Wheelchair tandem bicycle advice to add power assist

[Ericjo]

I recently purchased a "duet wheelchair tandem bicycle" so my son could enjoy bike rides and to use for transportation in nice weather. It is a wheelchair inplace of front bicycle tire with the back 1/2 of a bicycle
. The version i purchased is a 3 speed bicycle with coaster rear brakes and front brakes are hand operated brakes on the wheelchair tires. I desire to pedal most of the time but need some power assist for hills or longer trips. I am 160 lbs. Wheelchair is 60 lbs and passenger is 110 lbs. I am a novice so excuse my lack of knowledge. The company that makes this bike offers a powered version but it is nearly $4,000.00 beyond the base model price and and "upgrade" consist of replacing the bicycle portion with the powered bicycle portion at nearly $4,000.00 well beyond the afforability of a disabled childs family. I am limited to an option that adds power to the rear bicycle tire. My son has multiple disabilities, physical, cognitive and visual.... his joys in life are movement and music.... he long ago outgrew a rear childs bicycle trailer so im so excited to take him biking in this wheelchair tandem. Appreciate all advice. ☺ attached are stock photos of the bicycle, i'm happy to provide any detail photos of mine if helpful.

 

[zackclark70]

should be as simple as a geared rear hub or a mid drive motor if your planing any hills i would go mid drive the thing is getting 100% reliability will be hard for a first ebike

 

[Drunkskunk]

Welcome to the forum.

There are 3 minor complications to using a conventional hub motor on that bike:
-The width of the frame is narrower than what most hub motors need.
-A hub motor would eliminate the coaster brake, so you would need to devise some other form of braking.
-Hub motors are less efficient at the low speeds you might desire on a bike like that.

The alternative is to use a mid drive. They replace your front gear and pedals, and allow you to keep your 3 speed, coaster brake, and rear wheel. they allow you to pedal all you want, and add power as you need it, and can take advantage of the 3 speed hub for extra help up hills.

The best and simplest to install would be the Bafang BBS line. I think a BBS02 is about right for your needs. several vendors carry them. Here's one: https://lunacycle.com/bafang-bbs02-750w-mid-drive-kit/

 

[The fingers]

Plenty of battery space.

 

[fechter]

The coaster brake won't work with a Bafang BBS drive, but otherwise it would probably be the best at low speeds. It may be possible to add another type of brake on the rear.

Not sure if there are any geared rear hub motors that would fit the rear dropouts. We might need a measurement of the bike to know for sure. Not the easiest thing to measure, but the distance between the two rear dropouts that hold the rear axle. Hub motors come in different widths.

 

[Rassy]

I agree that a BBS02 would be an ideal system to mate with the IGH. Most tadpole trikes do not even come with a rear brake, so if the wheelchair brakes are/can be operated from the bicycle (best if independent) the braking should be adequate. It may be possible to "operate" the coaster brake via a brake lever system by pulling up and engaging a cog on the rear freewheel and nudging it backwards or some such thing. Maybe someone has already solved this problem?

Edit: From the picture I'm pretty sure the wheelchair brakes do operate from the bicycle.

Edit: Here's an idea how one might be able to operate a coaster brake after installing a BBSxx crankdrive, sort of taken from the way a Schlumpf high speed crank set is shifted by using your foot/toe. Replace the 5 screws that hold the chain wheel cover on with through bolts that each have a small "tab" on the crank side. The tab could just be a number of washers on the bolt. Then to activate the coaster brake slide your foot over to catch one of the tabs during the down stroke as you pedal backwards.

 

[amberwolf]

There are also clamp-on braces for the seatstays that add V-brake bosses to put rim brakes on the back wheel. There's a thread about a trike (worksman?) where someone needed to do that, around here on ES somewhere.

 

[dogman dan]

I would vote for the bafang mid drive. Then possibly add a rear v brake to the original wheel. If not possible, experiment, see if just the fronts will work for you.

Front brake works best anyway, and it won't skid sideways and lay you down like too much front brake can on a regular bike.

Cool bike by the way.

 

[Rassy]

If v-brakes were added to the rear wheel, there would still be a problem mounting/using the brake lever. It would have to be removed from the handlebar when the wheelchair is separated from the bike part. Not sure how the chair brakes are operated, but if they require two hands and a balanced pull on each there would not be an easy way to also pull the rear brake lever.

I do believe the front (chair) brakes would be adequate, but there would not be any real cost or modifications necessary to adapt foot operated tabs to the front chain ring that would allow for the use of the existing coaster brake.

 

[dogman dan]

I would try just the chair brakes for sure. To separate the two, that also means it would be a hassle to disconnect e brake handle wires, display wires, throttle wire if any, etc etc.

But you don't have to have e brakes, or one wire on one brake is easy to connect/ disconnect. Have Pas, and put the display on the back. You can still use it, but really don't have to stare at it the whole ride.

If you went to a hub motor, then you could use a regen brake in back. Then the one e brake handle, or pushbutton, that is easy to disconnect, could control that brake and also cut power when you need it to happen. With a hub motor, you'd have to go to one gear, or add a derailleur for 7 gears.

 

[Ericjo]

Yes, the wheelchair brakes act as the front brakes in "bicycle mode". The front brakes are controlled by a bar so they are engaged together vs left/right independently.
Any thoughts on a "friction drive" motor? As i came across this i thought it may be the easiest to add.
I really desire something that i can use to climb a hill, i don't mind if i had to dismount to turn it on/off. Presently I'm needing to dismount and walk uphill because i just dont have the strength to sit and pedal uphill and the design prevents standing and pedaling.
I will need to involve a bike shop or mechanic once I've decided on a strategy/product to use.

 

[fechter]

Friction drive might not be a bad idea. At least you would be able to keep the coaster brake and not need to replace anything on the bike. Friction drives are pretty limited power wise but if you are mainly on flat ground or mild hills, it might be the way to go. There aren't many choices in the market for those though. The ones Kepler makes look like the nicest ones I've seen.

https://endless-sphere.com/forums/viewtopic.php?f=31&t=86961&hilit=drive

 

[spinningmagnets]

It should be very easy to add a reliable hubmotor kit for under $1200. What is the width between the rear drop-outs? (You may have to remove the rear wheel to measure that)