Now Seal starter motor

[gadabout]

Jason ,
Thanks for this, how do you arrive at the said dimensions?
I have cut a 144 tooth gear ( used 144 as it is 2.5 degrees each tooth so I could see what was happening easier) this afternoon using the wizard in Mach3 , had to edit the file a lot as the code it spat out was weird  in places , but it ended up cutting a nice ( to me) useable gear using the straight flank ground tool bit as a single point cutter
Cheers
Mark

[Jasonb]

There is a table that goes with the drawing that Jo published giving the diameter of the buttons, their spacing and position relative to the end of the cutter. for 1DP You then divide the numbers in the chart by the DP to arrive at the sizes in my sketch.

It would also be possible to use the FMGear addon in fusion to draw the actual gear and then use the profile of one tooth to get the shape of the cutter.

As has been said the 135 to rack profile is not far off being straight and with the flank of the gear tooth only being about 1.5mm long and 10mm radius a straight cutter would probably do for light duty use. I've added a vertical line to show the edge of the 1/16" wide cutter as the rest won't be cutting and you can see if scaled down to actual size it's a very small arc.

[gadabout]

Jason, thanks , I think I am starting to understand it now
The gear I am making is to be a ring gear on the flywheel of my Seal 15 cc so I can have electric start on it . It will be in constant mesh with an idler gear that has a one way bearing fitted.
Thanks
Mark

[Vixen]

................
The gear I am making is to be a ring gear on the flywheel of my Seal 15 cc so I can have electric start on it . It will be in constant mesh with an idler gear that has a one way bearing fitted...........

Mark

Hello Mark,

At last we know what you are thinking of making.. a starter ring for the Seal.

Are you sure a 64 DP gear will be adequate for starting your engine. The 64 DP tooth form is very fine, it may be  more suited to an instrument than a starter ring. Have you considered using a starter motor with a built in reduction gearbox (like the guts of a cordless drill), which would then allow you to use bigger/stronger teeth form on the starter ring?

Cheers

Mike   

[Jasonb]

I'm inclined to agree with Mike, 64 DP is quite fine (not far off a coarse knurl!)and it would only take a bit of a kick from the engine to mash a tooth unless there was some form of slipper clutch in the drive.

If you went with something around the 70T mark then you could use MOD1 which is a bit more substantial and cutters a lot easier to come by and it would not look too chunky and out of place on a flywheel and be around the same diameter

[Vixen]

Hello Mark

I would be inclined to go even courser and would consider using MOD 1.25 with fewer teeth, especially if you have the V8 seal in mind. You then have the problem of matching the starter motor reduction gearing.

Mike   

[Roger B]

My 25cc single has the  'Dynostart' with a 4-1 reduction from an RE 850 motor. The 12 cc twin has a directly coupled RE 800. Both start easily with a 12V battery.

https://www.mfacomodrills.com/motors/motors.html

[Jo]

At the Guildford show (on the odd occasion that an engine did not start by hand ) Mike Coles used a rechargeable battery drill with a soft plastic cone on the prop/nut with great effect... no gears to cut, no horrible whine from a meshing gear being over driven once the engine started 

Jo

[Jasonb]

Sounds similar to the electric starter I use on engines with a prop but with the bonus that most drills have a clutch. Same starter also has a hard rubber ring that fits around the outside of the part that holds the conical rubber insert and that is what I used to us eon the buggy engines, just hold against the knurled edge of the flywheel/clutch carrier and off it goes. This setup actually gears up the motor speed but not a problem as the glow engines are faster running anyway.

Though kind of nice just to press a starter button and have the engine burst into life

[Roger B]

I don't think I could do my fuel injection experiments without electric start. I am already running out of hands 

<a href="https://www.youtube.com/watch?v=tJECoGtBc6c" target="_blank">http://www.youtube.com/watch?v=tJECoGtBc6c</a>

[gadabout]

Hi all,
Thanks everyone for your advice!
The reduction drive unit I have already made using some rc car gears, the big gear I couldn’t find easily so hence cutting one .
Tried the gearboxes from cordless drills etc but looked way out of place and couldn’t find any smaller ones that were good enough.
My Seal will be in a boat so can’t use the cordless drill to start unless I drive it from  the prop shaft .It starts easily by flicking the flywheel so hoping the 64dp gears will be ok, time will tell. Picked that size as I thought it would look more scale size on the flywheel.
I want to place the boat in the water and hit the starter to go!
There is a one way bearing in the gear train.
Cheers
Mark

[Jasonb]

You could do your boat in the same way the Helicopters are started, have a vee grooved flywheel and leave a belt in place. To start just hook the belt into the vee groove on the side of the electric starter/cordless drill and give it a whiz.

Starting in the water will put more load on the starter gear and if thats combined with a small pinion to get the reduction 

<a href="https://www.youtube.com/watch?v=OLNdKKpqvxY" target="_blank">http://www.youtube.com/watch?v=OLNdKKpqvxY</a>

Probably best not to get into bevel gears but the Tiger Drive or something similar would also work with a cordless drill

https://sullivanproducts.com/tiger-drive/

[gadabout]

Jason, I have raced model boats for years and that’s the way we always started them, now I’m older I’m more into semi scale and just want to put it in the water and start it there. The reduction drive works out at 1:24 , all a bit of a guess but hope that it will be all ok. My plan is to start it and warm it up on the stand first . The option to start with cord or belt will still be there.
Cheers
Mark

[Jasonb]

I suppose another advantage of an onboard starter is that if the battery is large enough it may get the boat back to shore if the engine stops

[gadabout]

Jason, yes that was my thought too!
Cheers
Mark