Tilting tadpole - with thanks to Alan Maurer

If I get this right it will be a tilting Tadpole along the same principle Alan Maurer built his. It will use caster as the steering mechanism in that a heavily castered wheel will steer when tilted. Steering and tilt will be separate functions though in that it'll be able to tilt without any steering but the opposite is not True, ie it can not steer without tilt.
This will be my mk3 as no.1 was a complete failure and scrapped and no.2 was my green one which works fine but on different principles. Progress is somewhat limited in that all I've done so far is to sort the rear end for it. The swing arm came to me as an unknown Whyte unit as part of a deal and languished in my pile for years. It weighs almost nothing which is why I want to use it. On looking for a dropout for it it became identified as a Whyte JW2, made about 20 years ago and attached to a very low volume forkless mountain bike. Even Whyte don't sell the dropout any more - marvellous. On scouring the net for anything similar it appeared a Marin unit may fit and £21 later indeed it did. Quite why Whyte don't say this on their website when Whyte and Marin are under the same company is beyond me. The pivot on this is a pair of real actual bearings - a first for me. The bearings in the arm were of course seized so I pulled them out with the time honoured trick of a bolt and socket. It turns out they are imperial which surprised me given I believe they were made in the UK. By a stroke of good luck I had several such bearings I'd been hoarding for years on the off chance I'd ever need them so pressed them in. This is why you never throw anything away. A mount to the chassis would be needed and I've used some 1" 16swg tube as a bearing holder with some 3/4" tube in the middle to seat another pair of the same bearings against and a pair of oilite flanged bushes at the outer edges to help rotation and protect the swing arm. It all slotted together nicely to make the mount.

The swing arm origin.




Somewhat odd dropout needing bolts to hold it in. I need some longer bolts.



The parts for the chassis mount



And assembled and in place



Sufficient room for a 10 speed freewheel



The brake mount utilised a front 160 to 203 adapter wrong way round and with an extra hole drilled and tapped into it. I have no idea what those holes are originally for in the swing arm. Clearly they are not std disc brake mounts and they are replicated both sides. At a later date I'll kiss the adapter with a flap disc to de-blue it and grind the spare hole off.



The rear brake will be very much needed on this unlike many tadpoles. Applying the front brakes means that the steering mechanism wants to steer further as you brake as the caliper mount has to be attached to the caster arm. This desire to steer further has to be resisted by the rider applying pressure against the bars. Not ideal but pretty much every tilting taddy I've ever seen has some compromise.
It's not much to show for 3 hours work but you have to start somewhere. The chassis will be built from round stainless and I have a stainless reel for the MIG. Yes it'll be a pain to work but most of that work will be done with powered tools such as a chop saw. I'm hoping not to need to paint the bulk of it. Certain parts will need to be painted such as the rear swing arm mount which is mild. I do expect to need to dry it after any rain and oil it regularly. This won't be a daily rider though so such demands can be accommodated for the sparkle provided. If it does start to rust I can always paint it later.
Next job will be attaching the main beam to the swing arm. I have a 1" drill so will see if I can get that through the 45mm tubing to slot that swing arm mount through. I expect that to be my first cursing session against my stainless choice.

 

Been back in the garage since the 1st post and actually got a 1" drill through the 45mm stainless tube! I marked the tube and drilled each side separate as it seemed like the better way to get things square as opposed to drilling straight through. I wasn't wrong either, the hole is dead straight and the pivot assembly fits in very snugly. The main tube is perfectly in line first go - I ought to buy a lottery ticket whilst my luck holds. Still needs welding which should be easy given the perfect fit. It's usual for me to make a large tack at this point and then club and whack it into alignment. It's rather nice not to be doing that.










I was going to go for a mesh seat this time but my usual Polish supplier is now knocking the VAT off for UK sales so I ordered another of the usual ones. The next few days will tell whether I have to pay the VAT at the import side of things. I thought it worth the risk.

 

It'll tilt on M12 rod ends. The rod ends at the end of the crossbeam will screw into M12 long nuts that will be welded to the bit that rotates for the caster steering. The middle pivot will also be M12 rod ends fastened to the end of long(ish) M12 8.8 bolts that come up through the main beam. A M12 bolt will go through the middle rod ends and through a piece of pipe welded to the centre top of the crossbeam. Where Alan uses a sub structure welded to the main beam under the front I won't as my crossbeam will be lower and therefore closer to the main beam. I need to keep 1.5" of clearance between the two main tubes to allow enough swing on the lower one as it tilts. The centre ones will be fine as they only get tension applied through them. The end ones have to hold my weight and I'm hoping M12 will do. The rod ends will be fully into the long nuts to give them every chance.

 

The crossbeam consists of two tubes, one inside the other. The outer is 45mm and the inner 25mm. To the inner on each side is a flanged bearing that sits in the outer, then a thrust bearing so it steers smoothly under load and then 3 split clamps. The clamps are all sigle at the moment but will end up welded together as the long nuts for the rod ends will be welded to them. I had to skim the 25mm tube at the ends to get the bearings on. No big deal, just the flap disc grinder in the vice and rotate the ends against it until correct.







I'll make the uprights next and then attach them to the crossbeam. Having no kingpin makes the uprights a simple matter.

 

The inside tube runs all the way through the outer and the split clamps hold everything in which is why I'm using 3 each side. Should those clamps proove insufficient then I'll either need to pin or weld the clamps though welding means grinding if I ever need the assembly apart to replace a bearing. I do expect the clamps to hold though.

 

More work done on the crossbeam. The caliper mounts are now made and fixed. A failure of planning has lead to the calipers going on top of the discs instead of the side as hindsight now tells me that position is occupied by the M12 rod ends. Not a major issue and I suppose it will highlight the flashy red calipers. My crystal ball did however work for the long nuts welded to the clamps. I fully expected to have to run a tap down them after welding so had already bought one. Oh the joys of tapping stainless - still it was a good workout. I need to add a small arm to each end to act as the steering arm

 

Got the 16mm holes drilled for the crossbeam to main beam mount. A new 16mm drill went through surprisingly easy. It's almost aligned but will need a wiggle with the drill to bring into perfect alignment which won't be any issue once welded in. My seat is down the road at Dewsbury UPS depot so hopefully will be with me Monday

 

Sitting on it wheels now.




A major issue arose. With the planned bolts tying the crossbeam to the main beam there was a lot of lateral movement in the crossbeam - a couple of inches fore and aft at the wheels. I had enough height difference to chop them down and still allow enough tilt. I chopped them down by 40mm from this...




to this.....




...and that has solved the issue. Despite being 8.8 high tensile bolts they simply had too much give in them and that extra length was a lever on the stainless main tube. Lesson for anyone following me - keep the distance between tubes as short as possible. The tubes now touch at a 32 degree lean angle which I expect to be enough. I can always get a bit more lean by winding the rod ends up though again that'll increase flex.

Speaking of flex that weld of the main pivot to the crossbeam will need some reinforcement. On a perfect road it'd be fine but a pothole at one end only will impart enough force on the crossbeam which will act as a lever on that weld to destroy it. Like Alan I'll add the same type of reinforcement there.

You can see the outer wheel leans more than the inner one.




This is a function of the lower arms having two inboard pivot points versus one on the top. The inner wheel is turning a tighter circle so extra lean is useful. The uprights were originally made to a length to support the longer pivot bolts. The main tube now rides higher and the control arms now have a higher mount in the middle than the outside. I was going to shorten the uprights to match but changed my mind.

With the original bolts the arms were parallel with the crossbeam and the inner mount set to match the outer at 22.5 degrees caster which is bang in the middle of the 0 to 45 degree max range for the steering. The control arms have to swing on the outer mount to steer at various levels whilst the inner mount is fixed. This means the effective length changes which in it's original long bolt form means that if you set camber to zero at 22.5 degrees steering you get increasing positive camber as you move from that central point in either direction. Now in short bolt form there's more movement away from the 22.5 setting as you take steering out but less movement away as you add more steering on. This is a better scenario I believe as the smaller geometry changes will occur at more extreme steering where I'll expect to appreciate the smaller movement more. I'll set it at 22.5 degrees with some negative camber with a view to only coming to zero camber as it's at zero caster.

Realistically I need the seat to do much more on it.

 

Still no seat so limited in where I can go 'till it arrives - **** UPS who've tracked it to Dewsbury (3 miles away), lost it and then found it back in Poland!

Bracing added to cross tube.

 

I've found a fundamental issue in my design. The front wheel axle is above the pivot for the wheel meaning I'm lifting the front as I add steering. Given my own generous proportions it means I have to lift a lot of weight to add steering. The axle needs to be, ideally, level with the pivot which creates some design requirements to avoid one bolt passing through another at right angles. Not quite a schoolboy error but I should have seen it sooner. Time for some redesigning and reworking.

 

My 16mm drill has again died in service so I await another to do the other side. It's added 38mm to the width which I could reclaim by cutting the two main crossbeams down but probably won't. I was going to move the lower mount inwards by 19mm, the same as the top mount has moved but thought better of it. A difference is needed between the top and the lower pivots with the lower arms combined being less than the distance between the top pivots. The reason is to make the inner wheel lean more. It leaned a bit too much more IMO so this change will half that extra lean on the inner. I expect that'll mean it's now slightly worse off at lower speed and better off at high but the proof of that will be evident later. My Polish seat has STILL not arrived with UPS taking 6 weeks to move it from Poland to the south of England so far. I have a mesh seat if all else fails but really wanted the Rocek one. The bars on this will need to be high enough for the seat and some portion of my thighs to slide under as I tilt and with this one having me nearer the front axle than Alan's I suspect my bar mounts will need to raise up before going backwards. I can get a fibreglass seat lower which will help here - another reason for wanting the originally planned seat.

One side fixed. I'll swap the current nylock for an aerotight so I can tack it in place with no plastic to melt.

 

The main frame rail has been "Z"ed to get the seat lower. The cross beam has to be level or tilt and turn get unacceptably combined so I couldn't just notch the frame. The seat is mounted nice and low now which is essential to the tilting effort. The rider now tilts roughly around their centre of mass and as such doesn't move too much left or right. This means the bar mounts can be that much closer to the rider. Bar mounts and bars are next along with the steering arms. It's going to feel weird either pushing or pulling both bars at the the same time instead of one pushed and one pulled.

 

Bars now in. The pictures show various amounts of input and the resultant steering. Nothing is overly tight so true positions are not going to be seen but it shows the general idea. I need to angle the BB further up so when it tilts my foot still clears the floor. That will leave it somewhat higher than usual when upright. Can't be helped.

 

I've taken the decision to electrify this from the start so I'll need to brace the rear dropouts. I want a rear wheel motor on this rather than a Bottom Bracket drive to keep some drive if the chain snaps and will probably prevent that happening anyway. The dropouts are aluminium and simply won't take the grunt of resisting the axle twisting and if I ruin this swingarm my chances of finding an identical one are slim given it's heritage. Here's the plan. I have some 32mm washers which fit into the recess nicely. I need to weld several together for thickness, cut a slot for the axle then make a bit to brace to the two holes above. I need one each side and the right hand one also needs to be tapped for the dropout as that area needs to be flat so no M4 nuts poking up. The next few days will see if reality meets plan.

 

Here's the extra steel bracing the dropouts which runs around to the two M6 bolts above plus a lugged flatted washer welded to a bit of steel around one of the M6 bolts. It means the wheel can't be taken off without undoing one of these M6 bolts each side but given I'm running a Schwalbe Marathon the chances of needing to do this at the roadside are small. There's 5mm of steel this side and 3mm on the other. There's less there because the dropout wants some room too.




Almost done now bar the cable and wire management to tack on plus the cabling and wiring themselves. The V brake bosses made excellent places to brace the rear carrier rack. There's three 116 link chains there and I'm still short by 8 or 10 links. I do have a 10 speed with a very wide range of gears and a 52T on the front so I'm figuring that is why 3 chains have come up short. I've ordered another one which is a bit of a shock to the wallet as the existing three came from Ali Express but the extra is coming from Amazon as I don't want to wait a month. I actually ordered silver from Ali Express and the numpty sent me gold. Given the shiny gold coloured ones are more expensive by some margin I chose not to complain.
One thing I'd like to have done differently is the calipers are on with the actuating arms at the front. ie the cable comes in from the rear. It looks like it'd have been better to have done that the other way round and loop the cables in from the front. I can't simply swap them without remaking the mounts so will try cabling it up as is first and see if it's acceptable. It'll be nice not to have to rip it apart once built with it being stainless. It's crippled many a drill bit but I think it was worth it.