Hello Everyone.

Im converting a Webra 120 from glow to gas.

Im utilizing a 1/4x32 spark plug and a NGH 9cc cdi ignition.

Where Im having trouble is how to attach the magnet to the prop hub of the engine.

Ive seen in some threads how a small drill is made and a circular magnet is attached, anyhow on this engine the prop hub has very thin borders so it would not be able to make a drill.

Could I attach a magnet in the midle of the prop hub with JB Weld?

In advance thanks a lot for your help.

That engine will be tricky. I would suggest making a new prop driver that is more solid without the deep groove in it, so you have a place for the magnet. Another method would be to make a two piece slip ring that fits into the groove of the prop driver so you have a place for the magnet, plus you can use set screws to lock the slip ring in place when you have it set. The slip ring would be made in two pieces so you can put it on and into the groove of the prop driver. You would have two screws holding it together.

Now then you could simply build up a dam or barrier and glue the magnet into place using J&B weld epoxy. You need to make a equivalent glob opposite the magnet to help keep it balance of course. One could also simply fill in the groove with epoxy too.

Hi Oddy.
One way is to make a sleeve (tube) that will slip over the prop hub diameter, drill it for both the magnet and a setscrew to make it adjustable. I've done that a few times. Or another way is to make a disc out of 1/16" flat aluminum about 1-1/2" diameter. Drill the center to fit the crankshaft, and another hole farther out towards the outside diameter for the magnet. When you attach the prop, it locks it behind the prop.

John

This disc out of 1/16" flat aluminum is a great idea,

Could you share how you do the hall sensor for this set up

Thank you very much.

VÃ*ctor.

What I do to make a tube type sensor like that is to (very carefully) make a 90 degree bend in the little wires right where they come out of the sensor itself. (Use caution to be sure the correct side of the sensor will end up pointing outward.) I then epoxy the sensor into a 1/4" internal diameter aluminum tube, being very careful also that the wires can't short out on the tubing, and that the correct side of the sensor is flush with the end of the tubing. This tube can then be fastened in various ways to the engine. I often use an "Adell" type clamp which clamps around the tube and has a hole in it that can be used to bolt the clamp to the engine. In the picture above, it looks like he has soldered a little platform to an automotive hose clamp, and used that platform to mount the tube style sensor. This is very similar to how CH Ignitions used to make the sensor mount on their ignitions for use on Ryobi, McCulloch, and Homelite engines.

(I wouldn't trust regular solder to make the clamp; it probably isn't strong enough and would fail. I would use true silver solder, or braze.)

AV8TOR

Sorry, to keep asking, but as you can deduct, electronics are not my specialty.

So, If i solder the three servo extension cables (white, black and red) to an steel plaque or tube and place this inside a rigid plastic or carbon fiber tube to atach with JB Weld to a hose clamp to have the steel tube extreme at 0.5mm from the magnet ....would that work as a hall sensor?

If any pics of an scratchbuilt tube hall sensor, that would be really helpfull

Thank you very much

No, you have to have a Hall Sensor, which is an electronic component and usually comes with the ignition when you buy it.

Sorry, but I am not at home and won't be for a couple more days at least, so I can't post pictures at this time.

AV8TOR

Very interesting thread. Is John still making ignitions? Thanks

Note you also require a small 0.1uF cap mounted right on the terminals of the hall effect. (recommended by manufacturers)
That can get tricky especially for newcomers to electronics.

Make timing rings for the magnet. Install on prop hub. Use set screw for the ring to hold timing position. Easy to set timing any time you want.

I will have 3 brand new engines to test run with new ignitions on them as soon as the weather warms up. One is a Bully 35cc engine, next a 1.50 Saito & last a new Enya 120 R engine. The Enya will be interesting indeed! Best Regards, Capt,n

I just picked up a 30cc Magnum engine that I am going to run on RCEXL ignition, a 1/4" spark plug, and methyl alcohol with 16% oil. That will be interesting too. I have a Walbro WT-499 carb that is made for alcohol that I will probably make an adapter for and use on the engine.

AV8TOR

The Enya 1.20 & the Saito 1.50 I will run on alky I get from Duneland . The Bully 35cc engine has better cooling & has bearings good for using gas. All will use CD ignition.

I want to convert my Magnum .91 four stroke to gas.

It also has a deep groove in the hub so trying to find a ring the right size.
27mm OD on the hub. Was going to try and buy some aluminum tubing and cut a ring and thread a grub screw in it and put a magnet in the ring.

Not sure what grade aluminum to get or what wall thickness?

The grade of the aluminum is not to important. The thickness is just thick enough too install a small magnet & small set screw. Another way is to use the flat aluminum washer back of prop. It would need to be knurled (both sides) so prop would not slip. If you can post a photo of the hub. Capt,n

Here is a neat video....enjoy I did ! Capt,n

https://www.youtube.com/watch?v=BmlEwEx7z4w


Stop video at 20 seconds...he placed the magnet in stock hub !

It would have been better to make a magnet ring to mount to the hub. Then he wouldn't have had to mount the sensor at an angle to get it close enough to the magnet. But hey, it works and they sure seem happy!

AV8TOR

That "V" groove commonly seen in prop hub drive washers is generally there for looks or weight reduction, and in some cases was meant to allow starting with a starter belt as is done with many boat engines. You can turn down the drive hub with a lathe, down to the diameter of the lowest part of the hub. (The bottom of that "V".) Then make a magnet hub/sleeve with the same i.d. to fit there, and with an o.d. the same size as the original drive hub; which is the same size as the front snout of the engine. Then the magnet will be at the same height of the front bearing snout of the engine, and either the hose clamp style CH Ignitions sensor mount, or the plastic sensor mount commonly supplied with RCEXL ignitions, will fit perfectly.

AV8TOR

av8tor Check your P mail

I wrote you back yesterday Captain John. What a bummer that happened.

AV8TOR

Thanks AV8TOR.

Only problem I have there is I don't have a lathe. Or know anyone who does

Have been thinking about the washer setup. With an alloy disc behind the prop.
But I keep having thoughts of the prop coming loose.

I guess if I mark the faces of the washer to allow the prop and hub to bite on something.

I have the .91 ASP FS pulled down waiting on new bearings to arrive and I just noticed the cylinder sleeve will fit over the prop hub. It's not a tight fit. But its close enough for a grub screw to be used to attach the ring.

I wonder if I cut one down to size. Drill a hole for the magnet undersize. Then heat the ring and insert the magnet and let it cool down.
That way it should grab the magnet without the need for an adhesive. As the ring will shrink back when cool and close the hole?

The cylinder for these engines is like $6.50.

I have the FS61AR as well. The sleeve and hub don't quite fit. I reckon if I heated it up to do the magnet install I could get it fitted. They measure the same on my cheap vernier's. But they dont quite fit into each other.

Cut that sleeve to the correct width so as to have enough material to drill for the magnet. The hole for the magnet can be a tad larger & use JB Weld to hold the magnet in place. The sleeve would need to have no steel in it. Have some person that has a lathe make a timing ring out of aluminum. Real easy to do. Good Luck.... Capt,n

A. You don't want to expose magnets to heat, it will weaken and/or destroy them.

B. The sleeve for the magnet needs to be of a non-magnetic material. Steel would conduct the magnetism and likely cause triggering problems.

AV8TOR

VeeAte .....check back .....I corrected my post