Electrifying my tandem bike

Hi,

I would like to electrify my tandem bike. I found another thread on this exact project here and it suggested a Smart Pie motor. But from my research on this forum, that internal controller is not very water proofed inside the motor. Therefore I started a new thread to see what you guys can suggest.

Bike + Rider = 145 kg after electrification, with no cargo.

Here's a picture of my tandem a few months ago. The only difference now is that I have a rack with panniers on it.



I would like something simple to install that looks clean. By looking clean I mean having stuff like a well packaged/hidden controller, water bottle battery, or some kind of nice packaging for the battery. I don't mind doing a little DIY, as I am quite handy, but I do not have access to a lot of fabrication tools. I live in Sweden and my budget is quite low, maximum 6000 SEK = 690 EUR = 924 USD = 593 GBP for everything I need.

Here the terrain is quite hilly, and I would like electrification for a lot of help on that. I would like to be able to average 25 kph on a typical journey, so that would mean being able to go faster than 25 kph with pedaling on the downhills and possibly flat roads as well. I am open to all suggestions, especially from people new to electrification as this will be my first attempt as well

Thanks!
Horace

EDIT: Added more information based on questions asked:

Both riders do not plan on pedaling lots. We usually take it really easy on the hills, low cadence and low effort. We would like to go faster though.

Frame is steel.
Rear frame spacing is 135mm. Front is 100mm.
Rear drop out width is 10mm.

I drew a picture of the rear. the 350 mm measurement is of the tire outer diameter.



Top speed really doesn't matter to me. But average should be around 25 kph. So the bike can either go up hill at 15 kph and downhill at 35 kph, or up hill and down hill at 25 kph. But I think the latter option is better. We would like more help up the hills when times are tough rather than the other way around.

I think 30 km range without pedaling will get me a round trip to pretty much everywhere around town. I would like to do long distance touring later on.

The things one might suggest is very relative, do both riders plan on pedaling lots? Because pushing two people with a bike and such up a hill could burn a motor out.

Either way, I'd probably suggest a vented and sprayed hub.

What is the frame made out of? What is the rear drop out spacing? See the gap in your picture of the bike just above where the rear wheel intersects with the frame at the top? Can you measure that gap as well? Another way of describing this location is just above where the rear brakes are located. Fat tires are very, very preferred. What is the dropout axle space width? Do you have digital calipers? Find out if the dropout is at least 135mm apart and each dropout can hold 10mm axles. What sort of ranges and top speeds do you hope to achieve or is this to solely be used as an uphill aid?

Hi,

Good questions.

Both riders do not plan on pedaling lots. We usually take it really easy on the hills, low cadence and low effort. We would like to go faster though.

Frame is steel.
Rear frame spacing is 135mm. Front is 100mm.
Rear drop out width is 10mm.

I drew a picture of the rear. the 350 mm measurement is of the tire outer diameter.



Top speed really doesn't matter to me. But average should be around 25 kph. So the bike can either go up hill at 15 kph and downhill at 35 kph, or up hill and down hill at 25 kph. But I think the latter option is better. We would like more help up the hills when times are tough rather than the other way around.

Making it neat depends a lot on your DIY skills. Unfortunately most of the bottle batteries can't give enough current for good hill-climbing. Your forks look a bit thin, so a 350w hub-motor would be as far as you could go on the front. A geared rear motor would give you what you want.

I've had a brief communication with another Sweedish guy. I know Sweeden is a big country, but it might be worth contacting him to see what he's doing. I think that he's considering a MXUS kit direct from MXUS.

http://www.pedelecs.co.uk/forum/introduce-yourself/15450-swedish-newbie-first-build.html

You might be able to share an order to reduce the shipping cost. MXUS do a copy of the Bafang CST motor, which would be a good solution for your bike. The motor has a spline for cassette gears, so you don't have to change anything on your gears, unlike most rear hub-motors. MXUS do a controller, throttle, pedal sensor and wiring to go with the motor-wheel, which makes a very neat kit. They call it the "anti water kit" (water resistant). The controller is a long thin sealed box which goes along a frame tube (normally behind the seat tube). The whole kit is very neat and well within your budget. The motor designation is MX01A. It's not in their catalogue. It comes in a range of speeds, so you should tell them what you want. 250 or 270 rpm for speeds of 32 or 35km/hr on a flat road with good climbing power. You can see their kits here:

http://www.mxusebikekit.com/shop_show.asp?cid=46

but if you want one, you should email Shine Wang. Her email address is mxus012@hotmail.com, and tell her that you want a anti water kit with the 500w MX01A motor, or make a joint order with Nusse because I think that he's getting the same. For that kit, you need a battery of at least 15aH to provide the current. Naturally, you get more power at 48v than 36v, but I think 36v would be OK with the 23 amp controller.

Hmm, another one who seems to want what we all do.

Cheap, small, discreet, but hauls two people up hills like something expensive, big, and obvious. It's the old dilemma, old as time. Name three things you want in a machine, then you can have two, not all three.

Oh well. One option would be a smaller, less than 400w planetary gear hubmotor. It will really disappear almost invisible behind the rear gears, and run fine on small inexpensive batteries like the bottle type. This option really does require some pedaling from both of you, or lots of pedaling from just you on the steeper hills. Climb a really steep hill too slow with hubmotors, and you can damage them. The smaller the motor, the easier to damage them. If you go this route, really try to keep it going 25kph up hills.

The other option is a bigger motor, bigger battery, more money. One very good choice for you would be a slower version of the MAC planetary gearmotor. Run it on a fairly big battery, and give it 1000w or so. Then you should be able to climb those hills as fast as you would like to. Still have to pedal, but it won't be real hard pedaling unless it's very steep. Still have to keep it going 25kph, but it will be 600w worth easier to do that.

I recommend go big for two people. Another way to go big, would be two small motors, and two bottle batteries. Better still, two big motors. But that just leaves cheap behind in another way.

Hi!

Thanks for all the tips so far. Do you guys have any suggestions on whether I should go geared or direct motors? Damage on a hub motor when going too slow - is that due to the gears receiving more torque? Wouldn't this be solved with a bigger, non-geared motor?

And just to clarify, the setup doesn't have to be small. I am OK with having a big looking, non-discreet motor. But I would like to have parts like the controller and batteries well mounted with not too many exposed wires. Clean looking, but not discreet.

Horace

HoraceLai said:

Hi!

Thanks for all the tips so far. Do you guys have any suggestions on whether I should go geared or direct motors? Damage on a hub motor when going too slow - is that due to the gears receiving more torque? Wouldn't this be solved with a bigger, non-geared motor?

And just to clarify, the setup doesn't have to be small. I am OK with having a big looking, non-discreet motor. But I would like to have parts like the controller and batteries well mounted with not too many exposed wires. Clean looking, but not discreet.

Horace

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Direct drive and geared have different pros and cons. Direct drive motors are heavier and have drag while free wheeling. The pros are they can take more wattage without burning up and are more efficient on flat sections. They also can do regenerative braking which with the added mass of a second rider might be practical in your case.

Geared motors are lighter, more efficient at hill climbing and stop/start cycling and they have virtually drag-free freewheeling.

Damage to the hub motors really depends on the wind, size of the motor and how many watts you are feeding them. Basically, in the scenario Dogman is talking about the greater the slope the more inefficient the motor becomes.

Let's hypothetically say you are pumping 1,000 watts into the motor on a really steep slope but you are only getting a 30 per cent efficiency. In other, words you are crawling up the hill. That means the vast portion of the watts coming from the battery is being converted into heat. What happens is the heat fries the electrical components such as Hall sensors and phase wires. If it is hot enough in a worst-case scenario it can even destroy the magnets.

A direct drive motor is better at shedding heat than a hub motor. The chances of melting gears in the other type are slim if you are running the correct amount of watts. For instance, if you are running 5,000 watts in a 1,000 watt-rated gear motor the chances are high you will ruin the gears assuming your don't fry other parts first.

As Dogman, said already the best set-up would be two 500/1,000 watt hub motors in each wheel. I don't think those forks could handle that size and ideally you want to have identical motors in a dual motor build. The second-best solution would be a 'torque' wind motor which has a slower speed and is less likely to build up heat while going up steep hills.

If you go with a slow wind rear motor you will probably be fine. However, it will need to be 500 watt rated to address your performance criteria. You will probably need at least a kilowatt/hour of battery although you haven't mentioned range yet?

I find putting the wires in an old cut-to-measure bicycle tube to be a great way of cleaning up the build and it prevents the connectors from getting wet or experiencing snow. I do think your budget is too low. I'd say €1,000 to €1,200-all in, is more realistic. I have an 8 turn MAC geared motor and have found them great at carrying my bike (40 to 50 kg), me (65 to 68 kg) and a trailer (up to 90kg but normally 30 to 40kg) around relatively flat ground with modest short hills of about 300 metre lengths max. I'd suggest a higher turn motor would be more suitable for hauling two people.

Once you have selected the motor the single most important component is the battery. Really it is nearly all about the battery which will eat most of your budget.

As mentioned above - I think you have a funding issue....

Ignoring that, you have a nice light fast tandem, but the front fork looks too light for any serious power. Dual motors are possible, but you would need two controllers, so with budgetary considerations - go with RWD. I think you should seriously look at a 10T or possibly 12T MAC and just throw the battery in the pannier. If you get a 48v battery from cell_man he can split it for you - or get two 24v. Since this is a big horse tandem anyhow, the extra weight back there isn't going mess up the feel to the extent it might on a single seater.

Here's some info on MACs:

A consideration for going with one of these larger gear motors is that they have essentially indestructible gears and the larger size will give you some lattitude in heating compared to a small geared motor. MACs from cell_man are now coming through with a new stronger clutch design similar to the BMC V4. The 9-FET controller is a good safe match out-of-box, but you might consider the 12-FET and program it back a bit to give yourself some headroom for heat and future growth. I think cell_man would downgrade the current limit for you specially, but buy a programming cable anyhow. Email him about your application and see what he thinks is the best controller.

You could hang the controller under your rear rack and with the panniers to hide the MAC, all will be hidden.

A plus for the gear motor is that if you need to get a more modest battery for budget reasons, you can shut off the motor and just pedal on the flats and there will be no motor drag because of the internal freewheel clutch. It will ride like a regular bike but with a bit of extra weight...

Joseph C. said:

As Dogman, said already the best set-up would be two 500/1,000 watt hub motors in each wheel. I don't think those forks could handle that size

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If that's really a tandem-rated fork, then it can handle a hub motor better than anything you are familiar with.

I think 30 km range without pedaling will get me a round trip to pretty much everywhere around town. I would like to do long distance touring later on.

The forks should easily handle up to 1000w of motor, with proper installation and at least one quality torque arm.

Budget is a definite issue. But if the hills are not so severe or long, even the small gearmotor can be a good addition to your bike. You would perhaps need to rest the motor for a long time after you heat it up, but you can stop in time if you have an affordable remote thermometer attached to the axle. At some point, you see above 110F on the axle, and you know to let the motor cool. Gearmotors take forever to cool, but you could still have some hill assist when you need it, depending on the terrain.

The main thing I wanted to make you aware of, is that affordable lower powered bike motors only do so much and no more.

The heat problem is caused by the fact that a hubmotor is stuck in one gear. So if the full power is applied, but the load is too much to allow about 15 mph of rpm, then the motor melts if run long enough.

If you do get a small hubmotor, try to find one with a low rpm specification. It will be slow on the flats, but able to climb steeper hills without damage.

Another option not mentioned so far, is a motor that drives your bike chain. That allows using the bikes lower gears. With those, you can gear down and crawl up hills slow. But they are not discreet like a small rear hubmotor.

Okay. I see. Great comments. I would also like to add that my friend has an electric single seater bike with 250W geared motor and 36V/10Ah battery. The terrain he rides it on is the same as mine. I've tried his bike on the hills that I go on. With low battery levels, and me lightly pedaling (no sweat), I was able to get up a steep hill easily. I was probably going 11 to 12 kph, and with my non electric single seater road bike I have to pedal at around 7 kph to not sweat.

Here is what I have decided so far.

Either RWD. The fork issue is a bit of a concern and I also think non-FWD allows more room for expansion.
Around 500W hub motor
Not sure about battery really. Maybe something close to 48V and 10 Ah?

Recommendations on kits and options would be great. The ones posted earlier has too many options that I do not really understand.

I have done research on mid drives before posting on endless sphere. I do think they are discreet enough. For me, it doesn't have to look stealth, it just needs to look clean, like things are properly clamped and mounted and not zip tied. My main concern with mid drive is where to put the motor. Pretty much all the bikes I see show the motor being the lowest part of the bike. I need the clearance in the middle of the bike because of a ramp that I use to take the bike into the basement. I have to put my pedals in the 9 and 3 o'clock position for my tandem bike to clear it.

HoraceLai said:

...my friend has an electric single seater bike with 250W geared motor and 36V/10Ah battery. ... I've tried his bike on the hills that I go on. With low battery levels, and me lightly pedaling (no sweat), I was able to get up a steep hill easily.

Click to expand...

That was a major piece of information to set the scale of recommended solutions.....

Do you guys think it is more economical to have the regen braking on direct drive motors or the free wheeling and better climbing performance of the geared motor when it comes to a tandem?

HoraceLai said:

Do you guys think it is more economical to have the regen braking on direct drive motors or the free wheeling and better climbing performance of the geared motor when it comes to a tandem?

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If you intend to spend any substantial amount of time pedaling without power, then a freewheeling motor is the way to go. I have seen an analysis by Justin Elmire of Grin Technology that concludes you can get more miles per kilowatt-hour by using regen and powering just a little to offset the additional drag of the direct drive motor-- but pedaling against the drag of a completely unpowered DD motor is simply disheartening. I'd sacrifice a little bit of motorized range just to have a bike that was satisfactory when not on the juice.

I think you will need more than 250w. With two people on the bike, and one not pedaling much, you will tend to bog down slow enough to fry a smaller motor on a big hill. I think you will just kill a tiny gearmotor if you ride up hills less than 12 mph. Bog a hubmotor down too slow, and 80% of the power just makes heat. Meanwhile, getting only 20% of the power down to the road is not helping you worth a damn. You need a motor big enough to haul two butts up a hill.

I still think a more powerful motor would be best for you, but then.... more money. I'd say a MAC in a slow winding (12t) would be good, but you can run it on a smallish 20 amps controller so you don't have 1500w, causing you to spend a fortune on the battery.

A freewheeling gear motor might very well be best for you, so you can pedal without resistance on the flats, saving your battery for the hills, or big headwinds when you need it.

I nearly never recommend RC lipo aka lico batteries for newbs. But if you will only use the motor when you really need it, RC lipo batteries can be a good choice. A very tiny and light 5 ah pack can power a big motor for about 4-5 miles. This would give you lots of power on that hill, but not a lot of weight, size, and more importantly expense.

Research Lico very carefully, since improper charging in an unsafe place can burn a house down. Other types would require carrying up 10-15 ah of battery to power a larger motor. A good lifepo4 can cost 500-800 bucks.

HoraceLai said:

Top speed really doesn't matter to me. But average should be around 25 kph. So the bike can either go up hill at 15 kph and downhill at 35 kph, or up hill and down hill at 25 kph. But I think the latter option is better. We would like more help up the hills when times are tough rather than the other way around.

Click to expand...

Math isn't quite right here since you spend more time going up hill. for a 15 km hill, you would spend an hour going up it, and .43 hours doing down it, with an average speed of 30km/1.43 hours = 20 kph.

When I was using a direct drive motor, my speed up hill was faster, down hill was slower (from cogging), and my total speed was faster.

dogman said:

I still think a more powerful motor would be best for you, but then.... more money. I'd say a MAC in a slow winding (12t) would be good, but you can run it on a smallish 20 amps controller so you don't have 1500w, causing you to spend a fortune on the battery.

Click to expand...

This is sort of where I was at in the post above. Kind of a hard call considering the budget. Here is an example buy from EM3EV for a 12TMAC and 10Ah battery. Paul could split the pack in half for your panniers for a nominal charge.


Since you have road brakes, I left off the MTN ebrakes and went with a 9FET controller instead of 6FET to give you a little heat/expansion headroom. The wheel is CNC for your vbrakes. Paul sells a triangle battery with slightly higher capacity and, of course, there are other battery vendors as well.

You will need a modest charger, freewheel, torque arm, and maybe a couple of spacers. Shipping will eat up a fair amount of money but this works out close to your budget. Anyhow, it's something concrete to discuss as a possibility - perhaps others can put out some other package options......

Hi guys,

I have checked out packages from both Em3EV and Golden Motors and it seems like the kits are more complete with GM. The torque arms on the EM3EV site are $40. Overall it seems easier with GM but I am unsure of their quality. Any comments? They recommended me to get the Magic Pie 3

Horace