Newbie - How does this look?

Hi, my second post, and thanks very much to all who have posted here - I've learned a great deal over the past couple of weeks reading all the old posts. I'm hoping that my research is OK and that the direction I've now opted to go seems sound.

I have a recumbent (a SWB TW Bent USS) that I would really like to use for my short (2 miles each way) commute to work. Unfortunately I pulled a thigh muscle badly (whilst paramotoring.......) and now find that sustained hill climbing is a real problem on the bent (any bent rider will know how hard hills are on the quads). My commute includes a long, (but quite gentle) grade on the way in that is enough to slow me down to below a safe speed in traffic. The fact that I am in my mid-fifties and not as fit as I'd like also has a bearing on my poor performance! Some power assist on the hill is my main aim, not all-electric power, as my intention is to use the commute to get fit as well as avoid doing short journeys in my Prius hybrid.

My chosen solution is a X'lyte 405 in the 20" front wheel, mated to a 35A controller. I already have a small stock of 12V 4.5A/Hr SLAs (with a 60A max discharge rate), so the initial plan is to use 4 of these as a test bed.

As far as control goes, I'd like to go pedelec, but hill starts on a bent are always challenging, so the option for a power start would be useful. I've ordered a thumb throttle, but plan to build a combined pedelec/throttle system. This should be easy enough, as it looks like the X'lyte controller just needs a 0 - 5V (or thereabouts) power control signal. If I put a cadence sensor on the bike and build a unit to mix the throttle and cadence outputs, such that the throttle can override the cadence sensor if required, then I think I should have what I want. I have a background in instrumentation design so this seems easy enough to do.

I've looked at bike power requirements and reckon that I need an average electrical input of about 200W for my commute, perhaps more on the way in but less on the way home. I believe that I will need about 80 to 90 W/Hrs of usable battery capacity for the two way journey. My 48V, 4.5A/Hr pack would give me a theoretical 216 W/Hrs, but I'm guessing that it's not sensible to use more than about 60% to 70% of theoretical capacity on SLAs. If my estimates are reasonable (any views?) then my SLAs might be OK as a permanent solution, although I might be inclined to invest in some lighter NiMH, or even perhaps Li Ion, batteries if it all works OK.

I'd appreciate any feedback on my proposed build - feel free to tell me I've got it all wrong!.

Jeremy

Sounds like you should be fine other than perhaps the batteries. SLA batteries will only supply about half their rated capacity at typical bike discharge rates. Don't be surprised if they discharge a bit faster than predicted. Nothing some used drill batteries won't fix. Since your commute is short, it might not be an issue.

Post some pics when you get a chance.

I agree with Fechter... better batts.

You may find the slope requires about 500w avg. draw, even if you're pedalling. Carrying the lead will just make it worse: it might be ok to test the bike w/ lead, but newer chemistries are the ticket to having a system that helps you; not you helping the system.

lead is dead, grab a small lifepo4 pack from somewhere. I'd probably suggest building a dewalt setup. 20 a123 cells might be sufficient to get you to / from work - (two 36v dewalt battery packs) at 2.3ah each in parallel that would give you 4.6ah - lifepo4 gives close to the rated capacity in high drain situations.

two dewalt packs dont' weigh very much either! The initial cost is much higher than lead, but once you've tried it you won't go back! i know i won't.

how fast to you plan to go?

The 405 is geared rather tall-- even with a 20" wheel. With that big 35 amp controller and i'm assuming 48volts, it's going to be very easy to completely discharge those batteries.

It's also going to be rather difficult to use this system in a peddal assist mode because you're probably going to want the motor to do all the work. The other slight problem with xlyte is the drag by the motor. It's not big but it's also going to make you want to use the motor all the time.

for freewheeling, a bmc from texaselectricbikes.com would be better. It's also almost half the weight!

I'm also of the general opinion that 35amps is way more than is needed for most ebike applications. the amps doesn't have a big impact on top speed but acceleration. *edit* we need to know how fast you want to go, but more than likely a 20 amp controller will fit your needs just fine.

Johndoh is right - check out the simulator at ebikes.ca - you should be able to see the comparison between motors easier. also if you look at the ebikes shop they have kph per V listed on the hubmotors page - this is useful for determining what your top speed will be at a given voltage with wheel combination.

choose carefully!

Btw the puma is a fantastic little motor!

Keeping in mind, acceleration is the same as slope... the OP indicated an interest in assist on hills.

35A is about right, IMO... but if the 405 is too tall, a puma would be a good choice.

Thanks for all the tips, I already have doubts about the SLAs, but they have the overwhelming advantage as a test pack of being free..............

I opted for a 405 and 35A controller after running loads of different options through the simulator at ebikes.ca What surprised me was that the low end torque curves for the 404, 405 and 406 were virtually the same for all three motors at low speeds. I opted for the 405 as it gave a good speed potential with the 20" wheel; speed on the flat is useful as the 'bent is inherently fast anyway.

None of the hills I have to tackle locally are particularly steep, it's the long gentle ones that I find a bit tough at the moment.

I'm looking at building the battery/controller box as a lost foam epoxy/glass moulding that will fit the odd space under the seat, between the main frame tube and the rear uprights. This will leave the rack free, which will be handy. It'll also mean very short cable runs and should look neat as well.

I'll post details of progress as things go - I should make the box this weekend, I'll just try and get as much volume as I reasonably can in the available location to leave room for future battery experiments.

Thanks again,

Jeremy