distributor and starter

[Greybeard]

If I'm seeing this sketch correctly the nichrome wire/custom resistor is 0.1 Ohms.

I've been testing the nichrome wire that I have.
Using my 34 guage wire about 1mm equates to 0.1 Ohms
Using my 28 guage wire about 5mm equates to 0.1 Ohms

[mikeb]

turns out a few problems with my idea. as BSAreg notes the r-c won't cut it on a starter relay (whereas it will on a small low power relay).  i tested a starter relay (off a GS550) that was in the shed and it draws 3 amps on the primary. so that needs better control than a simple RC. GB i've rescanned an updated pic see below - now uses an extra small relay and a transistor. this bit could be made to be tiny.

i made the circuit and tested it on the bench with an old XS750 starter and a 100A battery. the only nichrome i could find was very thin so I used 4 strands in parallel, about 4cm in length which made about 0.15 Ohm. see the video here:
https://youtu.be/Pqnqqve0vco

if you listen you can hear the motor starts slowly then kicks in. next problem the nichrome glows a hot orange even in that half second. probably don't want that on your bike RD unless its got sprinklers.
So how to electrically dissipate ?600W is a significant problem.
i have some thicker nichrome somewhere but can't yet find it.

RD would it be feasible to rewire the internals of your starter motor to separate the pairs of brushes and power initially only one pair then both? I think that's a better option. Then delay the second pair of brushes using either a timer/relay as above or maybe simpler BSAreg's idea of a 2-stage switch - either of which drives a second starter relay.

[olev]

EBay has cheap 20A DC speed controllers. They use PWM. They're usually about 100 x 50mm and fully adjustable.
I motorised the travel on my mill table using one. Works like a charm.
You could perhaps use one of these to provide the low voltage feed to the starter.
Another alternative to the resistor is a string of diodes in series. Diodes create a voltage drop of about .9volt. I'm not sure how much heat they put out or how they handle current.
cheers

[Greybeard]

It seems RD's concern is the force imparted when the ratchet engages. A PWM system could give a slow start but will give full power straight away.

RD, have you considered redesigning the engagement method?

[RDfella]

Firstly, with regards to Neil's suggestion I redesign the engagement method - no chance! I spent many hours designing an engagement method because a sprag clutch - the obvious and easy method - was not possible unless I was prepared to overspeed that by 300%. I reckoned that was too risky and so came up with the present ratchet mechanism. The pawls are spring steel but the rest is mild steel. Of course, it may not work. The gearbox drive mechanism may not work either but if that comes to pass I'm certainly not going to spend any more time designing & machining. I'll just unbolt it and sling it in the bin. For the last three weeks I've done nothing but measure, calculate & machine parts for the starter in my workshop. Remember, too, that this includes a complete re-design of the primary drive outer cover. That in itself has taken a couple of days and is not even halfway there.

There is an old saying: 'everything in my favour is against me' and I'm beginning to live that.
I've posted a pic of the ratchet for Neil to ponder, but the pic below illustrates my frustration. At point A there's a welded-on spacer behind the gearbox to enable the output shaft bearing to recess deeper and keep the bevel gear B as close as possible to the rear. If only. I discovered that this spacer was in the way of the support bolt behind the gearbox, the latter resisting the leverage the chain drive to the crank has on the gearbox. And so the spacer had to go, meaning bevel B is now further away from the rear. That in turn means input shaft C is further forward and consequently there is now no room for the motor driven gear D.
At that point, and because the new rear wheel bearing had arrived at last, I turned my attention to fitting the rear hub complete with newly-attached 49t sprocket. First of all, I cut a bearing seal from two thicknesses of 1/8 gasket cork, given the felt seal was missing and is no longer available. Then I forced the wheel aside (can't get the wheel out without tilting the bike on its side and it's currently strapped to my lift) to fit the sprocket hub. Oh dear. No adjustment because the bigger sprocket fouls the rear chainguard bracket. So next job is to vandalise that bracket. Whilst I figure out how to re-arrange the starter / input shaft connundrum. I'll likely have to order different gears, meaning another three week delay waiting for delivery. Could cut them myself, but frankly - and given my luck recently - I can't be arsed to start making involute cutters and cutting gears.
Maybe I should fit a sidecar and carry a generator and roller starter with me for whenever the bike needs a re-start? Or maybe not. Drove a combination once - that was enough.

[Greybeard]

If I'm reading the ratchet design correctly the pawls will be on the engine side and so when the engine is running the pawls will swing away from the stepped ring by virtue of their counterweight 'tail'. Is that correct?

What about cutting a lot more slots for the pawls to engage with; surely that would at least give less time for the motor to have reached full torque before the pawls bite? In fact, how about a saw-tooth all around round the inner edge of the ring and give the pawls matching serrations. The current large cut-outs are a possible weakness of the ring. A saw-tooth design could be shallower.

Getting an accurate number of notches around the ring could be a worry. Is that something a dividing head could be used for?
If one were hand cutting the notches and the final ones did not quit meet accurately with the start it shouldn't really matter if they were cut back so the pawl missed that area; after all, there are three pawls so one bridging a small gap should not matter.

[RDfella]

"If I'm reading the ratchet design correctly the pawls will be on the engine side and so when the engine is running the pawls will swing away from the stepped ring by virtue of their counterweight 'tail'. Is that correct?"  Spot on, Neil.
You're right also in that more notches would cut down the 'lash' before engagement, but even doubling the number would still leave appreciable slack depending on where in relation to the engagement the motor stopped. I had originally toyed with the idea of using an internal gear with alternate teeth removed (bit like the saw-tooth you mentioned) but, like everything else in engineering, a compromise must be made. In this case, mindful of the fact it takes 3bhp to turn this motor over to start it, I opted for strength. Hence the relatively deep notches. More notches would mean less depth of engagement and less strength.  I look at it as a reasonable compromise. Also, one can't afford to have a pawl not engaging, as that would cause a possibly destructive side-loading whilst potentially overloading the remaining pawls / pivots. This isn't a Briggs & Stratton lawnmower! A sprag bearing would be the ideal answer, but sadly the size I would need have an over-running speed limit of under 3,000rpm. This engine revs happily to 7,000 and should be safe to 9,000.
But who knows? The ratchet may fail, the gearbox might destruct, the reduction I've chosen could be way out or it simply might not turn the engine over sufficiently to start. As things are I'm now facing a 3 week delay whilst another driven spur gear arrives as a result of having to move the output shaft bevel gear. Last week I decided to machine the output shaft chain sprocket I'd received a couple of weeks ago (I'm mounting that by threading it to the shaft rather than a key and grubscrew). Put in in the lathe to open out the pilot bore and promptly blunted the drill. The sprocket was hard. What the hell is the use of a pilot-bored gear / sprocket if it can't be machined? Tried annealing it without success, so I'm now waithing on another one of those.
When I first sketched out this starter I never foresaw this much hassle. But then after wasting months trying to sort Mikunis before finally giving up and changing to Amals, maybe I should have known......

[Greybeard]

Not missing completely, just bridging a small gap. If the job could be done accurately there would not be a gap. I've never used a dividing head but I think I know what they do.

The snotche's don't have to be small. I was just thinking about reducing the distance for the pawl to travel before it engages.

[chaterlea25]

Hi RD,
A worry I have about your design is that when the engine is stopping the panels will re engage and try to drive the starter??

John