New 'bent

DIscuss anything relating to non-standard cycles and their equipment.
Joe.B
Posts: 270
Joined: 13 Nov 2010, 11:31am

Re: New 'bent

Post by Joe.B »

Hi Bob,

Congratulations on the new Rapto, I've only just returned from a couple of months at sea so I'm a bit out of date with forum business. I'm very much looking forward to getting back on the Seiran when I eventually make it home next weekend, (if I find the time in between playing with the kids).

Unless I'm missing the obvious I can't tell from the posts whether you have the low or high Rapto. If the low have you found it to seem any less conspicuous on the road than the ICE. Ive never encounted any problems with on road visibility when on a trike but have often wondered whether low two wheelers do so well.
User avatar
[XAP]Bob
Posts: 19793
Joined: 26 Sep 2008, 4:12pm

Re: New 'bent

Post by [XAP]Bob »

I've not encountered any visibility issues - I have encountered people misjudging speed, but then I can understand to an end stent people not expecting me to be doing 40mph..
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
User avatar
[XAP]Bob
Posts: 19793
Joined: 26 Sep 2008, 4:12pm

Re: New 'bent

Post by [XAP]Bob »

Packages in the post today....

A new B&M Lyt for the Rapto, as well as a "Toplight line small" - the whole light fits between the 50mm mounting holes.
And a rear reflector from the same range, a bit wider, but I think it will fit the tailbox - if not then I'll mount it behind the neckrest (somehow)

Also two new hubs - a replacement for the front to take a disc (the fork has the appropriate tabs fortunately) and a disc capable 1.5W dynamo for the rear (£30 from SJS).

The existing hubs are both deore, the new front is an SLX, the rear is an alfine 1.5W dynamo - both take centrelock discs, but that should be fine. I do like the idea of pulling on a brake that actually slows me down properly (the V brakes aren't all that powerful IME)
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
BlackPanther
Posts: 210
Joined: 3 Jan 2012, 11:24am
Location: Doncaster

Re: New 'bent

Post by BlackPanther »

[XAP]Bob wrote:The trike stays - the rapto is currently a fair weather vehicle..

I can't imagine the rapto competing for fun in the snow for instance...

Glad to hear someone (else) thinks it's funny :)


IMHO, low racers have a much steeper learning curve than mid/high racers. I had to 'force' myself to use the Rapto every day for commuting, as the Trice was very much the easy option. Now I've been using it for a couple of months, and with 1,000+ miles under my belt, I feel very confident on the Rapto. She's almost 10 mins faster than the Trice on my 12 mile commute, and it's safe to say that the trike is now my nasty weather commuter. The main probs with the Rapto for me are trying to avoid front wheel spin setting off in the damp, and the chain coming off when reversing the bike (got used to this now though, hasn't happened for weeks.)
This weekend I'm going to raise the seat angle slightly by adding a rubber mount to the bracket. It's just a fraction off being perfect in the neck comfort department. Also hope to get a more comfortable ride through the added 'suspension'. Doncaster roads are pretty poor.
It's amazing just how fast the Rapto will go on the flat when you really push it. No danger of spinning put on the 70 tooth chain ring, but on the 60 toother, I can almost hit 40!
The photobucket images don't work !!!
User avatar
[XAP]Bob
Posts: 19793
Joined: 26 Sep 2008, 4:12pm

Re: New 'bent

Post by [XAP]Bob »

The low racer had a bit of a learning curve, but I'm happy on it now.

I don't think it's much less visible - I've had a couple of silly overtakes, but more cases of people pulling out in front of me - not realising that I'm doing 40+mph...

Just installed lights, I will have to wire them up and either lace up the dynamo or pop a 9V battery in the tailbox ;) (maybe with a 6V regulator)
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
User avatar
[XAP]Bob
Posts: 19793
Joined: 26 Sep 2008, 4:12pm

Re: New 'bent

Post by [XAP]Bob »

Hmm... Thinking about a couple of things...

What generates the pedal steer on a rapto?
Is it the size of sprocket or the closeness to the fork arm?

I'm thinking whether an igh up front might not be a bad idea - but the dedangler wins for the moment ;)


The other thought is that since I have the under tiller brake levers, I'm thinking about a rapidfire shifter for the left hand to use, rather than the twist grip on the right hand. It would keep the arrowhead very clean and tidy, and make all the cable routes easy, then I stop with the right hand and downshift on the left at the same time...
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
Brucey
Posts: 44521
Joined: 4 Jan 2012, 6:25pm

Re: New 'bent

Post by Brucey »

[XAP]Bob wrote:Hmm... Thinking about a couple of things...

What generates the pedal steer on a rapto?
Is it the size of sprocket or the closeness to the fork arm?

I'm thinking whether an igh up front might not be a bad idea - but the dedangler wins for the moment ;)....


Hi Bob,
I've not mentioned this here before but I've just 'finished' (enough to ride it, if not ride it in comfort because the seat is a lash-up) my own high racer. The riding position is similar to a raptobike but the saddle is pretty much as high as on a standard bike, i.e. about 8-10" higher than on a raptobike.

My machine has derailleur rear wheel drive and an IGH mid-drive, pretty much where a pulley would be. The chain runs are both straight and both aligned with one another; there is room for this because of the high riding position, even with 700C wheels.

The pedal steer on your front drive machine comes from two things;

1) the sprocket size (the tension run is no longer parallel to the steering axis in side view except in one gear) and

2) the lateral chainline ( the tension run is no longer parallel to the steering axis in end-on view except in one gear).

Both factors produce a net torque on the steering when you increase chain tension, except in one 'magic' gear. In this magic gear the tension run and the steering axis lie in the same plane; in the other gears there is no single plane that can contain both.

I'm told that you get used to it (not sure how because it varies in magnitude and direction with gear ratio...) but I decided to avoid the issue by using boring old rear wheel drive for my machine.

In some fully-faired front drive HPVs both sources of pedal steer are largely avoided by installing a high level mid-drive with the derailleur/cassette on it. This leaves a simple drive chain (often on the left) which always has the same alignment to the steering axis except when the steering is off-centre; then pedalling gives a stronger than normal centring force (in either direction), and that is all. This setup doesn't work well with large wheels because the mid-drive is pretty much on the rider's eyeline.

BTW this may sound a bit mad but if you could reassemble the cassette so that the small sprockets were to the left of the larger ones, and then get a rear mech to work this back-to-front cassette, I think you can come much closer to having the tension run of the chain and the steering axis in the same plane in all gears.... food for thought? :shock: :shock:

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
User avatar
[XAP]Bob
Posts: 19793
Joined: 26 Sep 2008, 4:12pm

Re: New 'bent

Post by [XAP]Bob »

The dedangler parallelogram would need some interesting work....

The pedal steer is fine, it's really slight, I was wondering about hubs, and they have a sane sprocket, but in an outboard position. I hadn't gone through the permutations work out whe steering torque in my head yet.


It would look "interesting", and the lockring could be an issue.

Fun though.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
Brucey
Posts: 44521
Joined: 4 Jan 2012, 6:25pm

Re: New 'bent

Post by Brucey »

I think that you could perhaps mount a rear mech facing outwards instead of inwards, on a revised bracket, and then reverse the tension spring/pulley mountings to the other side of the parallelogram. Possibly this would work best with a single pivot slant parallelogram mech, with a plain bore for the lower pivot, or perhaps a mech where the lower knuckle can be removed, reversed, and refitted.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
User avatar
[XAP]Bob
Posts: 19793
Joined: 26 Sep 2008, 4:12pm

Re: New 'bent

Post by [XAP]Bob »

Having put in a few more miles (most of my commuting is now on the rapto) I'm not going to go IGH for a while (I might get one at some point in the distant future, but I fettled the dedangler yesterday and it's alot nice having nice crisp gear changes. The pedal steer is small, but I can't go no hands due to a slight instability in the steering anyway (small enough that if I 'carve' down the road by leaning my head left and right it's OK, but it won't go straight without a significant wobble developing).

If I *do* decide on an IGH then I'll look at adding the tensioner at the return idler, not the hub. Although it might need a snub at the hub anyway :(

I'm still looking out for a trigger shifter, but only idle looking.

I tried dropping the seat a notch yesterday, but the tailbox doesn't clear the rear wheel if I do that - grump.
I'm wondering about trying to borrow a 24" wheel (or get one from a skip) to see what the effect would be at the rear. It would already tilt me back further, and line up the rear light better, but it would also change the steering angle by some margin.
But the dynamo would thank me...

The alternative is to decouple the tailbox and the seat - putting the tailbox on 'legs' from the mudguard and brake mounts.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
User avatar
[XAP]Bob
Posts: 19793
Joined: 26 Sep 2008, 4:12pm

Re: New 'bent

Post by [XAP]Bob »

Now done a 67 mile ride, including a jaunt across the Cotswolds. Shame there were headwinds from about 20 miles in...

I modified the tailbox to hold my drinks bladder (straw emerges behind my right shoulder then loops through the neckrest before resting on my left shoulder when not in use. A white nylon bolt covers the hole when I'm not carrying drinks.

I've also found that the little extra weight causes the seat/tailbox to sag and just rub lightly at the very rear - so I'm looking more carefully at options around changing the angle from the seat and/or decoupling it entirely and giving it legs.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
TastyBreakfast
Posts: 7
Joined: 17 Jun 2015, 9:01am

Re: New 'bent

Post by TastyBreakfast »

Image
Geoff.D
Posts: 1982
Joined: 12 Mar 2010, 9:20pm

Re: New 'bent

Post by Geoff.D »

[XAP]Bob wrote:Hmm... Thinking about a couple of things...
What generates the pedal steer on a rapto?
Is it the size of sprocket or the closeness to the fork arm?


Bob,

I don't know if you recall that we once had a long discussion/exchange as to whether there was any resultant lateral force at the tyre contact patch. You felt not. But I argued that the torque around the vertical axis (due to the offset crank/BBaxle width) would create this. I thought it would be small. On a well-set-up trike it would be indiscernible within the steering geometry and, on a bike, unconscious body movement would compensate.

I'm wondering if the pedal steer is a sympton of this resultant lateral force, and the peculiarities of fwd demand an acclimatisation period for the rider to achieve that state of unconscious compensation, which seems to match your experience. Brucey's explanations of the offset chain line/tensions seem to chime with my own thoughts.

By the way, I met you once at a Draycote ride and then again when I visited you at home to pick your brain about fitting a CS-RF3 rear hub to my ICE. You write that you've had a trip over to the Cotswolds. Should you want to identify a coffee stop out this way and fancy meeting up, drop me a line.
User avatar
[XAP]Bob
Posts: 19793
Joined: 26 Sep 2008, 4:12pm

Re: New 'bent

Post by [XAP]Bob »

Pedal steer is the result of the chain tension not being parallel to the steering axis, imparting torque to the steering.

The 24" wheel idea didn't quite work. The steering goes from being unstable, but self centring, to stable but un-centring :(
I prefer the mild instability to the un-centring steering any day.

I'm going to have to work out a new mounting method. Maybe some mudguard stays will provide enough uplift, I have a couple of hooped examples. If not then it's either bracket or full on legs I imagine.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
Post Reply