindrical “bullet” shape (as opposed to teardrop) that offers a lot of interior room for mounting electrical components and uses a 55W halogen H4 bulb.

 

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A well thought out  front light assembly

 

The rear light is a 6-inch oval Optronics STL72RK LED tail/brake light used for trucks/trailers. The taillight portion is wired to the headlight power. The much brighter brake light portion is not used a brake light but is instead used as a rear strobe.

 

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The tail-light assembly

 

The front strobe is a single round truck side-light with a 2-inch diameter clear lens and 4 amber LEDs. There are a variety of these available, and Alan found the brightest by far was a generic Chinese unit  with four LEDs with individual dish reflectors behind each one [link]. The front and rear LED lights are strobed by an LSC-100B continuous pulsing strobe module [link]. The module is only $5 and about the size of a pack of gum. It flashes four times rapidly, pauses, and then flashes  again, etc.

To get brightness and side-visibility, the turn signals are incandescent 23W reproductions of classic motorcycle units with domed lens. The turn signals are driven by a common 3-pin auto flasher that is tucked inside the headlight housing along with the strobe module. All the lights came with isolated ground wires, except the turn signals which were converted to 2-wire operation (socket not grounded to the frame). “Unfortunately, I sometimes left the turn-signals on after making a turn and so added a dashboard LED.  The LED was too far from my normal line of sight and didn’t work out well, so I finally settled on a small 72-db Piezo beeper that is simply wired across the LED indicator. Much like the clicker in a car, it solved the problem.”

All the front lights are attached to a custom box that is mounted to the head-tube of the frame by two standard  aluminum/stainless-steel saddle-clamps from DX-Engineering. The U-bolts are covered with  heat-shrink to protect the paint. Although the box is fairly inconspicuous, a larger size would have made construction and wiring easier.

For an off-the-shelf motorcycle-style switch assembly, Alan chose the K&S Technologies 9-pin model #12-0055CN.  Although it has a plastic body, it is narrow (which helps the crowded handlebars) and has good quality internal switches. This controls lights, horn, and turn signals…while a toggle on the dashboard controls the strobes.

Brakes

The stock Mundo V-brakes are upgraded front and rear to Avid BB7 185mm disc brakes. “They work  great and the easy adjustment certainly lived up to the reviews. This was a huge improvement, and well worth the  trouble.”  However, the BB7 185mm does not install properly in the rear using the special Yuba adapter which is made for a 160mm disc. Here’s a link to a work-around that Alan used.

Other

The front motor uses two stacked Ampedbikes torque-arms (1/4” total thickness) on one side. These are very cool and will align with almost anything; the teeth on the inner disc are tiny to allow fine adjustment of the arm angle, but you can also flip the disc over to get a ½ tooth rotation for ‘in-between’ cases.

The shaft flats on the front motor are only 17mm in diameter and the drop-outs on the Mundo are the common 14mm, so the 1.5mm shaft shoulder could easily damage the drop-outs when tightened down. Thin stainless-steel washers are placed inside of the dropouts to catch the shoulder and spread the load over a larger dropout area.

Mounting the rear motor was a nightmare because of the oversize Mundo 14mm rear axle. At the time of this build, [ES member] Kiwi had not yet designed his spiffy rear torque-plates for the Mundo V4. The Kiwi plates are highly recommended, but here is the method Alan used instead. Front and rear  torque arms have been overbuilt, but the small extra cost and effort was worth it for the peace of mind. After 7500 miles, they haven’t budged, even with 1700W peaks per motor.

To help make pedaling possible at higher speeds, the crankset has been upgraded from the original 42-32-24 to a Shimano 52-42-30. With the rear motor fitted with a DNP 11T-32T freewheel, pedaling cadence is comfortable at 30-MPH and workable into the upper 30’s.

At recent addition is a temperature sensor on the front motor that uses the Cycle Analyst V3 for power rollback on overheating. Because of the difficulty of installing a sensor in the BMC motor and pulling new axle wiring, Alan tried an experiment that involved drilling a small diameter hole lengthwise in the axle. This allowed him to position a thermistor deep inside the motor. Although not as quickly responsive as a sensor on the windings, it gives reliable results where temperatures rise slowly and a minute or so of lag is acceptable. This has worked out well and required no bike down-time for the upgrade.

All custom metalwork used 1/8th inch thick 5052-T6 aluminum sheet (slightly thinner 3/32-inch should be adequate and easier to cut and form). Cutting was done with a common tablesaw fitted with a $70 Freud LU77M010 non-ferrous blade which gave clean effortless cuts. A recent post suggested the more affordable Oshlun SBNF-120120 would work just as well ($55 on Amazon). Simple pop-rivets fastened the pieces together and nut-serts/riv-nuts provided threaded mounts.

Alan scratched the screen of his original Cycle Analyst with just a casual wipe when it was covered with trail grit. When he upgraded to the V3 he picked up a ZAGG “Invisible Shield” screen protector kit made for a smart-phone screen. Trimmed to size, it works great! Highly recommended.

 

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The Abus wheel-lock

 

Although he carries an Abus hardened lock and chain,  Alan wanted a more convenient lighter duty lock as well. “For some time I wanted a Dutch-style frame-lock so I could just run into a store quickly. Since the bike is about 150-lbs and 6 feet long, it would be hard to lift or carry away. I chose the ABUS Amparo 48550 SP/LH, which has a key that can be removed when unlocked.”  This lock is a hit. It’s super easy to use, and although it’s not suitable for high security, it has its place and fills many of Alan’s frequent locking needs very nicely.

Final Assessment

“In general. I couldn’t be happier. This thing is super fun, climbs steep hills like crazy, and the 2WD has gotten me home without incident, even with a couple of controller failures. This bike is heavy and perhaps more like a moped, but is still easy to pedal on the flat. I’m happy to have the turn signals on a daily basis, and the high power blinky’s have been a spectacular success for getting the attention of car drivers. It was sometimes hard not to hurry the build and get riding, but the result has a nice production feel that was worth the extra attention.”

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I usually need more pics than what builders originally posted, but Alan has provided quite a few more pics than what I could fit in this article. To see all of the pics, and read even more details about this amazingly professional Mundo, go to his build thread here.

Philistines Yuba http://endless-sphere.com/forums/viewtopic.php?f=6&t=30679

Kiwi’s Yubas http://endless-sphere.com/forums/viewtopic.php?f=6&t=26413

kiwi’s torque-plate thread (Yuba conversion parts) http://endless-sphere.com/forums/viewtopic.php?f=31&t=31881

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Written by Ron/Spinningmagnets, November 2013

Grew up in Los Angeles California, US Navy submarine mechanic from 1977-81/SanDiego. Hydraulic mechanic in the 1980's/Los Angeles. Heavy equipment operator in the 1990's/traveled to various locations. Dump truck driver in the 2000's/SW Utah. Currently a water plant operator since 2010/NW Kansas

2 Comments

  1. This bike looks so cumbersome and it wouldn’t be legal on Australia!

  2. Great to see those pushing the boundaries of electric bike design. There is no reason to limit oneself to arbitrary design classifications except by those imposed by law. Making a variety of designs helps to ensure the best design for the need is available.

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