Problems with Optical Pickup - RC Groups
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Dec 07, 2007, 04:29 AM
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Xptical's Avatar
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Problems with Optical Pickup


I have finally got my ET MicroPower working again.

However, the optical pickup does not seem to work.

I have the white TREX main gear installed. Half has been colored with black sharpie. The sensor was placed 3mm from the gear.

Any ideas?
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Dec 07, 2007, 11:29 PM
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Xptical's Avatar
Come on, guys. I know someone knows something.

Tonight, I connected my ET to the PC in live mode. I put masking tape on a drill bit and painted half of it black. I spun the drill and held the sensor in every position at every distance.

The dashboard reported 0 rpm.

Any ideas?
Dec 14, 2007, 01:38 PM
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pinolefm1's Avatar
hmmmm....I believe some tachs need strong backlight to work and might not work with simple contrast markings.I have one of those sensors coming and had thought to put it out on the boom somewhere pointing up through the blades arc.No need to calc gear ratios for head speed then.
Good Luck
Steve
Dec 14, 2007, 08:58 PM
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The manual says you need a solid disk for it to work. It comes with its own internal light and pickup.

The instructions say to put masking tape around the motor and then color half of it black. The pickup is 3~5mm away from the spinning motor.

Still, the dashboard reads "0" RPM.
Dec 14, 2007, 09:16 PM
billpa's Avatar
Hi Xptical,

Sorry for the delayed reply.

I think the problem may be that the sharpie mark is shiny. If this is the case, could you try dull electrical tape, or flat black paint, or other similar non-reflective black?

Regards,

Bill, for Eagle Tree
Dec 14, 2007, 10:05 PM
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Bill,

Does it matter how the pickup is placed? It has two parallel slits in the head. Should they be placed like this "||" or, like this "="? Assuming the motor is spinning like this "->".

Or, does it even matter?

Will testing under fluorescent lights cause a problem?


I'll see about some paint and try again later. Does it matter if the white portion is shiny?
Dec 15, 2007, 01:54 PM
billpa's Avatar
Hi Xptical,

I don't believe the slit orientations will matter. One is producing IR, and the other is receiving it, so both should be fully positioned over the spinning object.

I have not heard reports of fluorescent issues, but I do remember being able to "measure" fluoresent flicker with the optical. But if you are getting no readings at all, something else is wrong.

The white portion should be relatively shiny and the dark portion not. The goal is to have alternate reflective and non-reflective surfaces.

Regards,

Bill, for Eagle Tree
Dec 15, 2007, 10:00 PM
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Thanks, Bill.

I mostly have it working now. I had to paint the can gloss white and then add a flat-black portion to it.

I guess the masking tape was not reflective enough in the "light" area.
Feb 27, 2008, 04:51 PM
Registered User
Bill,

I am having the same problem as Xptical, where he initially used a drill bit I have a motor shaft with a Diameter of ~ 1/8 inch. 1/2 white (bright) and 1/2 black (flat). RPM ~2000. Reading Zero (V3).

I'm thinking this is too small a geometry for this sensor, the light is emitted in a cone and only partial reflected back due to the shaft curvature.

2-4mm distance works for "flat" targets with good light dark contrast.

I am pretty sure if I increase the diameter of the shaft or if the shaft were square it would work.

Can you help by identifying the part number for the opto emitter/Receiver so the cones of the emitter and detector could be determined or what the cone angles are?

This kind of information that would allow us to design the coupler into our installations as opposed to dramatically change the installations to suit the device.

The attachment is roughly to scale but clearly shows for 16 deg cone angles @ 4mm distance 1/8 inch shaft can not be made to work.


Edit:

I increased the dia of the reflective target with a shaft collar of 11mm and the
RPM came alive. Aluminum is a good reflector for IR.

The attached pic's show what did not work 4.5mm Dia (lower motor) and what did work 11mm (upper motor).

The collar attached to the shaft was 11mm, the black set screw provided the break in the optical path. The reflective coupler looks to be vertical polarized for the emitter and detector, but the RPM worked just fine as I rotated the coupler. It did drop to zero when I illuminated it with my incandescent 60Watt work light from about 2 feet. At the 11 mm diameter the coupler was not to fussy how close or far it needed to be.
Last edited by al_wa; Feb 27, 2008 at 07:47 PM.
Feb 02, 2009, 04:23 PM
Registered User
Quote:
Originally Posted by Xptical
The manual says you need a solid disk for it to work. It comes with its own internal light and pickup.

The instructions say to put masking tape around the motor and then color half of it black. The pickup is 3~5mm away from the spinning motor.

Still, the dashboard reads "0" RPM.
Hey gang, hope you don't mind if I dredge this up. The instructions don't mention masking tape. Does it work well? Here's what it says:
Quote:
The surface to which the sensor is pointing should have alternating light and dark areas. The dark area must NOT be shiny or reflective. It should be flat. For best results, half (180 degrees) of the surface should be light, and half should be dark. If you are mounting the sensor near a spinning hub that is constructed light colored material , a black magic marker (if the result is not shiny), flat black paint, or flat black electrical tape can be used to color half of the circumference black. Or, if you are mounting it next to dark colored spinning object (such as black plastic), you can use white paint, white tape, or a white paint pen to make half of the circumference white. Note that if you are mounting on a black plastic spinning object, make sure that the
plastic is flat. It may be necessary to lightly sand it to take off any glossy surface. See Figure 3.
I have a 2cm diameter disk on my heli drive shaft made of dullish aluminum. It's got lots of scratches (milling marks) that make it less reflective than it might be, but it's light colored and I've assumed it's good enough for the light side.

It's the dark side that puzzles me. Any marker I've tried is way too shiny. I tried some black craft/poster paint and it was perfect, totally flat - and flaked off the metal immediately. I've considered electrical tape; glossy but sanding it flat seems to work well. What worries me is creating vibration, always a fear with a big fuel heli. I've been looking around for some light tape to balance it out a bit.

Suggestions? Will the bare metal most likely work? Also, how wide does the prepared surface have to be? If it's down around 5mm or so the weight of tape might not be a big issue. Or, I was planning to go by a larger hardware store and see about some nice, shiny, white or yellow electrical tape. Thoughts?

It'll be a great device if it'll work. I'm coming over from electrics (where Eagle Tree has been a huge help!), and I don't have anybody to take the critical tach readings when I maiden this new bird. But with the lcd screen mounted, I'm hoping I can at least trot up and see the max and average.

Thanks,

misfire

[edit:] Well, the scuffed-up tape seems to work great, 1/2 cm wide, with the bare metal on the other side. However, this is just based on pulls on the rope with the spark plug out. Haven't started the engine yet. But on each pull, I get a reading of 1500-1899 rpm, 250 or so head speed.

I maybe should have cleaned the metal a bit before applying the elec. tape; it didn't stick all that well at first. I may still redo it. Might have been a little oil or something.

Well, I'd still like to compare notes with somebody on this?
Last edited by misfire; Feb 05, 2009 at 04:53 AM.
Nov 27, 2017, 07:50 PM
Registered User
Try Stove Black.

Thanks for the memories


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