Now Seal starter motor

[Roger B]

What is the ratio between the flywheel gear and the driver gear? With a 10-1 ratio and an engine speed of 3000 rpm the driver gear and the one way coupling will be doing 30 000 rpm.

[gadabout]

Roger,
 Thanks for bringing this up, I had not thought of the reverse effect! The gearing to the one way bearing is 7.5 to 1. I doubt if I will ever run it in the boat past 2000rpm so the little bearing will be seeing 15000 rpm! It is a quality bearing from  a rc car clutch so I am hoping that it will be ok , it will not get much running either.
Tell me about the ‘Dynostart’ that you mentioned, is it a commercially available thing? I did look at the link but couldn’t see it.Thanks
Cheers
Mark

[Roger B]

Dynostart is an old tradename (possibly German    ) for a combined starter/generator coupled directly to the engine crankshaft. My 12cc twin has an RE800 motor connected to the flywheel which I use to start the engine and then as a generator for load trials. The direct coupling means that it never sees more than crankshaft speed.

[Bluechip]

Could well  have been  German manufactured.

IIRC it was the Siba Dynastart, fitted to BMW/Isetta, Heinkel, Messerschmidt bubble cars and some scooters.

D.

[Roger B]

I think they were also used on diesel hydraulic locomotives. Diesel electrics could be started via the main generator.

[Allen Smithee]

To avoid the step-down gear running all the time you could install the Sprag bearing between the crankshaft and the ring gear rather than between the pinion and the motor. That way both ring-gear and pinion will only be turning at all when the starter motor is running.

Alternatively you could choose a starter motor with a Kv low enough to turn the engine over without reduction gearing. If you have a reasonable idea of the torques and speeds you're after I may be able to help you with that.

Just thoughts...

AS

[gadabout]

I did toy with the idea of the one way bearing on the ring gear but couldn’t work come up with a satisfactory solution.
I will have a look at moving the one way bearing over one gear to get the ratio down to 2.5-1 so the bearing is slowed down considerably.
 I have no idea of the torque required but think turning the engine over at 300 rpm (cordless drill speeds?) would be adequate . The motor I am presently going to use is a brushed 27t 400 wattage( being the name) motor.
Thanks
Mark

[Allen Smithee]

You're not doing yourself too many favours with that motor choice. The Wattage Cobalt 400/27 is a low-torque, high-revving motor with a Kv of around 2,400rpm/v and a rated max current of 31Amps (this is probably a peak rating for around 10 sec). A 1,000rpm/v motor with similar peak current rating would only need 4:1 gearing at the same voltage, while a 60A-rated  500rpm/v motor on half the voltage could be used direct drive to do the same job.

So assuming that Wattage 400/27 on a 10:1 gearbox is suitable you do have lots of other choices.

AS

[Allen Smithee]

I did toy with the idea of the one way bearing on the ring gear but couldn’t work come up with a satisfactory solution.

I think the image in my mind was to move the starter gear off the flywheel - to have an extension shaft to the starter with the sprag in the shaft. I'm not familiar with this engine so I have no idea how practicable that would be!

AS

[gadabout]

AS,
Thanks for the reply.
The final gearing is 24-1 (just a little under). I bought that motor as it was recommended as suitable by the local hobby shop, I have no idea about electric motors  I was trying to buy as small a motor as I could and the one I bought was bigger than I wanted. Running on an esc at 6 volts atm.
Regards
Mark

[Allen Smithee]

I don't think I'd use an ESC - just a relay. The ESC won't like the high start-up torque demand and would probably go into over-current cut-off. I know FEMA make a lot of on-board starter systems for aircraft and boats from 6.5 to 60cc. Their setup for a 15-20cc 4 stroke generally uses a Graupner speed600-size motor (36mm dia) which is around 1,900rpm/v used on 12v. They use a 2-stage reduction drive with the motor and 1st-stage gear mounted at the opposite end of the engine to the flywheel which drives a separately-mounted pinion on the flywheel ring gear via a semi-floating cardan shaft (one end splines, the other with a UJ). The cardan shaft incorporates a sprag bearing at the flywheel end. This setup would be easy to copy, perhaps using two 5:1 gear stages.

For reference the FEMA systems are detailed in this brochure:

http://www.fema-modelltechnik.de/Neue_Dateien/Katalog_S3-14_eng.pdf

AS

[gadabout]

AS,
 Thanks for that link, most interesting! Might have to do a complete redesign by the look of it.
I want to be able to start it from the transmitter so I don’t know how to use a relay to do that.
I am so far into the current setup that I might just persevere with it and see how it goes then redo it properly .
Regards
Mark

[Allen Smithee]

The easiest way is an "RC Switch" which is essentially a relay (sometimes a solid-state relay) that plugs into a servo channel and is switched on or off by that channel. This is a basic 1Amp one made by Mike Ridley (in Southampton):

https://modelradioworkshop.co.uk/shop/power-switching-devices/single-relay-controller-switch/



If you contact him he'd probably knock you up a 40A one for a few extra pennies (he's a very helpful chap), or you could use that relay to switch a bigger one on and off.

There are other options from these cottage industry ones up to mass-produced chinese ones like the Turnigy one (cheaper, solid-state but rarely in stock!):

https://hobbyking.com/en_us/turnigy-receiver-controlled-switch-1.html?wrh_pdp=1&utm_source=google&utm_medium=cpc&utm_campaign=google_gb_shopping&countrycode=GB&gclid=CjwKCAjw87SHBhBiEiwAukSeUWrLxZeL4LDeRa6ysvvOu0E8YkkAnaFxiQrFWgqJQtGSnP2PD_EakxoCxgYQAvD_BwE&gclsrc=aw.ds



I'll have a hunt in my RC bits drawer - I should have a couple of ancient 20-30Amp ones kicking around from the days before ESCs were affordable.

AS

[gadabout]

AS
Thanks again for the links , there is stuff out there I didn’t know existed!!
Thanks again
Mark

[gadabout]

AS,
What motor would you recommend in the 480 size? Shaft size needs to be .125” , don’t want to go bigger in diameter than 28mm .
Thanks
Mark