distributor and starter

[RDfella]

Couple (two for the price of one) of queries for the electrical wizards amongst us.
First, distributor advance springs. Am using a Lucas DKX2 distributor on the project (should I call it a special now it's running and registered?). The advance has two springs, both .730" measured inside the loops with 9 coils and wire thickness of .029". Measuring the advance curve using a strobe and the machine's rev counter, I got half advance around 1700rpm and full a shade under 3,000. I'd like to get the advance in sooner, especially the first half. So does anyone remember the 60's car distributors which had a light and a strong spring - where the lighter was in tension at rest but the stronger one slack, to pick up its load later? More to the point, where I might get some?

Secondly, am slowly progressing with the starter design, mainly held up waiting for parts like bearings etc. But my main concern is that as I'm using a ratchet instead of a spragg clutch, it may engage with a bang that could be destructive. Now some diesel engines have a clever design of starter whereby only two field coils are energised until the bendix is fully engaged, whereupon the other two are connected and the full 1,000A does its job. No room on the diminutive motorcycle starters for that, I'm afraid, but would like nevertheless to create a 'soft start'. I'm thinking of maybe having a separate button that supplies, say, 3 or 4 volts to the starter to engage with the engine, after which I'd hit the usual start button. I'm using a Firestorm starter (known to start a short-stroke 1,000cc high-compression bike) together with a 200A CCA 12V battery. Could I achieve what I want with a resistance and, if so, what Ohms would be suitable?

Thanks in advance for any assistance,

[chaterlea25]

Hi RD,
I can only recommend you contact the distributor doctor to ask about the springs,, http://www.distributordoctor.com/

As to your starter issues,  here is a random thought.. I do not know if the starter has a pre engaged or inertia gear??
Now pre engaged solenoids usually have two coils built in, one is in series with the starter winding so it is "bypassed" once the starter is fully engaged , the second coil holds the engagement in place
 in other words the starter does not spin until the gears are engaged

John

[Greybeard]

Ref the starter question. Digital controllers are the modern method of controlling a motor.
This explains the method better than I can:
https://en.m.wikipedia.org/wiki/Electronic_speed_control

I've been playing with Arduino processors over the last few months. They are very small so easy to house on a bike. On your machine I'm wondering about using one of these devices to send a signal to a digital motor controller. The effect should be an immediate engagement of the drive followed by a steady rise in speed.

[bsa-bill]

Tell me you once had a Spectrum GB

[Greybeard]

Tell me you once had a Spectrum GB

Amiga

[Greybeard]

This sketch shows how it works. The (full) current is applied in pulses that can be lengthened or shortened

[RDfella]

Thanks for the input, folks.
Re the starter - I'm familiar with reduced-power on starters before engagement, as on diesel motors where usually only two field coils are energised with the remaining two making contact once the pinion is fully home. Unfortunately there is no room to modify a motorcycle starter motor thus. BTW, the starter motor will be fully engaged at all times, the only engine engagement / disengagement being the ratchet mechanism on the crank, the life of which which I'm hoping to prolong by a soft start.
The use of a speed controller is interesting - have them on my model boats - but an overkill regarding what I'm looking for. I just need a second or two of reduced power to soften the ratchet engagement. As I don't have a bendix engagement, it won't be feasible to incorporate that in the motor, even if that were physically possible. I was presuming a separate circuit (eg incorporating a resistance) to supply reduced volatage which could be manually activated before hitting the start button proper.

Re the distributor, I contacted the distributor doctor, but his solution was to send him the distributor and he'd rebuild it to whatever advance curve I wanted. Sounded a bit long-winded and potentially not cheap. All I want is some springs. Failing that, I'll make some.

[chaterlea25]

Hi RD
How is the ratchet gear engaged / disengaged?
Could it be done with a solenoid that could be powered then after short time delay the starter motor is powered
Any resistance would need to be rated in the kilowatt range if connected in series with the starter
If the starter is 4 brush, could it be split into two and two which would reduce the initial "kick" ??

John

[mikeb]

Arduino controlled PWM driving FETs or IJBT’s  is very modern but unnecessary. I once made a 12v motor soft start by adding an in-series relay with a time delay switching past a low value resistor, so it started for a second at half volts then clicked to full volts. Is that what you mean or have I got the wrong end of this?

If it is… mine was more trivial as 15 amps, but the maths is the same: The resistance is just ohms law V=I*R so 6v (drop) at 200A = 0.03 Ohm. The resistor’s power rating = IxIxR = 200x200x0.03 = 1200W. If the starter motor is 1200 watts then its 0.06 Ohms and 600W. Still sounds brutal but I doubt the current would be that high at 6V or the resistance that low  - use some nicrome heater element wire (off an old bar heater)  and experiment. This wire is often 4 Ohms per metre, or thereabouts. For the ‘switch’ use another starter relay (in series with the first) and ‘time’ it with a resistor (100 Ohm?) in-line with a capacitor (220 microfarad?) that is across this relay. These values are wild guesses as I don’t know the current draw of the relay. If the relay current is super high then drive that with a smaller third relay.  Does that make sense? If so – start with higher resistance values and lower it to see what works.

[RDfella]

damn - posted itself before I'd finished. Ignore, see post below

[RDfella]

John - the ratchet is spring-loaded. It will engage when the starter turns but disengage when the motor starts and the pawls are free (centrifugally overcoming the springs) at 800rpm. What bothers me is the fact that, depending where the motor comes to rest, the ratchet could have 30* of rotation before the pawls engage the notches. As such, it could engage with a hefty kick, possibly damaging the ratchet. What I'd like to do is gently motor the starter over to get pawls into contact first before hitting the start button. Starter is 4 brush and, as you say, feeding two coils initially is a well-oroven way of achieving a soft(er) start. However, space is damned tight in there and I doubt I could physically achieve that. Was thinking more along the lines of a separate button to achieve initial engagement, possibly through a series resistor, which would then be released ready for the starter button to be used.
Damned nuisance I couldn't find a suitable one-way sprag bearing. Would have made life so much easier!

Mikeb - looks like you have the solution, very helpful. With enough time I have been known to work through electronics (eg radar / autopilot problem tracing) but it makes my brain hurt. Not my forte.

[chaterlea25]

Hi RD
For testing purposes you could use a six volt battery that would give 25% of the power of a 12v battery
sequential solenoids with the 6volt engaging for enough time to engage the ratchet then the 12v taking over????

John

[Greybeard]

John idea sounds good to me. Momentarily a small voltage just to get the ratchet to engage then apply full power.

[Greybeard]

I have some nichrome wire. It's quite fine guage. 32 and 28. I'd be happy to send some off to RD but it may be too fine. MikeB, do you have any idea how thick the wire should be?

Mike, that picture is not in focus, do you think you could try again?

[Bsareg]

That diagram doesn't look right to me. Surely the low impedance of the second starter coil will prevent the capacitor from charging via 100 ohm. What about a two position switch, first position energises the main relay, and the second position energises the the resistor cutout. Much like a heat position on a diesel.