My Mongoose Hatchet DS E-Bike

[Russell]

This is my second effort at building a comfortable commuter e-bike, my first is detailed here; http://endless-sphere.com/forums/viewtopic.php?f=6&t=38759
The Schwinn turned out well enough but it was a tad small for me. I sold the Schwinn after converting it back to original condition then purchased a Mongoose Hatchet 29" dual-suspension mountain bike from Walmart. The Mongoose is the same frame size as the Schwinn however being a 29'er it is larger overall with a longer top tube and wheelbase. It fits me nicely Here it is in original condition;

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...and after a few months of ordering parts, waiting, installing, pondering, ordering more stuff, and more fitting parts here it is

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Except for one quibble I have with the BPM motor (it can get noisy) the bike turned out great, it is comfortable, handles well and pedals nicely to boot. Right now I'm using a pair of Turnigy 6S 8000mAh Nano-Tech packs for power which yields a top speed of just over 26 mph and a range of perhaps 18 miles at 20 mph with light to moderate pedaling.

-R

[Russell]

Some more pic's:

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-R

[Russell]

WooHoo...49.6 MPH

Down a hill of course

Not just any hill, but the steepest I know of in the vicinity, with a rise of 130 feet (13%) over one 1,000 foot stretch of road (per Google Earth). One of my regular routes takes me closeby the hill but I don't usually detour to give it a go. The last time I did was with my Kona Smoke 2-9 equipped with a little geared motor from E-BikeKit and a 2C max 15S LiFePO4 battery and 20A controller. On that occassion I topped the hill at just over 7 mph...then turned around and screamed down it hitting 48 MPH. This time with the Bafang BPM I crested the hill at 10 mph on 12S LiPo with the controller at 20.5A max (adjusted down from 26.5A of the initial build). In both instances I pedaled heavily.

On a general note; so far the bike has performed well, though I have not yet used it to commute to work. The only changes I've made is to switch out the saddle and the aforementioned adjustment to lower the peak controller current. At 1,200-1,300W the BPM was just too eager off the line. Now with 900-1,000W on tap acceleration is moderated, and so of course is hill-climbing. I use the cruise feature nearly all the time on this bike and the drop in speed on grades is more noticeable at the the lower power level. I am impressed with the Turnigy Nano-Tech batteries; voltage sag and heat generation is minimal and balancing appears to be optional as the cells charge up right where they started. As I stated before the only thing that bothers me is the "clack-clack-clack" noise from the clutch in the Bafang when cruising at light load and near the no-load speed. The noise is annoying and makes the otherwise stealthly bike less so. I'm thinking of replacing the motor or perhaps locking the clutch.

-R

[floatingdog]

You're bike looks great. I haven't kept up with you. A BPM and it is on the rear wheel! I like it. Your torque arms look perfect for your rig. I may copy you.

I'm still running your triple Fatpacks on my BPM. It is a code 13 and is only good for about 18mph on the flats. I did hit high 20's on a downhill. I've been tempted to go 12s or 14s Lipo to get up over 20 without killing my little 6 FET eCrazyman.

No clacking on my BPM, but I have no cruise control and mostly just have it at medium, full, or no throttle.

[motomech]

Russell, rather than replacing the BMP, an option might be to install a mini on the frt. and make that your prime mover as an pedal assist and use the BPM for fast squirts across intersections and climbing, not unlike my set-up, just reversed.
I know you know this, but for anyone dropping in;
My rear motor is the fast wind "Cute" Q100 in a 24" wheel running on the stock KU63 controller @ 12S and I see max/Watts of 650.
I am a "full sized" rider and gross bike/rider all-up weight is 300 lb.s and top speed of the rear system is power limited to the low 20's mph, but with my current 11T/44T combo, I can pedal assist up to 25 mph. On a down-grade, the over-run of the fast wind will still add 200 Watts @ 30 mph.
It is a poor climber at this weight and will not climb my 10%, even with all the assist I can provide. Still, this is a very good assist system and in the morning I leave the frt. aux Mxus switched off to force me to pedal.
With the MXUS/Lyen 22 A controller combo, I see XWatts in the range of 1000, so in combo of both motors, the C.A. shows Max Watts around 1650.
The fast wind Cute helps to pull the MXUS up into higher top speed range so I see a no-pedal top speed with both motor engaged of 26-27 mph.
The 10% hill is no problem and I can maintain 15 mph or so climbing it.
With a Zippy 12S 5000 mAh 15C pack, sag is 2 Volts, but with a same sized Turnigy 20C pack, it is only 1V.
I am very happy with this set-up, but it would be better if the high powered motor was on the rear, as the MXUS/Lyen controller combo up frt. is a bit "twitchy" and will spin the tire if I am not careful.
I'm still not entirely happy with my dual throttle combo of half twist side-by-side with a thumb, as it is slightly awkward to use. I am going to try and re-adjust them today, but I may go with 2 half-twists, both rotating forward.

[Russell]

You're bike looks great. I haven't kept up with you. A BPM and it is on the rear wheel! I like it. Your torque arms look perfect for your rig. I may copy you.

I'm still running your triple Fatpacks on my BPM. It is a code 13 and is only good for about 18mph on the flats. I did hit high 20's on a downhill. I've been tempted to go 12s or 14s Lipo to get up over 20 without killing my little 6 FET eCrazyman.

No clacking on my BPM, but I have no cruise control and mostly just have it at medium, full, or no throttle.

One reason I chose the bike I did was it had the nice flat steel rear dropouts which makes installing the torque plates a breeze. I like this solution far better than a conventional torque arm held on with hose clamps.

It's good to hear the Fat Packs are still working for you. I looked back and saw I assembled the pack over 3 years ago (April, 2009). It's too bad they are so expensive now because they are quality batteries. Still nowadays it's hard to beat the price, weight and power density of hobby LiPo.

I was juggling controllers a couple of weeks ago and dug out my Ecrazyman 6-FET sensorless controller. Mine has 60V FETs and 63V caps and works fine with 12S LiPo. I tossed it on my other bike for a few rides but ended up returning to a sensored controller.

It's too bad my BPM's clutch is noisy because it's otherwise a fine motor. I'll have to open it up some day and take a look at it.

-R

[Russell]

Motomech,

I would not want to add a front motor to the bike with the BPM on the back but I am still considering dual Cutes. I'm thinking about a slow Cute in back with the controller activated by a pedelec sensor and a fast Cute up front controlled by a throttle.

The second option I'm considering is to go with a 9C up front. Since I use the motor all of the time on this bike I don't need the freewheeling ability of the BPM, except of course to fly down hills. I also enjoyed having more power on tap but I'd like it to come in more slowly which would happen with a DD motor compared to the geared motor.

-R

[floatingdog]

It's too bad my BPM's clutch is noisy because it's otherwise a fine motor. I'll have to open it up some day and take a look at it.

I've never noticed the noisy clutch on my BPM (code 13). Perhaps some other BPM owners will weigh in or you can PM some of them. It may be that I just never hold the throttle near no-load. I'm guessing the cruise control may hold it there when little assist is needed. Does the problem go away if you don't use cruise control? If the cruise control is implicated, perhaps there is something configurable in the controller to add a little extra hysteresis so that it doesn't fluctuate the power setting as frequently. E.g., the speed has to change say 1/2 mph instead of 1/10 mph before the controller adds or decreases power.

[Russell]

I use cruise control pretty much all of the time on this bike. The clutch makes the clacking sound whenever it is lightly loaded, like when cruising on level ground, and it's especially loud when passing through the top speed. When there is more load, like when going up any kind of grade, the noise goes away. The Heinzmann geared motor I owned briefly made a similar sound. It was also very noisy when near the top speed when the clutch engaged and disengaged due to changing loads (pedaling or down a grade).

-R

[Russell]

I had already tried two controllers on the bike, a KU93 9-FET set to 26.5A and an older "universal" 9-FET 20A controller, both from BMSbattery, but today I installed a "Lyen" 6-FET 4110 Mini that I picked up from an ES member a few months ago to see how it performed. Right away the acceleration I enjoyed with the first controller was back...as expected since the Mini peaked at 27.5A during today's trip(1326 Wp). With the added power I couldn't resist having another go at the 13% grade hill that's just a bit of a detour off my favorite route. Today I crested that slope (spinning furiously) at just over 14 MPH compared to 10 MPH on the 20A controller (down the hill I only managed to hit 48.5 MPH ). I do believe the "clacking" noise from the BPM's clutch was less pronounced, especially when on cruise control (which I enabled by shorting TP 'cr' to gnd). The clutch still makes a racket when passing through about 27 MPH at full throttle but I think that is even a bit better. I'll keep this controller on the bike for a while to get a better feeling for it's performance but so far I'm happy with it.

-R

[Russell]

It feels windy all of the time at 25 MPH

I don’t use this bike much preferring instead to ride my Jeep E-bike with it’s little 250W Bafang. With that bike I pedal continuously and with moderate to heavy effort so I get a lot of exercise at a pace I probably couldn’t match even in my youth on a road bike. It’s a lot of fun. This Mongoose is a different animal and it’s closer to what the majority of folks on this board build for themselves and even weak by many poster’s standards. It’s sorta fun too but in a different way. But like I said it’s not getting much use.

I originally built this bike just for the heck of it…and to perhaps use to commute to work. Unfortunately I start early, getting up before the sun, and I’m not inclined to rise even earlier to ride the bike to work. So now on weekends I generally go out for a long ride on my Jeep bike then after charging the battery I sometimes go for a shorter spin on the Mongoose. Since I use higher power with this bike and don’t pedal much I use about 40% more juice with this bike than the Jeep for the same average trip speed. That limits my range using a 12S 8Ah LiPo pack. It also limits my speed and I’ve been keeping it under 20 MPH so I can comfortably make a favorite 17.5 mile loop.

Today I wanted to see what it was like to ride this bike like a scooter with virtually no pedaling at speeds averaging 25 MPH. Again that may be sedate by some folk’s standards but it’s far above my normal ~18 MPH average trip speed. The ebike.ca simulator says the BPM should consume 30 Wh/mi at 25.0 MPH therefore I would need 525 Wh total to complete the 17.5 mile loop. For the ride I combined two 12S LiPo packs, an 8Ah and a 5Ah, to give me a maximum of about 580 Wh. Just last week I rode with the combined packs on the Jeep and consumed them completely on a 52 mile trek using 575 Wh.

Averaging 25 MPH turned out to be a bit harder than I figured. I used the cruise feature to hold the bike close to 25 but of course hills and slowing for stops impacts the average speed. I pedaled only up grades to keep the speed up but in the end I averaged 24.2 MPH over the 17.5 mile course. At 14 miles the motor felt slower as the battery weakened. At the end of the ride though any fear I had about running out of power proved to be unfounded as the wattmeter said I used just 424 Wh of power, which coincidentally calculates to 24.2 Wh/mile. The motor felt cooler than on slower rides though I attribute that mainly to the low 70’s temperatures. The controller too was barely warm, but then I’ve never had a controller get hot on me.

In the end the bike does what it was built to do. The 27.5A controller, 1,300W peak power and the torquey nature of the BPM geared motor means the bike can indeed be ridden like a scooter. Still, for cycling fun I’ll stay with a little motor on a bike that’s enjoyable to pedal.

-R