Folding Python delta trike

The forces on that BB are considerable , I tried fastening one with a pair of bolts @ 90' to each other [ M8 or M10 ] in steel and within 30km it was visibly moving when pedalled.
If using aluminum you can't use a rescued shell anyway.
things to take into account :-
BB axles are longer on one side than the other so the distance from the end of the BB axle to the centre of the BB is not half the BB shell width.
Chain sets have different off sets also IIRC 0mm / 3mm or 6mm
You may need a pedal on the other side that has a bend in it [ MTB ] rather than straight [ road bike ] for your ankle bone to clear the front frame.
Paul
 
Thanks again for the input guys, this saves us a lot of trouble when we actually start building. I've updated the BB design by putting a slit in top of the aluminium square tube, and extending the sides to allow for one or two clamping M8 bolts at the top. Also updated the BB shell from 40x2.5 mm tube to 40x3 mm because that universal BB should fit a 34mm hole. I think I'll go with the design with two bolts and the longer aluminium square tube.
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My inseam is 89 cm so the distance from the end of the seat to the BB could be about 76 cm according to the Python project survey. It was too short in my original design, I've now extended it to 71 cm. But even if it were a little shorter, the pedals don't reach the wider part of the frame (circles show travel of the 170 mm cranks), so I don't think I need a bent crank on the left side. I've drawn a 44T front chainring; HP Velotechnik uses a 44T & 16T with the Shimano 8 speed gear hub on their 20" recumbents, so I'll go with that too. The chain runs nicely under the wheel frame. Wheel frame is 40x10x1.5 mm steel tubing, BB arm is 35x35x1.5mm steel. Still haven't designed the seat.
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Lining up the front and rear chainrings is no problem, because we can take that into account when welding the BB arm to the wheel frame. But I'm still not sure how to select the right BB axle length to get the pedals the same distance from the center.
 
I think I'll go with the design with two bolts and the longer aluminium square tube.
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Yep 2 bolts better

But even if it were a little shorter, the pedals don't reach the wider part of the frame (circles show travel of the 170 mm cranks), so I don't think I need a bent crank on the left side.

it's not the pedals that might hit the frame but your angle/heel/shoes etc

But I'm still not sure how to select the right BB axle length to get the pedals the same distance from the center.

One side of the BB axle is longer to accommodate the rings especially if you chose a triple.
On mine I needed the maximum offset possible [ inwards ] to get the chain to have a sensible angle.
The front rings are almost over the BB shell that are so far to the left. I can take a picture if needed.

Paul
 
it's not the pedals that might hit the frame but your angle/heel/shoes etc
Thanks Paul, I understand. The wheel frame at 100 mm is narrower than the BB axle, and there is already a bit of a bend in the cranks, so I'm not too worried about hitting the frame.

One side of the BB axle is longer to accommodate the rings especially if you chose a triple.
On mine I needed the maximum offset possible [ inwards ] to get the chain to have a sensible angle.
The front rings are almost over the BB shell that are so far to the left. I can take a picture if needed.
Thanks, I think I understand what you mean.
I found the specifications of the BB I want to go with. Up to 116 mm, the protruding ends are the same length, at longer lengths it's asymmetrical but only by a few mm.
The 44T crank set I want to go with has a -2 mm offset, so it's also going a little inwards towards the BB. I can't find any chainline numbers though.
The gear hub I'm probably going with is a used SG-8R36 Shimano 8 speed with roller brake. OLD is 132mm, and the chainline is then either 42 mm or 48 mm depending on which way I mount the dished sprocket.

Maybe I'll order the crank set first and measure it, and then order the right axle length BB later.
 
The 44T crank set I want to go with has a -2 mm offset
If you want to use a 44T front chain ring with a 5 speed cassette, normally 14-28, you will have a slow bike.
I started with a 48/38/28 front and 11-30 8 speed cassette and that combination was to slow. I changed it to a 52/34 and which is acceptable, but some time I wish I had 54 or more. With my combination I rarely use the 2 lowest gears when climbing, but always the highest gear on the flat.
When I climb, living in the hills, I lose traction, on asphalt, when the incline is around 14deg or more, common around here.
 
If you want to use a 44T front chain ring with a 5 speed cassette, normally 14-28, you will have a slow bike.
I started with a 48/38/28 front and 11-30 8 speed cassette and that combination was to slow. I changed it to a 52/34 and which is acceptable, but some time I wish I had 54 or more. With my combination I rarely use the 2 lowest gears when climbing, but always the highest gear on the flat.
When I climb, living in the hills, I lose traction, on asphalt, when the incline is around 14deg or more, common around here.
Ok let's do some calculations. Your old top gear was 48:11 and your bottom gear was 28:30. With 20" wheels, you move 1.49 to 6.96 meter per full crank rotation.
If you're in top gear at a cadence of say 60 rpm, that's 25 km/h, at 80 rpm that's 33 km/h.
I see what you mean.

I'm going with a single 44T at the front and a single 16T at the back, and a Shimano 8 speed internal gear hub. According to HP Velotechnik this gives a range of 2.19 m to 6.64 m per full crank rotation.
In top gear, a cadence of 60 rpm gives 24 km/h, 80 rpm gives 32 km/h, 100 rpm gives 40 km/h.
But I'd rather cruise in the more efficient 5th gear (1:1, 4.39 m). Then 60 rpm gives 16 km/h, 80 rpm gives 21 km/h, 100 rpm gives 26 km/h.
I have pretty torquey legs (once sheared a pedal off the crank) so I probably won't ever use the lower gears, especially since I don't plan on doing much hill climbing at all (Netherlands is flat).

So yeah that's indeed a little slow and I could easily go with a bigger front chain ring. And I just ordered a 44T crank set :(
 
I have pretty torquey legs (once sheared a pedal off the crank) so I probably won't ever use the lower gears, especially since I don't plan on doing much hill climbing at all (Netherlands is flat).
That does depend where you cycle ? around Arnhem it is pretty hilly and lots of the coast near Belgium has major up and down ramps for the sea wall ?

So yeah that's indeed a little slow and I could easily go with a bigger front chain ring. And I just ordered a 44T crank set :(
Could you change out the 16T for something with less teeth ?

Paul
 
That does depend where you cycle ? around Arnhem it is pretty hilly and lots of the coast near Belgium has major up and down ramps for the sea wall ?
I'm actually quite near Arnhem. I live in between two hills; the "Wageningen hill" is a 17 meter climb with an average grade of 6%, and the Grebbeberg is a 37 meter climb with an average grade of 5.5%. So yeah it's not completely flat, but those are about the steepest I've ever climbed and I couldn't imagine a 14% grade hill! To be honest, I avoid climbing hills.

Could you change out the 16T for something with less teeth ?
Unfortunately the 16T is the smallest that fits with the gear hub.

I guess I can just return the 44T crank set. Biggest single I can find is 52T.

Edit: China has up to 58T. A 56T sounds nice because it would give about 20 km/h at 60 rpm in 5th gear. I'm a little worried about aluminium chain rings though. If it really is 7075-T6 it shouldn't wear too quickly, but it's a very brittle material and it's at the very front of the bike. I'd have to extend the frame a little so that it wouldn't be the first thing to hit for instance the shed wall.
 
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I missed that you considering using shimano 8 gear hub. I'm using the same hub on my chopper and, at the moment, the coaster brake is the only brake I have, I'm only doing test rides, and it works ok.
But on a python, can you use a coaster brake? In an emergency?
I have the 8cd version so I can ad a disc if needed.
 
I stand corrected, roller and coaster brake is not the same thing. Can you tilt the roller brakes or are the fixed with the controls input at the front?
Which is on the wrong side on a python.
 
I stand corrected, roller and coaster brake is not the same thing. Can you tilt the roller brakes or are the fixed with the controls input at the front?
Which is on the wrong side on a python.
Not sure what you mean. The shifting cable and roller brake cable are on opposing sides, and need to go away from the chain instead of in the same direction compared to an upright bike. But can't you just rotate the hub 180 degrees so it is upside down, or however many degrees so the cables go in the right direction? I'll need to make custom brackets anyway.

Looking at FWD recumbent with IGHs for inspiration, I found this Python with a Shimano Nexus 7 gear hub and presumably a coaster brake. They use the largest chain ring on a triple crank set, it looks to be 50+T.
jpgQEnJc8e3pv.jpg

And I found this RWS trike (Jouta XX) with a Shimano Alfine 8 gear hub with disc brakes. It comes with either a 57T or 60T (!!) front chain ring.
Jouta-XX.jpg


So a FWD Shimano IGH is possible but probably best to go with a larger front chain ring than 44T.
 
But can't you just rotate the hub 180 degrees so it is upside down.

It's not that simple, the hub comes with different colored spacers which gives different angles for the shifter wire compared to how a normal bikes rear wheels is fitted.
It's also sold for different shifter angels, so get the combo which suits you.
I hade to make my own to get the angle I wanted.
If you get a horisontal gear shifter position and a horisontal brake position you can flip the hub.
But remember if your slot for the front wheel is vertical, a hub with a horisontal shifter position is not horisontal on your bike.
Otherwise you have to play with the angle combination which suit you best on the gear and the brake side.
 
I make those spacers/keyrings on order. Whatever angle is needed, no problem.

Also, the Nexus 8 is a tad cheaper than the Alfine, and does the job fine.
 
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