Converting a tandem trike

[RobF]

I think I've just answered my own question.

http://www.eclipsebikes.com/bafang-8fun-bbs01-drive-250w-motor-p-1102.html

This looks like it could be the best and simplest option.

The motor/crank is one piece, so there is no choice as to how close it is.

The BBS kit is well-regarded, so if it can be made to fit, it will do a good job.

I share trex's concerns that it will hang too low.

Your trike is not standard mechanically, so there could be other wrinkles which will be hard to overcome.

If you buy the crank kit and try to fit it, you may spend a lot of time and money finding out why the manufacturer uses a rear hub motor.

 

[Nealh]

The BBS sits approx 120mm under the BB and fitting allows it to be positioned at any angle so it can be tilted forward as far as possible also the bottom of the chain guard looks like it sits about 100mm below the crank so the BBS and chain guard may well have near the same ground clearance.
Ground clearance shouldn't be much of an issue unless of course you go offroad .

 

[Nealh]

Your location may help David as a member may be near you who has a 2 wheel BBS conversion for you to look at and take some measurements.

 

[Geebee]

If the pedals clear the ground so will the BBSXX plus it will be between the wheels so the only way to get hit would be to straddle a large boulder or similar.
One of my trikes has 2" ground clearance in about the same area and it causes no issue.

 

[David Stanbridge]

The ground clearance will be 125mm with the motor hanging straight down, and I've no plans to go off roading on it!

Do both brake cut off switches have to be fitted, as the bike has a coaster brake?

I'd be looking at placing the battery towards the rear, which is generally heavier, the battery or the motor?

 

[RobF]

Which bottom bracket do you intend using?

If the front, the co-pilot will have control over pedal activation of the motor, or are the two sets of pedals linked with no freewheel?

I suppose you could run the throttle to your bars and, possibly, set the motor to be throttle only.

Even then, you would need the front pedals always engaged to get any drive from the motor.

Eclipse sell a freewheel crank that might be of use.

Mounting the motor on the other bottom bracket could be problematical because of the two chain rings.

 

[David Stanbridge]

I'd be looking at mounting the motor on the front bottom bracket.
The two sets of pedals are linked with no freewheel, so captain or co-pilot can activate pedals.
The throttle, display, gears, brakes and steering would be on rear handle bars.

 

[shemozzle999]

You need to check the number of teeth on the front chain wheel and match it to those available for the BBS, also you might need an extension cable for the speed sensor which will have to be located on the rear wheel - they are also available.

 

[David Stanbridge]

The current chain wheel has 38 teeth.

 

[David Stanbridge]

Does anybody know the smallest chain wheel available, or maybe another motor with a smaller chain wheel.

 

[David Stanbridge]

http://www.ebikeclub.it/shop/en/accessories/30-chainwheel-38t-bafang-middle-motor-bbs01-bbs02.html

Anybody used these?

 

[David Stanbridge]

http://www.ebikeclub.it/shop/en/accessories/30-chainwheel-38t-bafang-middle-motor-bbs01-bbs02.html

Anybody used these?

 

[trex]

...
The two sets of pedals are linked with no freewheel, so captain or co-pilot can activate pedals.
The throttle, display, gears, brakes and steering would be on rear handle bars.

if the rear cranks turn without a sprag clutch, when the motor is engaged, the front chain ring will turn, the rear set of pedals will also turn in sync in order to power the rear wheel. This is dangerous.

 

[David Stanbridge]

Why?

 

[trex]

can you confirm that if you sit at the front, the rear pedals move when you pedal?
if this is the case, imagine you sit at the rear and turn on the throttle, your feet will move and your brain does not control them.

 

[David Stanbridge]

Okay, there maybe a little confusion re: no freewheel.

All four pedals move in unison.

If you turn on the throttle, this doesn't automatically move the pedals does it?

 

[trex]

if you sit in front and the motor is in front, you will be safe.
When you throttle up, the motor runs, the front chain moves but the front pedals don't move because the front cranks have clutch.The rear pedals move with the front chain.
Some body sitting at the rear can't control his feet and you will lose the rear back brake.

 

[David Stanbridge]

rear BPM hub motor is best for it.

Looks like you were right first time

 

[David Stanbridge]

So....rear hub motors.

Am I right in saying I'll need a new rear brake, and deraillier gears or no gears?

 

[Nealh]

Even with hills advisable to have some gears with a hub motor and yes you will need a new rear brake set up.