Taking the edge off: smaller assist and longer battery life?

[Lowell]

The original poster wrote: "I might be lucky in that Canberra is relatively flat with heaps of bike paths."

 

[Dunhill_BKK]

Well, I did say I just wanted to take the edge off, and that I live in a flat area with almost no hills. I also indicated later on that I was interested in LiFePO batteries. However, I don't want to get into specifics about a build for my situation.

I'm just curious about people building bikes for an assist, as opposed to no-pedal rides.

So far I've gotten some interesting responses, the tooth count response being the most interesting to me so far. It's something I'd not considered at all.

So, I don't reckon the purpose of my post is to get specific, as you request, but to let the discussion broaden about systems built purely for assist and prolonging battery life.

 

[eP]

Well, I did say I just wanted to take the edge off, and that I live in a flat area with almost no hills. I also indicated later on that I was interested in LiFePO batteries. However, I don't want to get into specifics about a build for my situation.

So far I've gotten some interesting responses, the tooth count response being the most interesting to me so far. It's something I'd not considered at all.

So, I don't reckon the purpose of my post is to get specific, as you request, but to let the discussion broaden about systems built purely for assist and prolonging battery life.

Universal systems purely for assist don't exist i'm afraid. The same way as universal bikes or universal rim size don't exist.

Each system has own specific positives and negatives for the sake of specific purpose.

We can dispute quite different purposes and each time we could advice quite different solutions for them.
For example novice biker need quite different asistance then advanced one.
So the system purely designed for novice and optimized for the sake of low cost/price would be to weak for advanced bikers needs.
And opposit example: system designed for advanced biker will be oversized and too costly for novice.

I can add from my personal experience: i was totally novice one and half year ago but last year i've done over 2000 miles without any assistance just for pleasure from "pain" (from hard trening).
I'm still interested in asistance systems especially designed for novice - how they could be done cost efficient( not for the sake of my needs - i can bike in partially hilly area without them - but for the idea only).

 

[JennyB]

Well, I did say I just wanted to take the edge off, and that I live in a flat area with almost no hills. I also indicated later on that I was interested in LiFePO batteries. However, I don't want to get into specifics about a build for my situation.

I'm just curious about people building bikes for an assist, as opposed to no-pedal rides.

So far I've gotten some interesting responses, the tooth count response being the most interesting to me so far. It's something I'd not considered at all.

So, I don't reckon the purpose of my post is to get specific, as you request, but to let the discussion broaden about systems built purely for assist and prolonging battery life.

Another thing to bear in mind is that once you go over about 12 mph most of the resistance comes from the air, and that increases sharply the faster you go. Say you output 100 watts, and on a dead flat you can cycle 13.3 miles. Up a 10% grade you could only travel 2.5 miles in the same time.

Add 400 watts of assist and you will get up the same hill in just over 13 minutes, but 13.3 miles on the flat would take 31.5 minutes. That's assuming the ebike is as aero as a hybrid. If it were as slippery as a time-trial bike the time would drop to 25 minutes, or, more importantly, to maintain the same 25 mph speed would need only 170 watts of assist.

I'm an experienced cyclist and I like to take touring rides of 40-60 miles a day. If e-assist is to effectively extend that, then I need a set-up optimised for climbing and with minimal effect on unassisted performance.

 

[Dunhill_BKK]

I think I'd consider wind resistance as a constant in this case. Consider that when I hit the point where wind resistance starts to be the biggest limiting factor I'm happily cruising along and don't wish to go any quicker?

 

[Freddyflatfoot]

Dunhill, I reckon you should do yourself a favour and have a look at the elation kits (Australian). Low power. LiFeP0, and driven through the crank to maximise the limited power output.
I have a 250 watt system driving through the crank, and it does provide quite a bit of flexibilty.
By gearing the system right, you can still get good assistance at higher speeds, combined with pedalling, as well as good assist on the occasional hill.

 

[Dunhill_BKK]

As an Aussie I"m aware of the Elation kits, but I didn't know they had LiFEPO packs.

What do you think the difference would be between the elation-type system running through the gears and a geared hub? I reckon that one of the geared hubs, mentioned earlier in the thread might be comparable?

 

[Freddyflatfoot]

As an Aussie I"m aware of the Elation kits, but I didn't know they had LiFEPO packs.

What do you think the difference would be between the elation-type system running through the gears and a geared hub? I reckon that one of the geared hubs, mentioned earlier in the thread might be comparable?

They are both different, so depends on what you are looking for.
The geared system gives you heaps of flexibility, for climbing hills, low speed running, or windy conditions, without loading the battery.
You can also gear the system to match your own cadence, or for a personal preference, like gearing high for higher speeds, or gearing lower, to give you assist at lower cadences, at the expense of no/little assist at higher speeds/cadences.
For instance, I had mine geared down to a max cadence of 100 rpm, and used as little continuous power as 3.9 w/km.
Doing this would give you an extended range, at the expense of speed.

My trike, on the other hand, uses a small geared hub motor, that at 36v, gives me an unloaded speed of 55 kph.(It is geared for a 20" wheel, and it is mounted in a 26" wheel) Practical speeds are around 35 kph, and sometimes up to 45 kph, depending on wind and terrain. With pedaling, I have seen over 50 kph.
Haven't drained my battery to cut-off, but it is only a small 10 Ahr SLA pack, and have done better than 20k's. Also haven't connected my 'Watts Up' meter, so don't have ant empirical data on motor current draw or whr usage.

The hub motor would be better from a maintenance standpoint, and maybe more suitable for you in a relatively flat terrain. The geared hub definitely gives you more flexibility over a gearless hub motor, and as I have found, quite adequate performance. (My trike weighs in at over 40 Kg!)
With a 10AHr LiFePo4 battery pack, I would expect a 40k+ range, and a weight reduction of about 8-9 Kg!

My MTB with 24v/10AHr LiFePo4 pack weighs around 22 Kg, and has a range well in excess of 40k.

Mind you, I do tend to use my packs hard, so a more conservative use of power by moderating the speed somewhat, should see a comparable increase in range.

As for power output, notwithstanding the legal aspect, I would tend to look at a small geared hub motor at 36v for good performance.
To stay relatively legal, you would be looking at a 250w/24v system. Well 200 watt is legal, but we could see an increase in that to 300 w, but from a law enforcement point of view, is really splitting hairs. Probably never become an issue.

If you go for a hub motor, you will then have the choice of front or rear. Front is simpler, but will require a good solid, steel preferably, fork.
Rear motors tend to be limited with gear choices. My hub motor can take a 7 speed screw on cluster, and that's about it. Some motors take even smaller gear clusters. So depending on you current gear system, that would be another consideration.

Have fun working out which way you will go, and above all else, I know that you will enjoy the ebike experience! It's a great way to get around and commute.
Keep us posted on you get on.
Cheers!

 

[Dunhill_BKK]

Thanks for such an informative post.

I am also thinking about a recumbent as well, but possibly as an alternative to e-powered assist. However, it would probably be a great addition to add a relatively small hub motor to a 'bent. You already gain so much from being bent in terms of less drag and adding a small motor might see great improvements. I don't need to be doing 50 kph. Just getting to work without being drenched in sweat and get home without a numb butt is all I'm asking for.

I had thought that the hub motor could be better from a maintenance point of view.

Do you know of anyone who has powered more than one wheel of a trike? that might be very interesting.

 

[Freddyflatfoot]

Thanks for such an informative post.

I am also thinking about a recumbent as well, but possibly as an alternative to e-powered assist. However, it would probably be a great addition to add a relatively small hub motor to a 'bent. You already gain so much from being bent in terms of less drag and adding a small motor might see great improvements. I don't need to be doing 50 kph. Just getting to work without being drenched in sweat and get home without a numb butt is all I'm asking for.

I had thought that the hub motor could be better from a maintenance point of view.

Do you know of anyone who has powered more than one wheel of a trike? that might be very interesting.

If you don't want a numb butt, recumbent is definitely the way to go. And the view is sooo much better! Take a look at the Flying Furniture bike shop. He has some great bikes and trikes!
Dunno if anyone has powered more than one wheel on a trike, could be an issue when turning though! From a practical view, much better to power only the rear and KISS.
If you want the ebike for commuting, what is your commuting range? if you are on flat ground, just about any ebike would do the job. The question would then be, how fast do you want to go, or have the capability of going? A good capable ebike should be able to do 30 - 35 kph, and have a 25 - 30 k range.
And how heavy do you want it? Some of those Chinese imports can be heavy suckers!
Evehicle in Victoria has a good range of ebikes and kits, so you could check out their site as well. Or if you a backyard tinkerer like me, then have a look at Brett's site, google SolarBBQ.

Oh, I commute about 7 k's each way, and it is great to be able to get to work in good time, regardless of what the wind is doing, and with little effort, and little or no sweat! Well some sweat on hot days, but guess you gotta expect that anyway!

 

[Dunhill_BKK]

I've actually been to Ian's place at Flying furniture. I just didn't have the approval of the finance minister for the purchase. I've also talked with Brett a bit about motors and batteries.''My commute could be as short as 14 each way, or as long as 18 each way. It depends on how much traffic I want to endure, and that answer to that is as little as possible. Therefore, I'm looking to do about 18 each way, and do it at a comfortable 25 kph.

I think you are right about powering only the rear wheel on a trike keep it simple. I think a Grasshopper would be a good frame to try some e-assist. Nice small wheel, good German design and good quality control on the frame welds.

I'll have a look at Evehicle Victoria, I'm not sure if I've come across them before.

Cheers

 

[Dr. Shock]

I have a chinese knock-off of a Raleigh DL-1 (see photo) with a 350 watt brushed hub motor running 36v. In the rear, I have an SRAM s7 seven gear hub on a 16 tooth sprocket. It is my "exercise" bike. The SRAM gears with the 16 tooth cog is a great combination with the small motor. In low gear, it starts easily, and in high gear it lets me pedal as hard as I can with the motor going full bore. I enjoy the biking experience on this bike more than on either my unpowered bike or my higher powered (600 watt) cruiser, though the cruiser has the EV grin factor.

I haven't run a diagnostic to see what my battery use is, but the limiting factor on the range is my legs, not the battery.