"girlfriend's green meanie" front 350w MAC Trek build

[neptronix]

Yes, we now have 3 eBikes in the stable, full time..

Early on, when i was just starting out with this eBike business, i picked up a $500 used "ecoBike elegance" for my lady. She'd not been into bike riding for a while and i wanted to really reduce our gas usage by going to the store together.





Now this was fine and dandy, but when i got my MAC and fell in love with it, the 250w ecobike just couldn't keep up.
I figured we could have made $ selling it ( got a great deal on it ), rather than upgrading it, so we did.. and we made $150 on the deal.

Plans for a higher power bike for her, that could keep up with my 8T MAC fairly well, ensued in record time.

We picked up a green Trek we found on craigslist ( $90 and just needed a little tune up! ) and later ordered the 350w MAC motor in a 700c wheel.
The 350w MAC motor appears to come in one wind, sorta a 9T equivalent to the rear, and does 22-24mph on a 700c wheel. It's a pound lighter than the 500w MAC, but not smaller. It seems to handle a pretty good level of power constant without getting warm ( around 500w average, with peaks of 24A / ~1000w ).





Initially, ampedbike torque arms were ordered mistakenly. They were very loose on the motor and would have been useless. So i set to making some torque plates.

Took me a very long time to make them. I have really wimpy tools. A local friend ( tom tom on ES ) let me use his angle grinder to cut the basic shape.. the rest was all $$$ dremel bits, and sanding by hand.

Luckily the fork is steel, so i didn't have to make the plates super strong. But i kinda overkilled them anyway.. why not





So here is the ( mostly ) finished product! the batteries and controller hang out in the rear topeak bag.



.. which is of course Lipo.. see the 4mm bullet connector at the end of the 9FET controller
We can fit about 14 5S or 6S 5AH packs in it, but often we just stick in a 10AH/10S brick.

Controller is set to pull a maximum of 24A, and the phase amps are set to 2.0x that value. It doesn't pull too hard from a stop, it really forces you to pedal along initially, then picks up speed in the mid-range. Downside is that it's rather anemic on hills or in a head wind. I will up the amps a little when i know 100% that the torque plates are doing their job.

So far, so good! it's quite a bit more efficient than my 8T mac on 36A/36V due to the lower speed and the fact that it kinda forces you into putting more pedal effort in. This bike is exactly what i had in mind when i set off to build my first eBike ( the 250w was just a dog on 36v and the top speed of 18mph sucked! ) - more like a bicycle than a slow motorcycle. The top speed of about 23mph is really bicycle like.

The 350W MAC motor is a little spendy for a first time bike build, but i'd say it's worth it if you want pedal assist and just a wee bit more speed than you'd normally be able to muster on a nonpowered bike. The weight of the motor could be cut down a little, but it's not too bad at 9lbs.

[veloman]

I have that same saddle on my girlfriend's road bike that I let her use at my place. She has 3 bikes she uses at my place, though lately it's been the Proflex ebike.

I need to get her onto a faster motor, as 18mph slows us down. She said she wouldn't mind more power on the hills than the mxus 500watt peak motor. Little by little I'm getting her to a real bike, somewhat.

It's easier building an ebike for your girl, eh? Weigh less, doesn't need as much power.....

[motomech]

Nep.,
Is the axle on the Mac larger than the 9 mm axle used by the mini[MXUS]?

[neptronix]

veloman, sorry for the late response. Yeah, her expectations of what an eBike should be are quite lower. We have since put a falconEV bag on it because the rear rack was clunking and thunking too much for our tastes. Also switched out the controller for a cell_man EB3 9FET because the old EB2 was making a racket at full speed. MACs just run so erratically on those.

Nep.,
Is the axle on the Mac larger than the 9 mm axle used by the mini[MXUS]?

For the rear 500W, it is the same diameter as the rear MXUS.
I don't know about the front - but i do know that the axle is narrower on the front MAC versus the rear MAC. I believe it is a difference of 1mm.

[motomech]

I really like that motor and think that will be my next "upgrade".
My Dirt Jumper II forks look much stronger that the wimpy looking alum. chain stay on my Edge.
I have a C7225-NC 36-72V 25A controller, 6xIRFB4110 mosfets, from Ebike CA laying around,
any idea if it would mate well with the 350W Mac?

[neptronix]

The forks on that bike are steel. The dropouts are particularly thick. The torque plate is just there for extra assurance and this isn't a lot of power. I've bumped it up to 1000w but the cromoly forks *do* flex a tiny bit under this use.

This is as much power / speed as my lady can tolerate due to her distance perception issues. So this bike is basically as good as it's gonna get for her.

Do the rear 500w. Trust me, dude. You will not regret it. Front motor is a mistake. It's for low power and low expectations. Everyone who does front motor ends up doing rear motor. Aluminum suspension forks are not designed for the twisting loads that a hub motor puts on them at all. They might look tough, but they are not. Ask anyone who's had their front wheel fall out from beneath them. There aren't many possibilities for securing the torque on those.

Think about how your fork flexes under the load of braking with a disc brake, particularly with a 185 or 203mm disc. The forces that a hub motor can put out are beyond that, the more watts you pump into it.

Another problem with front motors is that these eBike hubs often have poor alignment of the disc brake mounting holes. I've had a few make a perfectly straight rotor wobble, making using disc brakes on that motor useless. Luckily all my hubs have been rear, so it doesn't matter much.

OK, have i pumped you up with enough anti front motor propoganda yet?

The rear 500w motor is 1lb. heavier but produces quite a bit more power. Trust me when i say you'll end up wanting more power later, when you know your motor can take 3 times what it's rated for good periods of time

But to answer your other question, the 350w front does 23mph on 36v, yes.

[dogman]

Shocking to see you own a frontie. But there are some things that are nice about front. On my commuter, for instance, I get to keep the original cassete geared rear wheel. Nothing wrong with a front motor for street on steel forks.

I like it, I did not know you could get a Mac in frontie ( I had seen BMC front), or that it was disc ready. A small market niche, but nice to see it filled. I've been thinking about a small gearmotor on the front of my longtail. But now I see I also have the option of a bit more powerful front gearmotor. Maybe never happen anyway, but the fantasy is to take a month off sometime, and ride all over Colorado on the longtail. So riding all the passes, I'd need more than one motor for the uphill parts.

[neptronix]

Shocking to see you own a frontie. But there are some things that are nice about front. On my commuter, for instance, I get to keep the original cassete geared rear wheel. Nothing wrong with a front motor for street on steel forks.

I like it, I did not know you could get a Mac in frontie ( I had seen BMC front), or that it was disc ready. A small market niche, but nice to see it filled. I've been thinking about a small gearmotor on the front of my longtail. But now I see I also have the option of a bit more powerful front gearmotor. Maybe never happen anyway, but the fantasy is to take a month off sometime, and ride all over Colorado on the longtail. So riding all the passes, I'd need more than one motor for the uphill parts.

Yeah, the front motor was picked only because i wanted to keep the original rear gearing and not hack the bike up - keep it nice and clean. The power level will never go up from here. We also may save a little bit of weight by using a cassette and not a freewheel in the rear.

Dude.. you like low turn count direct drives, dontcha? just get a magic pie . You can forget the dual drive idea with that kind of power. Even on a 24" rim, it will be a monster high efficiency climbing machine. It's a super underrated motor. It really beats the tar out of my old MXUS, which is similar to what you run.

Do check my 20" magic pie build thread and put a reply in there if you are interested tho, to prevent this thread from getting too crowded.