Bicycle rotor tac how to

ggfirestar

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Have flown lot's of different ultralights 3 different Gyro,s Bensen,Dominator,Air Command
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How do you set up a bicycle speedometer to a rotor tac.
 
Date: September 30, 1999 08:27 AM
Author: Mike Schulman ([email protected])
Subject: $15 (or less) Rotor Tach

I've had several people ask me about this so I decided to post it. This rotor tach is cheap, dependable and accurate. There are several places that you can get this tach. I got mine at Wal-Mart but you can also get it at Target, K-Mart and a lot of bicycle shops. It is the 5 function Cyclocomputer made by ACE Model # 810-230. It is sold under various brands but it is always identified by the Model #. It is powered by a small battery (with auto on-off) The directions are very simple and easy to set. It comes with about 6' of cable and you will need to splice in a longer section - I have lengthened my cable to 10 ' and it still works. You mount the magnet to the prerotator ring or to the rotor head, and then you mount the pickup where the magnet will pass within 1/4" of it. Read the instruction for setting the cyclometer and set it for metric "L" with the number 1667. (If you prefer to use two magnets, space them 180 deg apart and set it with the number 833). Mount the digital readout where it is convenient --and there you have it!! The read out will show a decimal point right before the last digit-just disregard it. The unit is accurate to within five (5) RPM. (BTW this is not my idea Tom Sled told me about it!!)

Mike
 
I've never been able to find the "Ace" brand...or those model numbers.
What I have found is that any of these types of bike meters will work...I got mine on Ebay. YOU MUST pay attention to the Tire diameters that the unit will work with. Some can be set for 0-to whatever diameter (usually in Centimeters)...others only to diameters larger than the pre-rotator disc.
DO NOT BUY THOSE...make sure you get the ones that will allow 0 to whatever (I don't remember exactly how it was worded on the package)
I ended up with three units that could not be programed with the needed small diameter...but they set me back $6- for all...so no big deal.
I was at Wal-Mart three days ago...was looking at the ones in stock...the packages they have now no longer even say WHAT diameters the unit can be set to...so why risk spending the cash.
CHECK EBAY...the prices are better anyways.
 
Lots of modern bicycle computers have a "cadence" function that measures pedal rpm directly, with no diameter conversions necessary. They often use a magnet on the crank arm near the pedal and a sensor on the frame (the speed function uses a magnet on a spoke and a sensor on the fork). I don't know what the limit is on the measuring range for most of them; normal pedaling cadence is from 60 to 130 rpm, but it might be possible to exploit that function instead of worrying about finding one that you could calibrate for the equivalent of a tiny wheel.
 
How it works.

How it works.

Most of the units will work. The diameter of the rotor or ring gear is immaterial. I just bought a Wal-Mart Schwinn unit. It works well. Here's the math behind it:

You want to fool the unit into thinking the wheel/rotor will travel 1 km in 1 hour (it can also be done with miles, but the setting is different (see below)). 1000 meters/60 seconds = 16.667 meters or 16667mm. The devices look for a circumference in mm of 4 digits usually. 16667 won't fit. Divide by 10 and get 1666.7. Round up to 1667. Now it fits in the device entry. Your readout should show RRPM as a number divided by 10. Example: 357 RRPM will display as 35.7. You must set the device for metric (km) to use 1667.

If you are determined to use a miles setting, 5280/60=88. Convert to mm = 26822mm. Once again, divide by 10. Set the meter to miles and use a wheel diameter of 2682 mm. The result will be the same. The device will read RRPM/10.
 
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Ok, lets take this a step further........will this Ace model work with the sensor that Ernie uses (sorry, dont know the name brand) on the Dominator head? Could I simply splice into the existing mount and run the wires to the new device? Anyone tried that yet??
 
It might, but it is different mechanical logic. The sensor Ernie uses counts the metal teeth that go by and the display calculates that into RRPM. In theory, the pulse is similar, but you'd have to reverse calculate 1 revolution for each tooth on your ring gear and come up with a number that would fit in the device to decode that. I'm not sure where that would put you with regard to the bicycle device decimal limits without coming up with the equation and doing the math.

Frankly, I have had trouble getting the ring gear sensor to be reliable. The little magnet and sensor on the bicycle unit is remarkably reliable and easy to install. Why change that?

What would be cool would be to change the switches in the back of Ernie's unit to use the once-per-revolution pulse from the bicycle sensor. I like Ernie's display much better.

*JC*
 
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WOW,thanks for all the information I believe with all the help I can get one to work now.
 
Yea,

Just get one that has a "cadence" function and you're set, because it already counts 1 per 1 rev. I used the Cateye. The only hard part was splicing those microscopic wires.
 
Schwinn Rotor Tach

Schwinn Rotor Tach

FYI, as Vance would say, "to enhance the journey"
 

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Yea,

Just get one that has a "cadence" function and you're set, because it already counts 1 per 1 rev. I used the Cateye. The only hard part was splicing those microscopic wires.

Thanks - that's what I was proposing in post number 5 above, but I hadn't actually tried it. You don't have to do any math at all or enter any numbers for the cadence. My only doubt was whether it could handle, say 400 rpm (given that most bicycles will never be pedaled more than 150 rpm because humans can't make their legs go that fast), but it sounds like you've confirmed it.

The display rpm should show the number directly and correctly, with no decimal points to worry about.
 
I use the Schwinn and it works great. I extended the wire using the very thin wire found inside a standard indoor telephone line. My machine is probably 15 feet from the readout to the magnet... no problem.
 
My recommendation on the wire extension is standard single conductor shielded audio cable. This is a high-impedence pick-up and has a high loss-per-foot ratio. Simple copper wire will work, but using shielded wire, such as used for a mono microphone cable or stereo channel cable will work better. Do not use antenna wire, even though it meets the requirements of single conductor and shielded. It has built-in resistance that would contribute to signal loss.

Worst case, go to Radio Shack, buy a audio or video signal wire that has a single RCA pin connector on each end and lop off (discard via wire cutters) the connectors. It will not matter which lead on the pick-up side you use for conductor or shield, but if the wire in your device is similar, connect shield to shield and center conductor to center conductor.

*JC*
 
Yea, I used telephone wire also. I'm no electrician, but it was as close as I could find to the same gauge. And it was cheap. If I hadn't put a connector inline, it would have been really trouble free (I thought I was going to need to be able to disconnect it occasionally). As it was, the connector was finicky if the connection got disturbed. So when that happened, I just had to play with the connection a bit. I never got around to eliminating the junction before I sold the machine.
 
I think stranded wire would be a better choice than solid copper telephone wire. The telephone wire can break from vibration. Stranded wires are better at absorbing vibration. Here's a photo of Rick Martin's magnet and pickup for his bicycle speedo on his Gyrobee:
 

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I agree completely. Both standard audio and video single conductor shielded wire uses multi-strand conductors. I would also recommend the braided shield over the multi-strand non-braided shield. Some telephone wire is multi-strand, but it is still not a good choice for a high impedance application like this.

*JC*
 
Heres a pix of mine
 

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Well After the information from the forum and a phone call from Wayne I hook up a Schwinn speedometer then went flying it stayed around 34 to 35 seen it on 36 twice is this about right?
 
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