GMAC Motor and Pinion Gearbox

drewberz

Active Member
Has anyone worked with either the GMAC or a Pinion drive to make a project e-bike?

I would love a low maintenance, long-distance, efficient commuter built as light as reasonably possible. Parts availability and reliability from Bafang are a concern to me so I'd rather stay away from them. Considering the Hub Drive AND Pinion vs. MidDrive and IGH debate, I think the former would be better in my case. The upside is that my bike can get a rear wheel swap and it's back to being a 'normal' bike.

Before I was considering drop-bars only, but those options are really limited so I think I'd do a Jones H Loop Bar setup. Some features I am considering are:

1. Belt drive
2. Large capacity battery pack or capability to increase easily
3. Built lighter than 50lbs. (Not sure how possible this is)
4. Capacity for 32-50c tires with fenders
5. Eyelets throughout
6. Frameset material (whatever is reasonably light, but still durable to haul me+light gear+bike, so ~280lb. total load)
7. Non-suspension carbon fork
8. 28mph limit

I was thinking:

Priority 600 or Steven C12 Lite or Rose Active Pro Pinion 12 or custom???
GMAC Kit So high-powered hub motor, with regen and a 21700 cell battery pack

This would be a $5,000+ build, but I think it'd have a lot of utility.
 

Ravi Kempaiah

Well-Known Member
While in theory it is possible,here are the challenges you will have to overcome.

Those frames are not built for E-bike loads and may affect the frame warranty.
Dropouts are certainly not built for handling the torque of a well-built motor. You may have to go for a very low powered motor.

Considering the Hub Drive AND Pinion vs. MidDrive and IGH debate, I think the former would be better in my case.
Pinion drive is really nice! I had the opportunity to try one a few years ago and it made total sense as the weight is distributed in the center of the frame and it has equal build quality and service life of that of Rohloff.

The issue with your build is, you will lose the torque sensor. Where are you going to mount the sensor? Will it be a throttle control bike?

Custom frame to fit the Pinion drive and single piece of the Pinion (if you can get one with warranty) will run upwards of $2.5K

Add a motor with torque sensing, wiring+cable and matching custom battery with wiring that fits perfectly and doesn't look like a rat's nest - add $1500 to $2000.

Then lights, rack, fenders, charger etc. This could be a nice senior design project for a Bachelors student. You would be much better off getting a Giant QuickE and adding a Rohloff to it.

Or convince one of the EU manufacturers: Kettler or MTB Cyclotech to ship you one:
https://www.kettler-alu-rad.de/de/de/index/e-bikes/velossi-prototyp.html

Tout Terrain has a demo model n sale: https://tout-terrain.de/en/the-products/factory-outlet/482/metropolitan-cs-express-select?c=167

Here is a clever idea. Get a nice Steel Frame surly or salsa frame that can accept Gates drive/Pinion and then put a de-restricted BionX-D series drive (this has an in-built torque sensor).
 

drewberz

Active Member
While in theory it is possible,here are the challenges you will have to overcome.



Those frames are not built for E-bike loads and may affect the frame warranty.
Dropouts are certainly not built for handling the torque of a well-built motor. You may have to go for a very low powered motor.
I definitely don't want a low powered motor. Certainly high torque given where I am with lots of hills and how much I weigh.


The issue with your build is, you will lose the torque sensor. Where are you going to mount the sensor? Will it be a throttle control bike?
Couldn't it be a cadence/speed sensor? Grin offers one that would work on the crank spider, but this one would have to be custom fab'ed. Not ideal, but sounds like you can configure the programming to it doesn't just give you a constant power output at a given speed. I would have to take a look at the existing Pinion+Hub motor models on this.

And no throttle. I want it to be a legal bike so in case of an accident I can say I was riding assisted at 28mph or less and thus was abiding by the Class 3 classification.

Custom frame to fit the Pinion drive and single piece of the Pinion (if you can get one with warranty) will run upwards of $2.5K
You know, this may just be the way to do it! Sounds expensive but if you can build something that truly lasts, then would be a wise decision. Of course, this means liquidating my current bike and selling early than I had initially planned.


Then lights, rack, fenders, charger etc. This could be a nice senior design project for a Bachelors student. You would be much better off getting a Giant QuickE and adding a Rohloff to it.
Rohloff sounds tempting, but it just doesn't make sense to have the range of gears. Something like the Pinion 1.9XR I think would make more sense. They claim the Pinion drives can withstand 250NM of torque. I'm assuming that's human+motor.

Or convince one of the EU manufacturers: Kettler or MTB Cyclotech to ship you one:
https://www.kettler-alu-rad.de/de/de/index/e-bikes/velossi-prototyp.html
They use GoSwiss, and I want to stay away from bankrupted companies for the sake of parts supply down the road.

Funny enough, I saw this one and their others shortly after I posted this. Similarly, it has a Bionx (bankrupt now) motor (maybe the parts are generic enough?) but also it's not a good size for me, being 6'3".

Here is a clever idea. Get a nice Steel Frame surly or salsa frame that can accept Gates drive/Pinion and then put a de-restricted BionX-D series drive (this has an in-built torque sensor).
As best I can tell neither looks like they offer a Pinion option.

I like both of these as a starting platform. They are both steel too and can take a big load:

Scrambler Xplore GT
City Xpress GT

Thanks for all your ideas Ravi! I need to do some more digging 🙃
 

indianajo

Well-Known Member
I definitely don't want a low powered motor. Certainly high torque given where I am with lots of hills and how much I weigh.


And no throttle. I want it to be a legal bike so in case of an accident I can say I was riding assisted at 28mph or less and thus was abiding by the Class 3 classification.
The GMAC from ebikes.ca was a high speed winding. Thus low torque. I ride 72 hills on my weekly commute, I use a geared hub motor. The DD hub motor I had before (like the GMAC) used about 50% more electricity on all those hills. With 60 lb supplies & tools my outbound gross weight is 300 lb.
I don't understand the obsession with carbon frame for an ebike. You sound male, you weigh presumably 150 lb or more, the motor & battery weigh 16 lb or so. What is the problem with a 60 lb aluminum frame + drive? I lost 60 lb of lard with a 75 lb steel bike after I quit working. Most North American males could stand to do the same.
Carbon fork is definitely incompatible with front drive bafang geared hub sold by ebikes.ca, and it won't smooth out the bumps of going 28 mph either. 32 mm tires are also bump transmitters. Only people that live in Germany have pavement smooth enough to ride 28 mph on 32 mm tires without suspension IMHO. I use 2 " (56 mm) and it is rough enough to be annoying with no suspension at 10 mph. I do hit 30 mph peaks downhill, but only on good pavement hills.
With hub drive I'm already up to 5000 miles on my chain without maintenance or symptoms. What's wrong with 8 speed chain? Yeah, 11 speed chain is a hassle, 1000 miles per, according to road bike review. So why not put the extra speeds on the front sprocket? You can't do that with belt drive. I have 24 speeds with my 5000 smile endurance chain, 3 x 8 speeds.
As far as maintenance hassle of a bafang hub, you use them up and throw them away. You don't maintain them. $200-300 for a motor, what's the problem? I've got 3000 miles on my ebikeling geared hub motor, no symptoms yet, and the wiring was compatible with the 1000 W DD hub I got for $189. With customs charges going through the roof I've already stored the replacement hub motor + controller + brake handles in the garage. Unlike a battery, a hub motor won't age. The capacitors in the controller will, but I replaced those in the ebikeling motor a month after I installed it. The OEM ebikeling electrolytic capacitors were **** grade and sparked the battery connector every time I plugged it up. You can buy 10000 hour life @ 105 deg C capacitors at farnell or digikey, manufacturers love to limit the life of their product with **** capacitors so you'll buy a new device in 2 to 5 years.
The battery is where $700+ goes. What is a maintenance hassle is computers in the battery talking to the charger or display. In 3 to 4 years when the cells in the bionx wear out, what are you going to do, buy a new bike? My battery is generic, has a 2 wire interface, + & -. No sourcing problem for 20 years, probably, I just have to build a mount for a new battery as I did this time for the one I'm using.
As far as the drag of a 60 lb aluminum frame vs a 30 lb carbon frame, you get a lot more drag out of an IGH like a rolloff. Those planetary gears in there roll around all the time, the selector just picks which one is engaged. Your feet or the motor power all those gears all the time. I tried an 8 speed Sturmey Archer S80, it slowed me down 20% versus the 21 speed derailleur I was using on the 70 lb MTB bike.
BTW my build was $2800 with accessory lights, 2 leg stand, panniers (bags), front basket (which I replaced with the battery mount). The cushy seat was $10 at salvation army with a throw away 27" tire bike attached.
 
Last edited:

drewberz

Active Member
The GMAC from ebikes.ca was a high speed winding. Thus low torque. I ride 72 hills on my weekly commute, I use a geared hub motor. The DD hub motor I had before (like the GMAC) used about 50% more electricity on all those hills. With 60 lb supplies & tools my outbound gross weight is 300 lb.
I don't understand the obsession with carbon frame for an ebike. You sound male, you weigh presumably 150 lb or more, the motor & battery weigh 16 lb or so. What is the problem with a 60 lb aluminum frame + drive? I lost 60 lb of lard with a 75 lb steel bike after I quit working. Most North American males could stand to do the same.
Carbon fork is definitely incompatible with front drive bafang geared hub sold by ebikes.ca, and it won't smooth out the bumps of going 28 mph either. 32 mm tires are also bump transmitters. Only people that live in Germany have pavement smooth enough to ride 28 mph on 32 mm tires without suspension IMHO. I use 2 " (56 mm) and it is rough enough to be annoying with no suspension at 10 mph. I do hit 30 mph peaks downhill, but only on good pavement hills.
With hub drive I'm already up to 5000 miles on my chain without maintenance or symptoms. What's wrong with 8 speed chain? Yeah, 11 speed chain is a hassle, 1000 miles per, according to road bike review. So why not put the extra speeds on the front sprocket? You can't do that with belt drive. I have 24 speeds with my 5000 smile endurance chain, 3 x 8 speeds.
As far as maintenance hassle of a bafang hub, you use them up and throw them away. You don't maintain them. $200-300 for a motor, what's the problem? I've got 3000 miles on my ebikeling geared hub motor, no symptoms yet, and the wiring was compatible with the 1000 W DD hub I got for $189. With customs charges going through the roof I've already stored the replacement hub motor + controller + brake handles in the garage. Unlike a battery, a hub motor won't age. The capacitors in the controller will, but I replaced those in the ebikeling motor a month after I installed it. The OEM ebikeling electrolytic capacitors were **** grade and sparked the battery connector every time I plugged it up. You can buy 10000 hour life @ 105 deg C capacitors at farnell or digikey, manufacturers love to limit the life of their product with **** capacitors so you'll buy a new device in 2 to 5 years.
The battery is where $700+ goes. What is a maintenance hassle is computers in the battery talking to the charger or display. In 3 to 4 years when the cells in the bionx wear out, what are you going to do, buy a new bike? My battery is generic, has a 2 wire interface, + & -. No sourcing problem for 20 years, probably, I just have to build a mount for a new battery as I did this time for the one I'm using.
As far as the drag of a 60 lb aluminum frame vs a 30 lb carbon frame, you get a lot more drag out of an IGH like a rolloff. Those planetary gears in there roll around all the time, the selector just picks which one is engaged. Your feet or the motor power all those gears all the time. I tried an 8 speed Sturmey Archer S80, it slowed me down 20% versus the 21 speed derailleur I was using on the 70 lb MTB bike.
BTW my build was $2800 with accessory lights, 2 leg stand, panniers (bags), front basket (which I replaced with the battery mount). The cushy seat was $10 at salvation army with a throw away 27" tire bike attached.
The torque figure was still high if I recall, 100nm?

I like carbon because it can be built to be light, but it's not necessary.

I am not what they call a 'weight weenie' by traditional bike standards, but handling a 60lb.+ bike on a train and up 3 flights of stairs multiple times a day gets tiring. I am 190lbs. and weigh 175lbs. when I was in top race shape.

I hate the idea of throw away and the maintenance you mentioned. I'd rather maintain something than anticipate tossing it in 2-3yrs.

I definitely want a serviceable battery too. Want to steer clear of bankrupt companies such as Bionx or proprietary casings.
 

Thomas Jaszewski

Well-Known Member
indianajo is a genius at scrounging and building. Incredibly helpful and inventive! BUT he hasn't the insight into the GMAC.

Use the calculator on ebikes.ca. It's quite accurate.
 

indianajo

Well-Known Member
RIDING a 75 lb bike is not a problem for a 175 lb male, especially with power assist. I'll concede CARRYING it 2 flights would be a problem.
One solution to carrying the bike upstairs is to not do it. Buy a $75 steel frame bike off craigslist/gumtree/bargainmart or a charity resale shop or flea market. One NOT WORTH STEALING. You can find drop handlebar road bikes, may cost a little more than the kiddie grade MTB & cruisers I have bought. Buy your hub motor of choice, install it with double nuts. Remove any "quik-change" skewers and replace with bolts and nuts. Same with the seat adjustment. Buy two 1/2" x 6' cables, serious locks, a bag to haul them, then cable your frame & power wheel to a power pole or gas pipe OUTSIDE. I like Stainless Steel cables, a real P*** to grind through. Sold as sling cables by industrial supplies. Design your battery mount for quick removal and take it with you upstairs. That is where the money is. If someone steals the bike & motor anyway, you're out $400 + a taxi ride & shopping experience. Not worth insuring. The money is in your gym bag at your desk, the battery.
I see elsewhere the Gmac is a mac geared hub motor modified to have regenerative braking. I prefer a standard MAC as I pedal myself a lot and use the one-way clutch 70% of the time to be free of drag. But people have different needs. A clutchless model may be just the thing for a dedicated commuter e-bike.
 
Last edited: