Our direct drive bakfiets cargo bike build.

[Ira]

Hi, this is my first thread, although I've been lurking and searching for advice for a couple months.

This is our ebike, along with a tumblr of the build. http://electriccargobike.tumblr.com/
This thing has been our family station wagon for a few years, but we've got to the point where a little more power and range make a big difference, and added the assist. Let me know what you think!

 

[hjns]

Nice. Looks like you don't use any torque arms. Get two of them quickly or risk loosing the motor from the dropouts...

 

[Ira]

Nice. Looks like you don't use any torque arms. Get two of them quickly or risk loosing the motor from the dropouts...

there is a torque arm on one side. the axle is oversized and has flats on it, which fill the dropout entirely. it fits so snugly that i had to file off the paint. it seems unlikely there would be rotation unless the dropout is deformed.

edit - i don't meant to sound like a know-it-all here, as this is my first attempt. should i be worried about torque damage to the dropouts, despite the single sided torque arm?

 

[melodious]

Congratulations on your new Eride! One criticism from my part is the wires coming out from the axle needs to "drip looped". This prevents water from entering your motor which can cause corrosion further down the line.

This is a drip loop...

 

[Ira]

melodious, excellent, thank you. as i said before, the axel is keyed directionally, so the wire is either "up" (the way it is currently oriented) or "down". i should probably orient it the opposite way, huh?

 

[Ira]

I should get on that drip loop ASAP, because my wife is off-roading in the snow as we speak!

 

[amberwolf]

there is a torque arm on one side. the axle is oversized and has flats on it, which fill the dropout entirely. it fits so snugly that i had to file off the paint. it seems unlikely there would be rotation unless the dropout is deformed.

edit - i don't meant to sound like a know-it-all here, as this is my first attempt. should i be worried about torque damage to the dropouts, despite the single sided torque arm?

Depends on the torque you put thru it, and if you use regen braking. It's possible that nothing will ever fail, but I prefer to be pessimistic where it concerns having my vehicle fail while on the road somewhere. (has happened too much).

Using the latter means the axle will be rocked back and forth, as no fit is ever quite perfect, and each cycle will slightly enlarge the gaps, increasing the rocking, until:
http://www.endless-sphere.com/forums/viewtopic.php?p=545492#p545492

Even with torque arms, it's still possible to spin the axle in the dropouts. Personally, I prefer at least two torque arms, if going higher than 500-700W depending on the torque load. Some will say 1000W, or higher. Depends on axle and dropout and torque arm material, torque arm thickness, axle flat size, torque you put into it, etc.

I also spun a geared hubmotor in a steel front dropout, at around 1200W peak, IIRC, during a startup from a stop. Tore up the wiring some. I suspect the axle nuts were not fully tightened, though.

The torque load can be higher for longer durations if you have a heavy bike, or cargo loads, or heavy rider (or all three). Crazybike plus me is around 300lbs, much more with cargo on it, and up to double that with heavy cargo plus a trailer full too.

 

[Samd]

Hey thanks for catching up after we metup via Instagram! Love this build. Need some of those torque arms for my monster build dual drive dual suspension project!

I ended up using a geared Ezee at 600 watts on a rear 26 inch cargo trike. The takeoff torque is awesome with three kids up front.
I upgraded the tyres to Maxxis Holy Rollers, best thing we did apart from elec drive. The combination of wall strength and flex means that the rolling resistance is low but you can hit something hard with a wheel and not break your spine - or you kids. Very forgiving on the frame.
Cheers,
Sam

 

[hjns]

Hi Ira,

As Dogman said, better safe than sorry. There is absolutely no harm in adding a second TA, and it will definitely be much stronger than a single TA. Even though your power is limited, with a fully loaded bakfiets there are considerable forces playing on the axis of your "poor little" hubmotor. However, at this moment I would agree turning the motor around and create the drop loop ASAP. Snow will melt into the motor, leaving the water inside. Not good.

I love the canopy to protect the kids from the weather. It also makes for a more streamlined aerodynamic form, which is very good.

 

[amberwolf]

Fixing the drip loop will help, but keep in mind that water will get into the hub no matter what you do to it, even though it will be much less with the drip loop. See Kingfish's rust / repair thread for some details and links to a video by Justin LE of ebikes.ca about the problem.

 

[Ypedal]

That and the amped torque arm imo is not that great, it's too thin and will cut into the axle allowing it to spin anyway... thicker is better, and if the amped units are all you got, i'd double them up, at least.

better yet, is a pinch type axle retainer, nut and bolt that clamps on the axle flats, then the axle nut for extra insurance.. considering kids in the box..

cool rig tho !.. i plan to make myself one soon.

what voltage/amps are you running on it ?

 

[Ira]

Thanks for the torque arm suggestions. I'll add one on the other side as well. The large 200mm disc rotor puts a bunch of additional force on the dropout, so it should help on both counts.

That and the amped torque arm imo is not that great, it's too thin and will cut into the axle allowing it to spin anyway... thicker is better, and if the amped units are all you got, i'd double them up, at least.

better yet, is a pinch type axle retainer, nut and bolt that clamps on the axle flats, then the axle nut for extra insurance.. considering kids in the box..

cool rig tho !.. i plan to make myself one soon.

what voltage/amps are you running on it ?

I'm using the stock AmpedBikes kit - 36V 12AH SLA battery.

 

[Ira]

Can anyone recommend a better way to convert 32V dc to 6V ac?

this does power my front and rear lights, but feels a little kludgy...

 

[agniusm]

Congrats. Nice, clean looking bike. I would look into dropout thing. After all when babes on board, no compromise should be made for safety.

 

[Ira]

agniusm, your cargo bike project looks ambitious! looking forward to following it. i ordered a second torque arm today.

 

[agniusm]

Yeah, i know. I don't know why i get into complicated projects all the time
Good to hear about torque arm. What is your front tire? I just can make 'marathon' from photos

 

[Samd]

What's really important is the thickness of the torque arm. There's a good thread here *somewhere* where Justin Le destructively tests many using a large torque bar and measures the amount of torque in Newton Meters to failure. Regardless of shape, arms thinner than about 5mm failed as the eye shape that goes over the hub's axle would smear out of shape.

 

[Samd]

If you have the time, read this thread. Proper scientific approach to torque arms. http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=14195&p=232469&hilit=front+fork+test+torque#p232483

 

[veloman]

My single amped bikes torque arm held my slow wind 2810 9c in a 26" front wheel at 1700watts with no sign of slippage or damage to the dropout area at contact. That's with 12mm axle flats - the small ones.

I did install a homemade torque arm on the other, as it's now capable of 2400watts.

 

[Samd]

I like the ampedbikes L shape - similar to dogmans. Any chance you could tell me the thickness? You do get th benefit with DD hubs of lower takeoff torque...

 

[full-throttle]

Can anyone recommend a better way to convert 32V dc to 6V ac?

Most likely it doesn't have to be 6V AC.
Something like this should work.

 

[Samd]

Does it have to be AC out? I think these car converters will take a lot more than twelve volts in maybe? http://www.gotwind.org/diy/stepper_motor.htm

 

[Ira]

I like the ampedbikes L shape - similar to dogmans. Any chance you could tell me the thickness? You do get th benefit with DD hubs of lower takeoff torque...

i'll measure it next time i have the bike out. i ordered a second for the other side. it's not 5mm - more like 2-3. It's laser-cut stainless, so very precise and harder than the axle material.

 

[Ykick]

I like the ampedbikes L shape - similar to dogmans. Any chance you could tell me the thickness? You do get th benefit with DD hubs of lower takeoff torque...

i'll measure it next time i have the bike out. i ordered a second for the other side. it's not 5mm - more like 2-3. It's laser-cut stainless, so very precise and harder than the axle material.

2.5mm thick for the ones I have here. Definitely thin for powerful systems but I've never had issues or ANY signs of deformity running under 2kW front or rear DD motors.

 

[Ira]

Yeah, i know. I don't know why i get into complicated projects all the time
Good to hear about torque arm. What is your front tire? I just can make 'marathon' from photos

they are schwalbe marathons. excellent touring tire, very puncture resistant.