How many watts do I need?

[PeteCress]

• 5 mph
• 275# bike + rider
• 8% grade, 1.25 miles long
• Mid motor (probably Bafang) running through a Rohloff hub

I am a long-term bike rider who cannot ride diamond-frame any more.

One promising workaround is a recumbent trike.l, but the end of most of my rides is a 1.25 mile ascent of an 8-9 degree slope and I am 99% sure I would need electric assist.

So that begs the question: "How much assist?"

Is 1,000 watts a no-brainer if I am willing to accept the added weight and whatever other penalties high wattage brings?

Or would 500 or 750 (or even 350) be plenty?

[MadRhino]

If you only need assist, you don’t need high power, for the slow speed that you plan especially. And, with moderate power, your BB drive will be reliable.

[TDB]

• 5 mph
• 275# bike + rider
• 8% grade, 1.25 miles long
• Mid motor (probably Bafang) running through a Rohloff hub

About 240W combined human and motor power.

[sleepy_tired]

Is 1,000 watts a no-brainer if I am willing to accept the added weight and whatever other penalties high wattage brings?

750 watts is 1hp. That is enough to get 25-30mph on flat ground without pedaling. I like to have a 1-2hp bicycle conversions. which is 750-1500watts. It won't stop you from avoiding pedaling on steep hills.

1-2hp is the traditional 'moped' range you let 13 year olds drive around.

That is only 2-4kg over a 350 watt system. Still plenty light enough to pedal without any motor assist. But powerful enough that you don't have to pedal if you don't feel like it.

If you only have 250-500 watts then that means that you'll have to pedal on anything except perfectly flat ground. Once you get to 3kw you have left bicycle-land far behind.

How much works for you depends on your specific situation. 1kw is a good all-around bike.

[markz]

1kw @ 275#'s is the bare minimum, having the ability to grab more power if you want it is good to have.
Having a good motor that can handle the power, buying a sufficient yet good quality battery to handle that power, then limiting it all with a cheap controller.

BBSHD
48V 40A ##Ah Battery
48V 10-25A Controller - Cheap to upgrade if you want more power because your battery can handle it.
Lets say you grab a 48V 20A controller and you find that one hill you need just that bit extra amount of peak power then all you do is buy a $40 30A controller and your not stuck with wimpy power because you bought a 48V 20A battery.

[dogman dan]

In the lowest gear, the smallest bafang mid drive would be enough to climb the hill at 5 mph. So 350w. But the weight difference is so minimal, I'd suggest a 750w, 36v kit. You'll like going up the hill at 10 mph more.

[TDB]

Something to be said for low power and lightweight systems. Power and weight especially the battery spirals out of control fairly quickly.

[spinningmagnets]

A mid drive with only 5-mph will be geared very low. Smallest chainring and a large-diameter sprocket on the rear wheel.

A standard-issue BBS02 at 52V can easily do this. The rohloff is expensive. If the external gearing is correct for 5-mph, then a cheap 3-speed IGH will be fine (Nexus, Sturmey, etc).

52V at 20A is 1000W, but if you keep the bike in low gear and actually run 5-mph, you will be using much less than that on the hills.

[Triketech]

500 watts for a Mid Drive. You'll lose the front derailleur; I've managed to add one with a fat bike Der but it adds more offset.
At 500 watts you can run a cassette with 3 speed internal safely - or any 8 speed and Rohloff. Rohloff is good to about 750 watts.

Both TSDZ and BBS02 drives can be easily set to 500 watts. Lightest weight and easiest to install options; it helps to have cable building skills.

Rear wheel size is important; 20/26 looks a bit sexier but 20/20 is going to finish the climb first. Some pretty nice ones out there, I'm a huge fan of HPV. 20" rear wheel reduces drivetrain stresses by about 1/3 compared to 26".

I would avoid a Direct Drive (DD) hub on a trike for hill climbs. You're going slower up the hills (and faster down) on a recumbent (a separate subject) so unless you want to ride at full throttle up a hill the motor will be operating in a lower efficiency zone churning 30-50% of the power into heat at 8-10 MPH. On the flip side (literally ?) a DD does make a nice speed retarder but doesn't return as much regen as it loses in efficiency losses.

Balance the load. Most trikes like ICE, Catrike, Terratrike tend to lift the rear wheel on hard stops. Poorly balanced IMO. Its not hard to mount the battery below the seat for a Mid Drive. With a Hub Drive the battery should be mounted under the boom for balance. No one makes an underboom mount so it takes some creativity.

Geared hubs are great but complex. That's what I run although I have the the skills and equipment to build the system.

I've written a few articles on the motors I've tested on an HPV FS26. These were from 5 years ago, I've put over 5000 miles on it since. Trouble free. Recently upgraded the battery and mount (no images yet). Reduced weight and looks better than any of the current factory installations.

Bafang BBS02 with DualDrive
TSDZ2 with DualDrive
MAC 10T Geared Hub 3x10

[E-HP]

BBS02, 48V 8Ah battery, 36 tooth front chain ring looks like it would work. Not sure about the estimate of the rear sprocket relative to the IGH low gear, but you can play with that to replicate the ration the Rohloff's capabilities. Also, not sure what size wheels are on the recumbent.
https://ebikes.ca/tools/simulator.html? ... =125&tr=50

[Triketech]

Watts Up?

To determine watts requires velocity. I plugged in 10 MPH. This returns only the power in Watts consumed by gravity for the climb; not the rolling or aero friction. Speed is linear can double the Watts for 20 MPH. Of course aero drag not included which at 20 MPH would be in the 250-300 watt range.

Total Wt= 275
Speed MPH= 10
Speed FPS= 14.67
Hill Grade= 8%
Rise FPS= 1.17
Ft.-Lbs/Sec= 323
HP= 0.59
Watts= 438

And for extra credit given the climb is about 600 feet this tells you how many watts the force of gravity consumed total on the climb.

Climb Feet= 600
Time Seconds= 511
Time Hrs= 0.14
Watt-Hrs Net= 62
Eff= 70%
Watt-Hrs Gross= 89

It helps to have a spreadsheet with formulas.

[Triketech]

Here is a sweet trike for sale with TSDZ2 & Rohloff...



http://www.bentrideronline.com/messageb ... p?t=156158

[Chalo]

Here is a sweet trike for sale with TSDZ2 & Rohloff...

I guess they wanted it to average out at okay quality and reliability?

[MikeSSS]

There are watts calculated from climb speed and weight. There are watts needed to maintain that speed due to rolling friction and air drag. Then there are watts needed to overcome inefficiencies in the drive train, tires, wheel hubs, etc. Total watts include the preceding power requirements. Human watts reduce motor watts.

For 8% grade, 275 lb, I get total power watts of 219 just for moving the weight up the grade without rolling watts and inefficiency watts. If the rider provides 50 watts then motor watts are 169.

Then I applied a 1.5x multiplier to account for road speed power, aero drag power and inefficiency power. The result is 328 total watts, subtracting 50 watts human power, the motor power needed is 278 watts. For 10 mph I get 606 watts motor power. This is about the power I see on the Cycle Analyst V3 on my two wheel bike when climbing at 10 mph.

An internally geared hub probably has lower efficiency than chain over big cogs. Because the IG hub also has a cog but also has internal gears.

[TDB]

Pete

Gravity drag is tenth grade physics with E=m.g.h and E=P.t equations at the core. Don't need to pretend to be Einstein. If you don't know what it means it doesn't matter.

There are online calculators that handle the missing variables.

Grin motor and trip simulators (use manual plot) are examples that will solve also for aero and rolling drag, human and electric motor power. Kind estimates for a loaded trike and bloated driver are CdA about 0.6 and Crr about 0.006. Human effort of 100-150W for unconditioned rider. Go play.

250-500W is plenty for most purposes. More is just for fun.

[JackFlorey]

One promising workaround is a recumbent trike.l, but the end of most of my rides is a 1.25 mile ascent of an 8-9 degree slope and I am 99% sure I would need electric assist.

So that begs the question: "How much assist?"

Is 1,000 watts a no-brainer if I am willing to accept the added weight and whatever other penalties high wattage brings?

Or would 500 or 750 (or even 350) be plenty?

As other people have said, 250 watts would be plenty; with a mid drive you have the advantage of all that gearing, and with a trike you don't have a minimum speed you have to maintain.

Choose any mid drive that fits and is over 250W (i.e. almost all of them.) Also make sure you do the math with your drivetrain and ensure that the chainring speed you need is compatible with the motor.

[Triketech]

I guess they wanted it to average out at okay quality and reliability?

Not sure. The seller has a few nice trikes.

Over the last few months a couple of jewels have surfaced in the trike market, this is one of them.

[PeteCress]

500 watts for a Mid Drive.

After reading your MAC 10 cookbook, I was all fired up on a MAC installation - primarily for the minimal noise.

But "The devil is in the details" and the more I read, the less confident I became in being able to procure all the components and get them working together.

Right now, I am thinking "750-watt BBS02, live with cadence-only, and hope the noise isn't too bad."

The ideal would be an "Ultra" with nylon gears dialed back to 500 watts (ISIS-standard cranks + minimum noise compared to steel gears), but that's not going to happen within my time frame.

I have settled on an HPV FS Scorpion with the high (22") seat and you have me thinking maybe the 20" model.

I have a 7-day Outrider demo arriving next week for general 'bent proof-of-concept, and then we will see how 20" wheels cope with climbing curbs....

http://www.triketech.com/index.html is a fascinating and informative read. Thanks for all that work.

[TDB]

Here's a question for PeteCress.

Do you really need to have five threads running for your build questions?

[PeteCress]

Do you really need to have five threads running for your build questions?

I figure granularity is good.

To wit:

• Different threads for different questions makes the resulting data more useful to others in later times by making it more easily searchable by subject line.
• Different threads for different questions increases my own chances for hits as people see a question that interests them enough to respond to.

Reducing to the ridiculous: "What is the sum and total of human knowledge" might be a good single thread in some respect or another, but the subject line is not going to tell people anything useful - either those searching for answers a year from now or somebody who might want to answer a specific question.

YMMV, and maybe I'm dead wrong, but that's my thinking on it and I apoligize if I'm being a pain in the ass.

[PeteCress]

Over the last few months a couple of jewels have surfaced in the trike market...

Besides CraigsList, where do you look and what do you search on?

[donn]

With a Hub Drive the battery should be mounted under the boom for balance. No one makes an underboom mount so it takes some creativity.

It looks to me like t-cycle.com has a couple variations on battery mounts that can go under the boom. Worth a look if you haven't been there.

[TDB]

Do you really need to have five threads running for your build questions?

I figure granularity is good.

To wit:

• Different threads for different questions makes the resulting data more useful to others in later times by making it more easily searchable by subject line.
• Different threads for different questions increases my own chances for hits as people see a question that interests them enough to respond to.

Reducing to the ridiculous: "What is the sum and total of human knowledge" might be a good single thread in some respect or another, but the subject line is not going to tell people anything useful - either those searching for answers a year from now or somebody who might want to answer a specific question.

YMMV, and maybe I'm dead wrong, but that's my thinking on it and I apoligize if I'm being a pain in the ass.

It's gets to the point where it is just noise... Here we go again!

How about doing some reading and research.

Good luck.

[E-HP]

I figure granularity is good.

To wit:

• Different threads for different questions makes the resulting data more useful to others in later times by making it more easily searchable by subject line.
• Different threads for different questions increases my own chances for hits as people see a question that interests them enough to respond to.

Reducing to the ridiculous: "What is the sum and total of human knowledge" might be a good single thread in some respect or another, but the subject line is not going to tell people anything useful - either those searching for answers a year from now or somebody who might want to answer a specific question.

YMMV, and maybe I'm dead wrong, but that's my thinking on it and I apoligize if I'm being a pain in the ass.

Don't know why you feel the need to apologize. The irritating posts are the ones where they copy and paste the same exact question in 4 different sub-forums, then bump them every 15 minutes.

I read your posts; I don't have much to contribute, but they are all distinct questions, with background about the questions included, and posted in the appropriate sub-forums (although arguably the sound comparison one may have been posted in Non-Hub Motors).

Besides, 271 posts in 12 years? I'd say you're not exactly abusing the system.

I see an uptick in trikes/recumbents around my area lately. I saw a guy with a BBS02 today (judging by the size) on his recumbent, and it wasn't really audible above the sound of my knobby tires when he rode by.

[Chalo]

I saw a guy with a BBS02 today (judging by the size) on his recumbent, and it wasn't really audible above the sound of my knobby tires when he rode by.

The BBS02 I had was quieter than either of the direct drive hub motors I use now.