"True assist": is anyone else doing this?

[Samd]

+1 kepler. Thanks for articulating what I could not after a loooooong week.

 

[GCinDC]

...This is what I am calling "true assist," i.e., a system designed only to assist the rider, not to allow him to use his bike as something closer to a motorcycle. The aim of true assist, rather than being how fast the motor can propel the bike or how far the battery can take the motorized bike with no pedaling by the rider--which really aims at maximizing assist--is to determine what minimal amount of assist is going to be enough to ease the rider's exertion in difficult terrain.

i'm still having problems with your definition. what is "true assist" again?

sounds more like "minimal assist".

or just assist?

as·sist
/əˈsist/
Verb
Help (someone), typically by doing a share of the work.

what's cool about the bionx, once you set it up to do 300% of your power, you can pedal easy, and it goes easy, or you can pedal really hard, and it goes that much harder, esp on hills, up to it's governed speed limit, which is too slow IMO to make it interesting to most fast cyclists, but that's another issue..

i have no idea how other pedelec or torque sensing systems work, but i mainly just wanted to write to say the expression "true assist" bothers me, and is not at all descriptive. sounds purely subjective...

 

[MadRhino]

Pedal assist means just that. Helping power is commanded by pedal power and/or cadence reading. This implies no specific speed or power level. A 10Kw system could be a true pedal assist, if it was commanded only by crank sensing.
As soon as you are using a throttle it is not a pedal assist anymore, even if it is a lame 200w system.

 

[dogman dan]

That's part of why I was having problems understanding. Throttle control gives you any assist level you want, except perhaps less than 50w. What's not true assist about it if you aren't going faster than the bike is geared for. My racing bike went 47 mph, but out of the corners I had tall enough gearing to pedal hard and use pedal assist to get back up to speed faster, and stick the tire better. Different, but still assist.

I keep getting the idea that he wants "no think about it" assist except to turn it on and off. Pedal assist, + power level switches is pretty close to that.

It's definitely a pita to try to ride a system designed for 20-25 mph at 10 mph. 15-20 mph not so bad, but below 10 mph you lack throttle control. It goes to on- off 100w. You get this jerky, too much too little thing going on. I think that's what he's hating.


I don't have this problem at all with the slow motors. I can cruise at 5 mph all day on my 2812 motor, which runs on as much as 3000w btw. But because of the slow winding, I still have great throttle control at 5 mph.

I'll repeat this again, many times as it takes. Slow winding is NOT a lower gear like a smaller wheel is. Torque does not change with slower windings. Torque changes with wheel size though. He's got 20" wheel already anyway, and a 12t mac will give him a crazy slow top speed. And it will grind up big long 15% grades with no problem I think. He'd have great torque and great low speed throttle control, or pedelec would work better at the slow speeds.

 

[wayover13]

Thanks for the additional responses in this thread. I feel as though I'm learning more, although, lacking an understanding of some fundamental aspects of electronics, I can get easily confused by new information.

i'm still having problems with your definition. what is "true assist" again?

sounds more like "minimal assist".

or just assist?

as·sist
/əˈsist/
Verb
Help (someone), typically by doing a share of the work.

Yeah, I've used the phrase "minimal assist" in describing my aims as well. As I've mentioned elsewhere, what this means for me is that the motor is not doing anything most of the time--including not adding excess drag. Where assist is needed, which will be primarily on uphill grades, the motor provides assist--accounting for perhaps as much 50% of the force propelling the bike to the crest. Then the motor disengages again until the next uphill grade.

i have no idea how other pedelec or torque sensing systems work, but i mainly just wanted to write to say the expression "true assist" bothers me, and is not at all descriptive. sounds purely subjective...

Yeah, as I've admitted, there's certainly subjectivity involved. If you looked at the Tetz web page for which I provided a link, that can give some further orientation to the concept as I'm formulating it. The Hilltopper kit, at least so far as the catchy name they've chosen to market it with is concerned, also embodies a similar aim. I felt the need to try and enunciate this concept here since, as I mentioned, so much of the thrust of e-biking seems oriented toward high-performance kits that make a bicycle into something more like an electric motorcycle. Against such a backdrop, I wanted to make it clear that, for my own uses, the motor's role will be minimal--it being primarily used to keep me from driving myself too hard getting my bike (with wife and gear) to the tops of grades.

Hope this helps.

I keep getting the idea that he wants "no think about it" assist except to turn it on and off. Pedal assist, + power level switches is pretty close to that.

It's definitely a pita to try to ride a system designed for 20-25 mph at 10 mph. 15-20 mph not so bad, but below 10 mph you lack throttle control. It goes to on- off 100w. You get this jerky, too much too little thing going on. I think that's what he's hating.

Again, while, for my purposes, an on/off switch seems as though it could be an improvement to the ideal system as I envisioned it* because it would further simplify things, it's not really related to true or minimal assist as I'm trying to define it. In any case, it's nothing I intend to implement in this upgrade, so we can set it aside in this discussion.

* The ideal system I was envisioning was a mid-drive system that drives the crank arms and matches typical pedal cadence to most efficient motor RPM through gear reduction: under this scenario, a throttle is an overly-complex solution for motor engagement.

 

[wayover13]

im using what i consider a "true assist" setup on my trike.

im running an ezee geared hub motor on 12s lipo (50.4v fresh of the charger), with a CA V3 and Thun BB.

i can easily get less than 3wh per km on most solo rides, and even when loaded up touring, i can get 6wh/km.
more often than not, i get home having provided more watts than the electric system has. it's usually close to 50/50 human vs electric.
most often it's more l like 65/35 human / electrons.

for one example, i recently did a 186km weekend tour and used only 19.1ah to do the distance, and that was loaded up with 14% hills in the mountain passes.

i am about to leave (tomorrow morning actually) for a 1200km 19 day tour.

Great to see others are doing electric-assisted touring. This is our primary aim and is why I'm researching assist systems. I'd say our assist proportions should be something more like 80/20 human/electric--that because we intend to use the assist almost solely for help getting up grades. It should be disengaged most of the time outside those conditions. Maybe I'll upgrade to the Thun BB at some point in the future, but for the initial phases of my intended upgrade I'll be sticking with a throttle.

 

[Diamondback]

My aim on this tour is to aim for about a 50/50% human - electric.

So far I'm not too far off that figure.

I'm on day 2 now.
867.3 watt hours
927.1 human watt hours

159km so far.

Jason.

 

[wayover13]

I grew up in Wisconsin, but spent the last 39 years in Virginia. My wife and I rode our RANS Screamer tandem for a decade, in the mountains of Virginia. After several knee surgeries, and a knee replacement, she has decided to quit riding. If you have a tandem with a 20" front wheel, and only want to use assist for climbing, there is no point in getting a mid-drive. You are making this way too complicated.
...
Get the 12T, in a 20" wheel for an ~15 mph top speed on 52 volts. Get this pack.
...
With this setup you will never have a problem climbing the steepest, longest climbs. You will never be tempted to use it for anything other than climbing, and perhaps starting from a dead stop. With the built-in freewheel in this motor, on a tandem, you won't even know the motor and battery are there, until you use it.

The above is really good advice for OP's request. I have a very similar cycling background and age etc to the OP. Generally I am interested in making assisted bikes rather than electric motorbikes. I don't have a tandem but am planning a cargo bike so the question "how do I get my older-weaker self and 150 lbs of compost up the hill to my house without horking up a lung?" has been something I've thought a lot about.

Yeah, I've horked up a few of those in my day. I don't think I have many left to hork.

A similar but lower budget, somewhat quieter, alternative to the suggestion from Diamondback that is even slower because it uses lower voltage would be: a 36 or 48V Bafang BPM front motor in a 20" wheel, a 25 amp controller and a 20+Ah battery in the neighborhood of 30-ish volts. You want a no-load speed of around 12-13 mph.

Assuming 440 lbs gross weight, and 250 watts pedaling input total, this combination will climb a 12% grade at 5 mph and is most efficient on a 5% to 6% grade (very common highway slope) around 9 to 10 mph. By 12 or 13 mph the motor is doing nothing which is what you are asking for. For example, with this setup you can climb Rabbit Ears pass (which I still remember from my cross country, 7%, 3000 ft gain) at 8 mph. It would still be a hard climb, but practical, not torture. All these combinations work without overheating the motor according to the simulator.

Get the motor first and measure the speed with a known voltage and then order the battery with the right voltage to get the no load speed around 12-13 mph. A Ping would be a good fit for this as he can make custom sizes, eg 33 volts last I checked. Since it's a tandem you can afford the space and weight. But anything 20+ah around 30-ish volts will work. This application is not going to demand much from the battery as long as it is big enough to be useful.

I think the control issue in this case is pretty simple. Thumb throttle with auto-cruise control, or almost even just an on/off button. Given that you only want it when you have a hill to climb, that the power is limited by the low current, and that it won't go very fast anyway, you are almost always going to want most or all of it. I'm assuming you can accept climbing 7% at 9 mph at full throttle instead of 7 mph at part throttle or 3.5 mph on your own.

Try out the ebikes.ca simulator, it is great for this sort of design exploration. For your criteria I used a 30 V 20 Ah battery, the 25 A controller, 20" wheel and the Bafang BPM motor (this is the 36 V motor, the 48 would be slower yet, you can scale the battery voltage to see some of the effect)

Interesting comments. I've actually got two bikes, one of which is being upgraded and the other of which I will probably add an assist system to later--both recumbent tandems. Climbing at 9 mph suits our pace just fine, that being a few miles per hour faster than we climb without assist (we can drop down to 5-6 mph on tough grades). I'm going to make a conservative estimate that our output wattage will be 300 instead of 250: as I mentioned, I like a brisk aerobic workout and am usually finding I need to restrain myself from working too hard. My wife is a lot weaker than me, but she does pretty good at keeping up a moderate pace for long periods. For the record, the hub-motor wheel I'm replacing on the bike I'm upgrading is a 16" (front) wheel, not a 20" wheel.

When you mention measuring "speed with a known voltage and then order the battery with the right voltage to get the no load speed around 12-13 mph," I presume you mean maximum no-load speed? I.e., with the throttle wide open? The only way I could really measure speed doing this as a sort of bench project, as I assume you're suggesting, would be by using the CA, correct?

I have looked at and played with the simulator and I even decided at a certain point on a hub motor. Then I started going over the respective advantages/disadvantages of hub motors versus mid-drives and began to waver. The ease of hub motor kits is hard to argue against. But there are disadvantages, e.g., fixing flats on your hub-motor wheel can be a pain since it's wired to the bike; I know that from experience. That problem is obviated with the mid-drive kit. The mid-drive kit seems to provide greater flexibility as well since, on those rare occasions when it might be needed (think sudden, rapidly-approaching thunderstorm and the need to find shelter), it could help increase top speed. But installation on a non-standard bike such as mine can be a bear.

 

[Warren]

The Stokemonkey is the only mid-drive I would consider buying. It is quiet, and durable. You could mount it to run off a second chainring on the stoker's left crank.

 

[wayover13]

The Stokemonkey is the only mid-drive I would consider buying. It is quiet, and durable. You could mount it to run off a second chainring on the stoker's left crank.

The stokemonkey was recommended to me in another thread on these forums and does look interesting. But it appears to be out of stock: supposedly it was going to be available again in the spring, but not much of spring is left and it's still listed as out of stock. They are located in Canada though, and I think their spring starts somewhere in early July or so, doesn't it?

 

[-dg]

Climbing at 9 mph suits our pace just fine, that being a few miles per hour faster than we climb without assist (we can drop down to 5-6 mph on tough grades). I'm going to make a conservative estimate that our output wattage will be 300 instead of 250: as I mentioned, I like a brisk aerobic workout and am usually finding I need to restrain myself from working too hard. My wife is a lot weaker than me, but she does pretty good at keeping up a moderate pace for long periods. For the record, the hub-motor wheel I'm replacing on the bike I'm upgrading is a 16" (front) wheel, not a 20" wheel.
...
When you mention measuring "speed with a known voltage and then order the battery with the right voltage to get the no load speed around 12-13 mph," I presume you mean maximum no-load speed? I.e., with the throttle wide open? The only way I could really measure speed doing this as a sort of bench project, as I assume you're suggesting, would be by using the CA, correct?
...
But there are disadvantages, e.g., fixing flats on your hub-motor wheel can be a pain since it's wired to the bike; I know that from experience

Yes, no load speed is wide open throttle with the wheel off the ground. Real speed on flat ground will be about 80% of this more or less depending ... To measure it, assuming it's not in a wheel, put the motor in a fork or stand or something so you can run it and just use a bike computer calibrated to the size wheel you want and stick or tape a magnet to the hub. Run the motor and hold the computer pickup near the magnet, no-load speed will be on the bike computer.

The 16" wheel and 300 watts makes this even project easier and more elegant. No need for a big motor like the BPM. Get the Bafang SWXK5 or SWXK (same except for disk clearance) and run it with with the small 6fet controller and a 15 Ah (or more) 36 volt battery. I have this motor and controller on my wife's bike and it has no load speed of 27 mph in a 27" wheel at 48 volts and is quiet, smooth and reasonably strong. In a 16" wheel it would have no-load of 16 mph at 48 volts or 12 mph at 36 volts which is exactly what you want. And, with all the extra leverage it would climb a tree. The advantage of the big motor is that it can dissipate heat when you lug it, but with a 16" wheel and a controller limited to 14 amps you won't be lugging it.

The Greenbikekit version of the SWXK and SWXK5 comes with a "waterproof connector" near the motor so it is easy to disconnect the to remove the wheel. I've attached a photo of my wife's SWXK in a 700c wheel. The connector is the bulge in the middle of the cable. Just cut the zip ties, unplug the connector and remove the wheel. Keep a few extra zip ties to replace them. Or use string or velcro or tape or something. I recommend ordering the sensorless version if possible as it is very smooth and as long as you don't need full thottle from a dead stop it will be perfect.

This motor weighs just under 3 kg and will let me pedal up a 12 % grade for a few blocks and I'm out of condition and weigh 270 lbs these days. I don't think it would be happy doing that for a long time in the 700c wheel, but in a 16" wheel and with under 15 amps input it should be fine.

 

[wayover13]

The 16" wheel and 300 watts makes this even project easier and more elegant. No need for a big motor like the BPM. Get the Bafang SWXK5 or SWXK (same except for disk clearance) and run it with with the small 6fet controller and a 15 Ah (or more) 36 volt battery. I have this motor and controller on my wife's bike and it has no load speed of 27 mph in a 27" wheel at 48 volts and is quiet, smooth and reasonably strong. In a 16" wheel it would have no-load of 16 mph at 48 volts or 12 mph at 36 volts which is exactly what you want. And, with all the extra leverage it would climb a tree. The advantage of the big motor is that it can dissipate heat when you lug it, but with a 16" wheel and a controller limited to 14 amps you won't be lugging it.

Interesting proposition. So you would say the MAC 36 volt 500 watt 12T motor I was considering would be overkill, given the usage scenario I've described?

The Greenbikekit version of the SWXK and SWXK5 comes with a "waterproof connector" near the motor so it is easy to disconnect the to remove the wheel. I've attached a photo of my wife's SWXK in a 700c wheel. The connector is the bulge in the middle of the cable. Just cut the zip ties, unplug the connector and remove the wheel. Keep a few extra zip ties to replace them. Or use string or velcro or tape or something. I recommend ordering the sensorless version if possible as it is very smooth and as long as you don't need full thottle from a dead stop it will be perfect.

Yeah, that connector looks like it could negate one of the cons of using a hub motor. But it seems to be offered only with the SWXK5 and, while the SWXK5 is listed as being sensored, it's the SWXK they list as having the option of being either sensored or sensorless (not that I really understand what sensorless versus sensored means, mind you). So it looks like one can't have one's cake and eat it too with respect to these two motors, correct? Definitely no need for full throttle from a dead stop on this bike, no.

This motor weighs just under 3 kg and will let me pedal up a 12 % grade for a few blocks and I'm out of condition and weigh 270 lbs these days. I don't think it would be happy doing that for a long time in the 700c wheel, but in a 16" wheel and with under 15 amps input it should be fine.

Certainly would be great to lower the weight this kit adds to the bike. My current DD hub motor/wheel must weigh about 20 lbs. (it's in a cast aluminum wheel).

 

[Rassy]

I've just completed installing an old (actually almost new, but I've had it around 4 years) Bafang motor as a 16" BOB trailer pusher for his trike. This is the one that is wound for lower speed and meant to be used in a 26" wheel. If I remember right it tops out at about 14 MPH on 48V in the 16" wheel.

Anyway, it is a true "assist" since there isn't enough weight on the wheel to keep it from spinning out if you push it too hard.

We did a number of rides last week-end to put the trailer through its paces. Altogether we covered about 40 miles on all kinds of hills. One ride included a 1 mile steady climb of about a 10% grade, which we rode slowly on purpose at about 5 or 6 MPH with no heating issues. There were also several rides that ended up with the 20% grade on my driveway. He mastered the throttle right away and was able to use it for assist without spinning the trailer tire. Well, except for one steep little section of gravel where he spun out both his pedal power trike wheel and the pusher trailer wheel. I circled back and gave him a push with my trike, one advantage of having a lot of weight on my drive wheel.

Our watt meters are mounted with the batteries and not visible when riding, but each time we checked them he had used less than half the Watt hours I had used, even though I pedaled all the time also.

http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=49207

So everything you've said about wanting an assist on the hills makes me think a throttle operated, slow wind, geared hub motor would serve you the best. Simple, light weight, and ample power when needed in that 16" recumbent wheel.

Good luck with your next build.

 

[-dg]

Interesting proposition. So you would say the MAC 36 volt 500 watt 12T motor I was considering would be overkill, given the usage scenario I've described?
...
Yeah, that connector looks like it could negate one of the cons of using a hub motor. But it seems to be offered only with the SWXK5 and, while the SWXK5 is listed as being sensored, it's the SWXK they list as having the option of being either sensored or sensorless (not that I really understand what sensored versus sensored means, mind you). So it looks like one can't have one's cake and eat it too with respect to these two motors, correct?

Yes, the MAC would be total overkill. I recently tried another members bike with the MAC and it was a beast. Very impressive, but totally overkill for your situation. It is also louder than the Bafang motors I've heard so far. Not as bad as my mid-drive, but still objectionable at least to me.

Either the SWXK or the SWXK5 will work. And sensored or not does not matter, you can always just not wire the sensors up, the controller will work both ways. Or just use the sensors, there is no harm in it. It's just that the connector is a little more robust (fewer pins) on the unsensored motor so all else being equal I'd prefer it. Also, the SWXK5 requires building an offset wheel (like a rear wheel) which is a little less desirable. On the other hand it fits more forks and discs which is why I think it maybe replacing the SWXK. As far as I know they are the same internally.

Btw, I'm really pleased with the SWXK. I fitted it to my wife's bike in hopes that she might ride more if it was a little easier (we live in a hilly area). She was skeptical and concerned that it would ruin her bike as she hates my mid-drive which had put her off the whole idea of electrics. This project has been a complete success. Her bike still rides nicely without using the motor and the motor is unobtrusive in use and more capable than expected. No complaints. Best of all she has been taking rides that she has not been up to for over ten years and coming back tired but happy instead of exhausted and cranky. She even takes it to work (12 mi round trip, 800 ft climb on the way in) which would have been impossible otherwise.

 

[dogman dan]

Overkill is good when the hill is long enough and steep enough. That's why I recommended it. The extra time it will take to heat soak it will make all the difference on a longer hill.

Bear in mind, I tend to think in terms of worst case scenario because I ride them all the time. So I tend to recommend like the person will ride up 10 miles of 8-10% grade, AND, it will be 100F with a 20 mph headwind.

The smaller motor will do fine for lesser days, till it hits that headwind. Then it stalls the motor, and overheats. BUT, and this is a huge but, in a 16" wheel, it will take a hell of a lot of hill, and a lot of wind to stall even a smaller motor.

Nevertheless, I stick by the recommendation for a larger motor for one crucial reason. TWO people will ride that bike. It's a lot of weight to lug up steep hills. Stall that little motor, and you will overheat it very fast. Mo betta to get a motor that won't stall, because on that horrible day, you can just feed it more power. Most of the time though, you'll be fine with less than 250 watts.

On the other hand, a smaller gearmotor is very cheap. It won't cost you much to try it.

 

[-dg]

Overkill is good when the hill is long enough and steep enough. That's why I recommended it. The extra time it will take to heat soak it will make all the difference on a longer hill.

Bear in mind, I tend to think in terms of worst case scenario because I ride them all the time. So I tend to recommend like the person will ride up 10 miles of 8-10% grade, AND, it will be 100F with a 20 mph headwind.

The smaller motor will do fine for lesser days, till it hits that headwind. Then it stalls the motor, and overheats. BUT, and this is a huge but, in a 16" wheel, it will take a hell of a lot of hill, and a lot of wind to stall even a smaller motor.

Nevertheless, I stick by the recommendation for a larger motor for one crucial reason. TWO people will ride that bike. It's a lot of weight to lug up steep hills. Stall that little motor, and you will overheat it very fast. Mo betta to get a motor that won't stall, because on that horrible day, you can just feed it more power. Most of the time though, you'll be fine with less than 250 watts.

On the other hand, a smaller gearmotor is very cheap. It won't cost you much to try it.

I partly agree with the general sentiment but, I think they will be happier with the mid-sized motor:

- They are doing these rides now, either without assist, or with a motor that is entirely unsuited to the application.
- The OP has expressed a strong preference for "true assist" and desire to minimize involvement with the motor. I don't think a large motor meets the user experience goals for the OP.
- I believe that they can get away with using the mid-sized motor. Given a no-load speed of only 12 mph and a controller limit of 15 A and 300 watts of rider input they will be going too slowly to keep the bike upright before they bog that motor.

 

[-dg]

Overkill is good when the hill is long enough and steep enough. That's why I recommended it. The extra time it will take to heat soak it will make all the difference on a longer hill.

Bear in mind, I tend to think in terms of worst case scenario because I ride them all the time. So I tend to recommend like the person will ride up 10 miles of 8-10% grade, AND, it will be 100F with a 20 mph headwind.

The smaller motor will do fine for lesser days, till it hits that headwind. Then it stalls the motor, and overheats. BUT, and this is a huge but, in a 16" wheel, it will take a hell of a lot of hill, and a lot of wind to stall even a smaller motor.

Nevertheless, I stick by the recommendation for a larger motor for one crucial reason. TWO people will ride that bike. It's a lot of weight to lug up steep hills. Stall that little motor, and you will overheat it very fast. Mo betta to get a motor that won't stall, because on that horrible day, you can just feed it more power. Most of the time though, you'll be fine with less than 250 watts.

On the other hand, a smaller gearmotor is very cheap. It won't cost you much to try it.

I generally agree that overprovisioning is prudent which is why I started out suggesting the BPM. However, I still think they will be happier with the mid-sized motor:

- They are doing these rides now, either without assist, or with a motor that is entirely unsuited to the application. So the motor only has to help, not carry the whole burden.
- The OP has expressed a strong preference for "true assist" and desire to minimize involvement with the motor. I don't think a large motor meets the user experience goals for the OP.
- I believe that they can get away with using the mid-sized motor, and the simulator suggests that this will work. Given a no-load speed of only 12 mph and a controller limit of 15 A and 300 watts of rider input they will be going too slowly to keep the bike upright before they bog that motor.

 

[Warren]

If you really don't think you will ever want the extra help, go with a tiny geared motor. But that 16" wheel is still only 75% as low as my low gear with my mid-drive. I see 450 watts in low gear, on my CA, at 8 mph up a 17% grade with me putting in 200 watts.

You should be fine if you crawl up at 4 mph, like I do on an unassisted bike. But one of the beauties of assist is climbing faster. The extra evaporative cooling is amazing! The cooling effect goes up exponentially.

 

[wayover13]

Yes, no load speed is wide open throttle with the wheel off the ground. Real speed on flat ground will be about 80% of this more or less depending ... To measure it, assuming it's not in a wheel, put the motor in a fork or stand or something so you can run it and just use a bike computer calibrated to the size wheel you want and stick or tape a magnet to the hub. Run the motor and hold the computer pickup near the magnet, no-load speed will be on the bike computer.

And how, exactly, does one output the varying known voltages to the motor so as to test maximum no-load speed? Is there some device that can be purchased for a reasonable price that will do this? I now understand the cycling computer part of your proposal and do have one laying around that I could use for such a test.

 

[-dg]

And how, exactly, does one output the varying known voltages to the motor so as to test maximum no-load speed? Is there some device that can be purchased for a reasonable price that will do this? I now understand the cycling computer part of your proposal and do have one laying around that I could use for such a test.

I use my battery as the voltage source. Just measure it's voltage with a Watts Up, CA, or voltmeter or whatever. Given the voltage at the start of the test and the speed tested you can then calculate the speed at any voltage you want.

 

[chas58]

I partly agree with the general sentiment but, I think they will be happier with the mid-sized motor:

- They are doing these rides now, either without assist, or with a motor that is entirely unsuited to the application.
- The OP has expressed a strong preference for "true assist" and desire to minimize involvement with the motor. I don't think a large motor meets the user experience goals for the OP.
- I believe that they can get away with using the mid-sized motor. Given a no-load speed of only 12 mph and a controller limit of 15 A and 300 watts of rider input they will be going too slowly to keep the bike upright before they bog that motor.

+1

I tend to go with this. If the bike is going to be used mostly without the motor, a small 2.2kg Cute Q100 with a 14amp controller and a no-load speed of 12mph would be just right.

You could put together your own "hill topper" kit to the same specs for a lot less money if you wanted to. Just don't use a bottle battery - those things are rated at 1C, and will not give you what you need for hill climbing.

 

[wayover13]

I use my battery as the voltage source. Just measure it's voltage with a Watts Up, CA, or voltmeter or whatever. Given the voltage at the start of the test and the speed tested you can then calculate the speed at any voltage you want.

This has the potential to turn out as a sort of chicken/egg dilemma: you need a battery to test the motor to see what sort of battery you need to buy for the motor. But I do have the battery pack I got with my original DD hub motor and it should still have some life in it. It was originally rated at 10 Ah and 48 volts. I could probably use it for such a test and extrapolate from there.

 

[-dg]

I tend to go with this. If the bike is going to be used mostly without the motor, a small 2.2kg Cute Q100 with a 14amp controller and a no-load speed of 12mph would be just right.

I think the Q100 is going too far in this direction, the motor I'm suggesting is 3 kg, the BPM which would be my next choice is over 4 kg. I also don't like the Q100 stub axle construction for a tandem, I'm concerned it might not handle the weight.

 

[arkmundi]

I've looked at hub motors and thought seriously about ordering one: they're definitely the simplest solution and could serve my needs adequately.... What I've been hoping to find as I try to finalize my upgrade decision, is relevant hard data.

I did a lot of research before making my purchase decisions, ultimately choosing the Heizmann 500 watt hub motor and building an A123 AMP20 battery pack. Got the motor, controller & throttle through Heinzman US and sourced the cells through Victpower. http://www.heinzmannusa.com/components.html. victpowersales@victpower.cn

I believe the essential decision tree is to start with how fast and how much power do you need for your riding preferences. Then based on that, size and build or buy a battery to match the wattage. I'd encourage you to go with a geared hub motor like the Heinzmann as it provides more torque for the hills. All the data you need for your research project I believe can be found on this forum - just put in the time to do the research.

I can attest that the geared hub motor works great as an electric assist, with very little drag when the throttle is off and in pedal only mode. The hand-grip throttle I have, which came with the Heizmann kit, is very easy to use, so finding the correct amount of electric assist, which differs on flats as versus hills, is quite easy to maintain. I always pedal, except when coasting downhill and my. Best of luck!

 

[emiyata]

True assist... no such thing at this point in time and I don't think it will in the future. I think you may need to change your mind set. My prime example is the film camera type finder on digital cameras being replaced with the LCD screen on the digital camera. Most digital cameras now days evolved to use this type of finder and people don't even think of the old style finder. A majority of the people buying the camera finds it superior to older finder and works well with the technology. Here you are dealing with kits that give you a crude but effective electric bike. This is much like the first digital SLR camera kits, they worked well but to me they fell short in features compared to new cameras. I think to satisfy your needs you need a top down total redesign of the bike to give you the weight and friction levels you desire. I just don't think we have enough people that wish to put out the type of money to have a bike that meets this type of design. I think you get stuck in this bicycle mind set that don't really work well with this ebike technology and you may have to accept some changes on how you ride your bike. I had the idea of getting an expensive PAS sensor on the bike but decided not to do that because I still get the workout I want and haul as much cargo I need. All I do now is do it a bit differently then I did in the past. I never could be in good enough shape to haul 50 lbs of cargo for miles at 20 mph and I am doing it a bit differently but it don't bother me at all. May just another angle to look at it.