Tandem Trike Conversion

[Xray]

I am looking to convert our recumbent tandem trike to an e-trike. It is a hefty brute and it is hard for us to average more than 10 which makes it hard to ride with others. It is currently an 8 speed with a triple in front. I would like to be able to be able to cruise with friends on normal bikes or tandems so looking at 15-20 mph. I am hoping for assisted range in the 35-45 mile ball park. The trike has a 20" rear wheel with drum brakes all around. Combined weight of the 2 of us plus the trike is around 400 pounds. I am not looking to climb mountains with it but I do want to be able to do tours that include some hills like in southern Indiana. Dependability is a big factor for us. We have done 30 miles with the trike on flat rail trails before at a slow and steady pace.

Has anyone converted a tandem? I have been considering either a BBS02 500/750 watt version or a geared rear hub like the Mac 10. Which would be our best option for the kind of load we are dealing with? Is a 52 volt battery the best choice? How many Ah should I be considering? I see some sub $500 units on Luna Cycles in the 13 Ah range but I don't know if that will give us enough range. I am leaning towards the BBS02 right now. If I do go with the BBS02, how small should I go on the chainring? My first thought is to keep it small like a 34 or 36 (with an adapter) I typically shift quite a bit and keep a decently high cadence. The ideal would be to keep at least a double chain ring on, if that is even a possibility with the Bafang. Our budget is in the $1000-$1100 range for a complete system. I have built many bikes from frames and have no problems with the bike side of the build. I am the handyman type and do most of my own home and car repairs. Thanks for any help you can offer!

 

[Xray]

Here is the trike I want to convert: http://i217.photobucket.com/albums/cc259/BKXray/Troika_zpsnejxounw.jpg

 

[dogman dan]

This gets a bit tricky. But a mid drive would eliminate one problem, how to deal with brakes since your rear brake is a drum.

I'm too inexperienced with mid drives to suggest how to put one on that bike. But in a 20" wheel, a direct drive motor in the rear would be a good choice, if you have some way to make it use a rim or disc brake. I would hesitate to go with a geared motor because of the weight of two riders. But if the rides really don't go up steep hills, then a geared would work fine. Rail grades no problem.

Range is tricky, it depends on how fast you go, and I can't say from experience how the extra rider affects it. Dead weight I could, but not weight that also pedals. But lets do a calculation based on some guesstimates.

One rider, in general, puts out no more than 100w. This is a fit person, but not a trained athlete. So figure 200w for both of you max. 20 mph takes about 600w, for a 450 pound load. This I do know from touring. about 200 more than normal. So figure at least 400w or so including pedaling moderately hard.

400w for one hour, you need a 48v 10 ah battery. For a much longer ride, a 20 ah would be a good starting point for your battery. You may use more if windy, and will use less if you only cruise 18 mph instead of 20.

 

[Wheazel]

That looks to be a very comfortable tandem!
Personally I would go with a nongeared hubmotor and fix a discbrake solution for the rear wheel.
This would make a quiet drive, which I value extra high on a tandem where you can talk to each other.
The motor change I went through with my cargobike was for the better, and loaded with lotsa stuff that bike is approaching your weight territory.
You can see the details in my signature if intrested.

So for the relative low speed needs and the small wheel of the trike, a leafmotor would probably work well.
It wont be a hillclimbing monster, but should be well enough for what you ask with the approperiate wind.
I imagine fixing the discbrake would be a nonissue for a handyman.

 

[Eskimo]

Yep, a big DD and 20Ah or bigger 48V battery. Silent, bulletproof, powerful on flats. That thing puts a serious load on a rearwheel so you may need better spokes that motors have as a standard. At least some geared motors have certain axel load limits that might be exceeded on that. with 20Ah battery you will do 60-70km if you both pedal comfortably.
1000W DD kit is very affordable and powerful. Personally i might consider 1500W DD, so that it will do hills nicely and be sporty enough to ride with single sportriders.

 

[tomjasz]

BBSHD and 20Ah battery, but I just blew the budget. $1200-$1300 with a 20Ah battery. No mousing around with refitting new rear brakes. Those retrofits can get spendy too.
Every build has niggling details to sort. But that's the fun and the freedom that comes from understanding how your ride is put together. The later is priceless!



disclaimer I sell mid drives

 

[WoodlandHills]

Since all you want to do is keep up with other bicycles a BBS02 will be enough power. If you wanted to keep up with other eBikes I would say BBSHD. Either way it's the easiest and fastest way to motorise your trike. You will be able to retain everything from your current setup except the crank with its three chainwheels and your brake levers.

 

[Xray]

My concern with a DD hub is the drag when not in use. I plan on riding without the assist at times. Won't a DD hub make our trike even slower when not using power?

 

[WoodlandHills]

I would be surprised if you did much pedal-only riding after a few weeks of power assist..... As they say: power corrupts!

 

[craneplaneguy]

I'm glad to hear its not just me that loves the throttle! I've been feeling guilty.

 

[Chalo]

I am looking to convert our recumbent tandem trike to an e-trike. It is a hefty brute and it is hard for us to average more than 10 which makes it hard to ride with others.

But but but... recumbents are faster than normal bikes! Just ask anyone who has a recumbent! They have an unbeatable advantage. That's what you mean, right? That you can't ride with others because you effortlessly glide away from them at 10m/s, right?

OK, back on earth: My concern with converting your tandem is that hub motors make weak, trouble-prone wheels compared to normal hubs. And trikes are harder on wheels than bikes are because they apply side loads.

You'd be best served by a hub with relatively widely spaced flanges. And you should use the beefiest double walled rim you can find. An Alex Supra-E would be ideal, or maybe one of those Emoto rims that were surplussed out by Neal Saiki a few years ago.

Don't go nuts with heavy gauge spokes, because they need to be resilient to carry heavy loads. Heavy rims plus thin spokes make the strongest and most reliable wheels. I'd use 14-15ga double butted, with 2mm or #2 washers under the spoke heads.

It would be a good idea to use a hub motor whose wires exit from the thick inner part of the axle rather than the end. Hollow axle ends are a point of weakness.

 

[Chalo]

BBSHD and 20Ah battery, but I just blew the budget. $1200-$1300 with a 20Ah battery. No mousing around with refitting new rear brakes. Those retrofits can get spendy too.

There's also the issue that the chain drive is already coping with two riders' input, and a crank drive would add a whole lot more on top. It's not insurmountable, but it's something to consider.

I wonder whether this trike has furniture for rim brakes.

 

[Thud]

Do any of the BBSO recomenders notice we are dealing with a left side output on the foward set of cranks?
Doubt the rear set has the room, or the bbso will function in that senario.
Please educate us on this feature...


A proper fitting mid drive solves braking issues & potentialy lousy wheel life with a radial laced 20" wheel.

Xray-What kind of top speed are you seeking?


Off topic:
(Chalo is right....we need a upright tandom trike to make it viable ) Jebus man, ease up on general questions....no one asked for input on trikes, this paticular trike or recumbents in general. Comes accross as quite condecending...I suspect you could have worded your distain more ellequently, & provided unsolicited guidance beyond the scope of the op's question without the obvious sarcasim.

 

[Xray]

I do have a V brake on the rear as well as a drum. My current rear wheel is a monster with 44 spokes and a strong rim. There is hardly room to get an air pump on the stem the spokes are so close it is hard to get an air pump on. It also uses a 145mm tandem width hub.

There are fast recumbents of course but there are also slow recumbents. My recumbent bike is no slouch and I am comfortable riding with road bikes on it as long as the road bikes are ridden by my equally old friends. I ride recumbent for comfort though, not speed.

 

[Xray]

I have thought about using the BBS02 on the front boom and rerouting the chain to the right side. I think I would prefer to have it where the stokers crank is. That would keep the weight more centered and allow my wife to be able to stop pedaling if we want to go on motor power only. Here is a pic from the left side of the stoker crank. Does it look like there is enough room for a mid drive? http://i217.photobucket.com/albums/cc259/BKXray/stoker%20crank_zpsg3zrnu1v.jpg

 

[Wheazel]

Since you want to ride the bike without assist sometimes, did you consider a small push trailer with a silent dd hubmotor? Everything left on the bike when going without assist would just be some display and the throttle. Also very easy to build. Adds minimal weight to the actual bike.

 

[Xray]

Wheazel- we actually have a RideKick trailer that was bought for my daughter who has some disabilities. It was the catalyst for us to start thinking electric assist for our tandem. My complaints with it were that it was heavy (about 40 pounds with battery), rattled and banged a lot on rough roads, but mainly it couldn't handle the heavy tandem and would heat up too much.

 

[amberwolf]

First:

You might consider a *left side* chaindrive, where the motor (perhaps a hubmotor mounted in the frame rather than in a wheel, so you don't compromise your wheel strength *or* have to give up your rear drum) drives a chain to a sprocket mounted on the *left* side of your rear wheel. Assuming your drum brake hub will allow that sort of thing easily; if it doesn't, you could still do it by mounting to the spoke flange with an adapter ring.


If not, well:

Something to consider about thru-the-gears type of middrive, is that if you are using it with a freewheeling crank at the stoker, it's crank freewheel is going to have to handle the input from two people pushing a heavy trike, and it's not unknown for that freewheel to fail with just one person's input on a light bike. It's probably only a concern if you are riding without assist, or if you are heavily cranking on startup with minimal help from the motor, etc.


As for power levels...I ride a trike (SB Cruiser in my signature) that when carrying Tiny is probably more weight than yours with y'all on it, and it's only between 700-1000w to keep it at 20MPH, depending on wind/slope/etc, riding on "flat" roads. I don't pedal, cuz of my knees and stuff, these days, so iit's not geared for that, only for a single speed of really really slow so if I *have* to, I can still pedal it a little ways at a time without power. (only once, so far, hope to never repeat the process, and need to gear it down even lower).

I use a lot more power (3500w-ish) to accelerate very quickly to that speed, in a short few seconds, to get out of the way of traffic.

If you don't have to accelerate that fast, you don't need that much power, and it'll be quite a lot less stress on everything.

I use hubmotors, laced into small 20" wheels, one good and wide rim and one crappy and narrow rim, both good Sapim 13/14 butted spokes from ebikes.ca, no failures yet despite potholes and whatnot (even one curbstrike on the good rim). Not sure if that is your best solution, but it might be easier on your drivetrain than a chaindrive.

 

[Chalo]

Something to consider about thru-the-gears type of middrive, is that if you are using it with a freewheeling crank at the stoker, it's crank freewheel is going to have to handle the input from two people pushing a heavy trike, and it's not unknown for that freewheel to fail with just one person's input on a light bike. It's probably only a concern if you are riding without assist, or if you are heavily cranking on startup with minimal help from the motor, etc.

The thing that kills crank freewheels isn't pedaling; they are designed for that. What they aren't designed for, that trashes them, is freewheeling with tension on the chain. That happens when motor power is applied without pedaling along. The problem is that the bearing in a freewheel is only intended to spin when there's no tension on the chain-- when the rider isn't pedaling. So the bearing is loose, poorly finished, crude, and otherwise only suited to an easy life of spinning when there's no load. Add load while they spin, and they quickly self-destruct. The rest of the freewheel follows.

 

[dogman dan]

It's possible to get a good hub motor wheel, just a matter of buying your motor at the right place. But yeah, Chalo is right that your original wheel is stronger. Quite a bit stronger, since the motor wheel in 20" is likely to be a radial lace wheel. But it can be adequate, provided your wheel is not made with the cheapest spokes and cheapest rim in the entire world.

Since you do have a rim brake possible, a hub motor is possible. You mentioned that the ride kick got hot with the heavy load, and a hub motor can too. For that reason, I'd suggest one of the larger, heavier hub motors that have more copper and larger magnets. Tons of power you may not need, but it will be nice to have it once in a while when you do. The rest of the time, your big fat dd hub motor will run cool and efficiently, so no problems.

Except for the drag when you pedal no power. Easy solution, don't do that. No, I don't mean cheat all the time either. Simply select the lowest power level on your 3 or 5 speed switch. Then you just get a tiny tickle of assist. Enough to completely eliminate the drag, AND the extra weight of the big hub motor. Using your assist at such a low level will mean almost unbelievable range. Say you have a 48v 20 ah battery, it's got 1000 watt hours. So if you use your battery at 100w, you could ride for 10 hours non stop. So an hour at 500w, and you still have 9 hours left running at 100w.

I don't see the drag as a big problem. And, if you should break down and have to push that drag all the way home, the drag is proportional to your speed. You can hardly feel it at all at 8mph. Only at 15 mph does it get to be a big deal.

Over all, it just seems to me that the problems to solve with a hub motor are much less than the problems to solve with the mid drive.

But one thing we have not mentioned yet,,,, a left side, non hub drive. the motor, the belt or chain, all driving the rear wheel on a separate sprocket on the disk brake side of the rear wheel. That would be a home made thing, but it would work good. But no shifting of the gear ratio.

 

[amberwolf]

But one thing we have not mentioned yet,,,, a left side, non hub drive.

u sure? :wink:
https://endless-sphere.com/forums/viewtopic.php?f=3&t=75733&p=1143778#p1143719

 

[dogman dan]

Whoops. I definitely skim read too fast all the time.

I'm intrigued by the idea of a left side drive using a motor like this, but maybe a larger, more powerful version.


http://www.ebay.com/itm/KIT-ELECTRIC-MID-DRIVE-MOTOR-BRUSHLESS-48V-1000W-QUAD-CAR-E-BIKE-/191529528875?hash=item2c980cae2b:g:bLwAAOSwv0tVCAcn

 

[teklektik]

Regarding the wheel build:
Here's an observation by Justin re: radial lacing vs paired spokes...


(more on this discussion here for a 20" wheel build)

Regarding drag:
It may be a good plan to look for a DD motor with 0.35mm laminations as explained by Justin in this post:

My main interest in thinner laminations has ... to do ... with the reduced drag when you are pedaling with out the motor. At normal biking speeds eddie currents can easily be about 50% of the core losses that cause motor drag, and going to 0.35mm can take a big chunk out of this and allow the motor to freewheel better.

Although your budget is strained to get this together, I would add that as a 'futures' purchase you might consider a CA V3, simple PAS wheel, and adjustable pot for assist level - available plug and play from Grin Tech. This would automagically give you a 'background' assist to make the whole motor thing more invisible - anywhere from just enough to overcome motor drag or a 1-2% grade, to something to get you clipping along. This can be adjusted for smooth getaways and the infinitely adjustable pot (dial) lets you tweak the assist level to better match other riders, etc. Anyhow - just a thought to help preserve the present riding experience...