Designing your own trigger wheel

[anonymous.shyster]

I've had to design my own trigger wheel as I wasn't able to easily and cost effectively adapt any of the premade ones out there. Here is what I came up with (see attached).

Question is, I'm a bit concerned regarding the tooth design. I got the idea to design them like this from the bottom of this page: http://www.megamanual.com/ms2/36-1.htm However, I've never seen anybody using this design on their trigger wheels and I was wondering if there was a reason for this? Thought I'd ask to make sure before I get it cut.

Thanks.

[Mk1rocco]

This doesn't really answer your question but, Electromotive used to make a "sawtooth" trigger wheel similar to the one you've designed, they're since changed to a square tooth design, I don't know why the change.

[24c]

FWIW, your question is easily answered for me, I have had four versions of laser cut trigger wheels done for a bespoke application, and after the fourth attempt, I get no sync errors from 40-8000 rpm, yet all versions previously I got them intermittently.

I managed to get perfect results with this 36-1 tooth wheel with 5 deg of tooth to 5 degrees of non tooth. I tried other ratios, with a 12 tooth wheel, 10 deg vs 20, and 5 deg vs 25, and a couple of different thicknesses.

36-1wheel.jpg (27.45 KiB) Viewed 1920 times

[anonymous.shyster]

Thanks. I think it's best I stick with the square tooth cut then.

[anonymous.shyster]

Quick question, what's better? Should I design my wheel so that the teeth are as close as possible to the diameter of the VR magnet (4.5mm)? If I do this, the gap between the teeth looks to be almost twice that! Is this okay? Or should I make the teeth a bit bigger?

[anonymous.shyster]

I ask because of all the wheels I've seen, they all seems to have the tooth about the same width as the valley between the teeth. I guess mine is just larger than most others.

**edit** Here is what it would look like. Suitable? Or could I do better?

[dontz125]

The gap between the teeth is almost irrelevant; a 12-tooth wheel has gaps 3x that of a 36-tooth wheel, for a similarly sized sensor. You want the tooth width to be pretty close to the width of the VR sensor, to give you a good sharp REPEATABLE zero-crossing. Too-wide causes all sorts and kinds of problems, as the zero-crossing signal can happen in a continuously variable and unpredictable manner, with obvious issues for timing. Too-skinny also has issues.

[anonymous.shyster]

Okay, I've made the teeth in that one 0.2 mm wider than the sensor. I thought it would be safer than having it narrower... maybe.
So, I suppose this design should be okay to get cut? Any suggestions for improvements before I give them the ok?

[Matt Cramer]

It depends on the size of the sensor. We used a sawtooth design on our 4" trigger wheel but a 50/50 square tooth design on the others. The reason for the sawtooth design was that we wanted to make sure the gaps were as big as the sensor core diameter on a VR sensor. We've found that Hall sensors work best with a square tooth however.

[anonymous.shyster]

I can see why someone who produces these would pick the square tooth design then. It's best to have one or two designs to suit as many people as possible. The sawtooth design wouldn't work for people who wanted to aim the sensor perpendicular to the face of the wheel, or for people using the Hall sensor it seems. However, since I'm only making this for myself, and am aiming for the edge of the wheel with a VR sensor (4.5 mm tip, btw) perhaps it will be good? I may just go the square tooth design to keep safe, unless somebody can tell me that it will be better.