The final recumbent trike.

[th62]

Really cool. On my too long "I wanna" list. Any lessons to pass on about steering geometry?

Oh I learn't plenty from building around 12 recumbents, that's not to say they will suit you! Lets see, First was no more than 42 degrees backrest angle, sore necks proliferate at anything more, but that could be due to my cervical spondylosis. No more than two or three degrees caster or camber, any more will scrub out the tyres pretty quick. If you use tie rod ends, use a left hand thread on one and a right hand thread on the other. Just makes adjustment easier. Steering type is a personal choice, but I found tank/lever steering the best, under seat steering works ok too, but not as well as tank. Your need the crank around 150mm higher than where the seat meets the backrest, anything more or less makes it a little uncomfortable. Try out different squab angles to suit your bum, you also need lumbar support or your back will suffer. It's also a good idea to have the backrest in two parts with a gap in between, so the seat back doesn't rub against your vertebrae, flat seat backs are terrible. If you are young, you will need either a really big chain ring or intermediate gearing to raise the gearing. Pedalling cadence should be slower than on a diamond frame, pedalling fast on a recumbent will send you swerving all over the place. Back brakes are useless, don't bother with them. Place the seat as near to the rear wheel as you can get, the further the seat is away from the rear wheel, the more rear wheel slip you will get. Of course that means having a longish boom, the further back the seat the longer the boom will need to be because of the positioning of the cross beam. Try getting out of the frame with the crossbeam leading to the front wheels at different positions. Too far forward and you won't be able to get out of the thing without jamming on the brakes and allowing the momentum to throw you forward and out, too close to the seat will put more weight on the front wheels and less on the back leading to rear wheel. Slip.. You need Ackerman, without it it will understeer and scrub out tyres. Square tube is stronger than round, particularly around joins. Design something that uses as little metal as possible, it all adds up to weight. Two wheelers are a lot faster than trikes, tadpole trikes are stable, two wheels at the back are unstable and will tip easily. You don't need padding on the backrest if it is shaped to your back, but padding is nice under your bum. Delrin makes for good bearings in the kingpins and steering bars because it is light and seems to wear forever. Same with chain idlers, just make sure the chain idlers run in high speed bearings and the chain run is as straight as you can get it.
Thats about it, keeping in mind, everyone is different what suits me may not suit anyone else.
I've attached some build pictures that may help, along with a couple of earlier builds. The two wheeler was never finished, fell off and gashed my head and leg, the wife then convinced me to concentrate on trikes. I followed the two wheeler up with the trike minus rear suspension. It worked fine, but had plenty of wheel slip due to seat being too far forward and crossbeam too far back.

 

[th62]

Previous builds.

 

[savarin]

nice bikes, cant beat bents.
Built this for a mate, a retro style caravan with 2x12V batteries and a 500W dc motor. Pushing the trike along.

He had a small loudspeaker inside so when anyone asked what was inside he pressed the switch and a dog barked.

 

[th62]

I bought a car to tow one of them, easier on the legs, and you don't get wet.

 

[Shiseiji]

Oh I learn't plenty from building around 12 recumbents, that's not to say they will suit you! Lets see, First was no more than 42 degrees backrest angle, sore necks proliferate at anything more, but that could be due to my cervical spondylosis. No more than two or three degrees caster or camber, any more will scrub out the tyres pretty quick. If you use tie rod ends, use a left hand thread on one and a right hand thread on the other. Just makes adjustment easier. Steering type is a personal choice, but I found tank/lever steering the best, under seat steering works ok too, but not as well as tank. Your need the crank around 150mm higher than where the seat meets the backrest, anything more or less makes it a little uncomfortable. Try out different squab angles to suit your bum, you also need lumbar support or your back will suffer. It's also a good idea to have the backrest in two parts with a gap in between, so the seat back doesn't rub against your vertebrae, flat seat backs are terrible. If you are young, you will need either a really big chain ring or intermediate gearing to raise the gearing. Pedalling cadence should be slower than on a diamond frame, pedalling fast on a recumbent will send you swerving all over the place. Back brakes are useless, don't bother with them. Place the seat as near to the rear wheel as you can get, the further the seat is away from the rear wheel, the more rear wheel slip you will get. Of course that means having a longish boom, the further back the seat the longer the boom will need to be because of the positioning of the cross beam. Try getting out of the frame with the crossbeam leading to the front wheels at different positions. Too far forward and you won't be able to get out of the thing without jamming on the brakes and allowing the momentum to throw you forward and out, too close to the seat will put more weight on the front wheels and less on the back leading to rear wheel. Slip.. You need Ackerman, without it it will understeer and scrub out tyres. Square tube is stronger than round, particularly around joins. Design something that uses as little metal as possible, it all adds up to weight. Two wheelers are a lot faster than trikes, tadpole trikes are stable, two wheels at the back are unstable and will tip easily. You don't need padding on the backrest if it is shaped to your back, but padding is nice under your bum. Delrin makes for good bearings in the kingpins and steering bars because it is light and seems to wear forever. Same with chain idlers, just make sure the chain idlers run in high speed bearings and the chain run is as straight as you can get it.
Thats about it, keeping in mind, everyone is different what suits me may not suit anyone else.
I've attached some build pictures that may help, along with a couple of earlier builds. The two wheeler was never finished, fell off and gashed my head and leg, the wife then convinced me to concentrate on trikes. I followed the two wheeler up with the trike minus rear suspension. It worked fine, but had plenty of wheel slip due to seat being too far forward and crossbeam too far back.

Thank you very much! Lots in a very succinct post! Can't ride a diamond any more, won't go into the dirty details. Have never considered anything other than a tadpole. Sadly I moved literally cross country from the bike coop where I volunteered for a decade losing my basically free parts source. I noticed many if the details you mentioned in the picture you posted. About the only thing I don't care for on this forum is, as far as I can tell, you can't get a listing of a members posts to look back through what they have already passed on. Again, thank you.

 

[Shiseiji]

http://www.eland.org.uk/steering.html his spreadsheets are the best way to check on this as sometimes only 1mm makes a huge difference in handling.

Oh cool!!! Thank you. Yes, my limited research showed me just how critical it all is and why I asked that specific question. Definitely a place to use something like a frame board and jigs.

 

[savarin]

About the only thing I don't care for on this forum is, as far as I can tell, you can't get a listing of a members posts to look back through what they have already passed on. Again, thank you.

Hi Shiseiji, go to search, just input the name of the person whose posts you want to look for in the "by: member box", leave the "search box" empty and press search.
But, it looks like it only goes back 10 pages worth

 

[th62]

I don't use jigs and plans. The closest. I came to a plan or jig, is the large sheet of cardboard on which I drew some lines to get the angles reasonably correct. The frame came out nothing like the cardboard drawing, things tend to change as you progress, think of different design considerations and so on. To get sizes and angles, I set up some bricks and a couple of boards in a seat shape, sat down and got the wife to measure with a tape measure and angle finder. For the lumbar support, I took off my shirt, leaned back against the board and got the wife to trace the shape of my back against another board to my side with a permanent marker.
For pedal to seat distance, I sat on the makeshift seat, lifted my foot up another 150mm. And got the wife to measure between my instep and where the squab meets the seat back.
Jigs are great when manufacturing things in quantity, for one offs, I find they are not of much use.

Incidentally, make sure your heel is well clear of the ground when setting the crank height. An easy thing to miss, so I found on earlier builds. That will dicatate the height of the seat also, unless you change the seat height to crank height ratio. I think my builds were all around 100mm to the bottom of the chassis. I opted for the lowest seat height I could get to aid handling.

On my very first build I only had rear brakes, Big mistake, rear brakes on recumbents simply do not work at all. When you apply brakes, all weight is transferred to the front wheels, making rear brakes pointless. I also fitted a flat board seatback on the first build - Oh, my aching back, also wore the skin off covering my backbone. Not recommended at all, unless you have a mesh seat or a well padded seat back. I used a joystick steering system on the first one, it worked great, but, nowhere to place brake levers and gearselectors, so I had to weld a tube off to the side to mount brake levers and shifters on. On the plus side, this red one was extremely fast, the only thing stopping me going faster was the relatively low gearing.

 

[RandyM]

Hi Shiseiji, go to search, just input the name of the person whose posts you want to look for in the "by: member box", leave the "search box" empty and press search.
But, it looks like it only goes back 10 pages worth

Or, go to his profile page and select the posts tab.

 

[Shiseiji]

Thank you Randy! Appreciate it.