C124 Speedometer Accuracy

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LeThala
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C124 Speedometer Accuracy

The police set up a radar sign near my house so I took advantage of the opportunity to compare the speedometer on my C124s with my measured radar speed. The road has a 30mph speed limit and goes past the police station so I didn't want go too fast but I was able to drive by the sign at 30, 35, 40 and 45 mph. My speedometer seemed to consistently read 2 mph over the the radar reading. I then drove my car past the radar at 30mph for a comparison and both my car speedometer and the radar sign read 30mph.

I consider 2mph to be very close so I am quite pleased with the accuracy of the speedometer. My XM-3000 speedometer was so far off that it was completely useless for indicating speed. If a speedometer isn't exactly dead on accurate. I'd rather it read slightly over than slightly under so I'm never exceeding the speed limit by mistake.

John D.

Spaceangel
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Re: C124 Speedometer Accuracy

I just have to agree with you on XM-3000. I hooked up an extra DC-DC converter and plug in my Magellan and use it as a speedometer. A tad bit small to really see it but I matched it against very inaccurate XM-3000 and keep an eye on it that way. Magellan is so accurate with police radar signs in our area. So is our Chevrolet Trailblazer speedometer. BTW what is your range?

KB1UKU

LeThala
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Re: C124 Speedometer Accuracy

I haven't gone more than 12 miles yet on my C124 so I have no first hand experience regarding range. I used to get 20 on my xm-3000. This one should go twice that. At some point I'll push it to the limit to find out exactly where that is and I'll post it here.

John D.

JLGRAU
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Re: C124 Speedometer Accuracy

usually, the police will only issue a warning if you are cruising less than 5 mph over the limit. 5 mpg or more and a ticket is possible. but a bigger issue is the accuracy of your odometer if you want to know range.
measure and area of say 1 mile on your car odometer, then go over it in the 124.

LeThala
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Re: C124 Speedometer Accuracy

I didn't think of checking the odometer. I'll put that on my list of things to measure. I've been using the trip meter to measure how far I go between charges.

John D.

JLGRAU
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Re: C124 Speedometer Accuracy

I don't know anything about that particular speedometer. the one I use on my ebike has to be programmed as per tire size; otherwise, you will get inaccuracies.

MikeB
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Re: C124 Speedometer Accuracy

My Honda SilverWing's speedometer is almost exactly 10% fast, which appears to be very common for motorcycles. I've now had 3 dashboards on my C130, and each has had a different level of inaccuracy. I know my current one is reading fast, probably in the 10% range, but would have to do another test with the GPS to be sure.

Terry (one of the Current guys) created a nice setup for calibrating them in the shop, and his goal is to keep them pretty close to accurate in the 30-40mph range, but they'll end up diverging if you're going much faster or slower than that. Part of the problem is a pretty big variation in the error level as the part comes from the factory, and there's a limit to what Terry can re-adjust.

Oh, and the police radar signs are usually good, but sometimes very badly off. The best way to test a speedo is with an onboard GPS, preferably one that's mounted to the bike securely.

My electric vehicle: CuMoCo C130 scooter.

LeThala
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Re: C124 Speedometer Accuracy

Terry seems to have done a very good job of getting my setting close. I can see how being dependent on wheel diameter makes getting the speedometer on a light vehicle like a motorcycle dead accurate is almost impossible since the wheel diameter changes depending both on tire pressure and rider weight. Someday someone will make a speedo that works like an optical mouse with a camera pointing at the road and the problem will go away.

John D.

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Re: C124 Speedometer Accuracy

In the inagural commute on my C124, I noticed a distinct high anomaly in the odometry from home to work on yesterday. The reading was 6.4 miles, the known distance is 5.5 miles. So today I checked the speedometer on the way to work using a GPS. The speed indication is spot-on, although a bit of excessive damping leads to reading lag - even when accelerating and decelerating gradually.

The odometer reading, as suspected, is a fairly whopping 17% high.

This is not suprising. The usual "Chinese-scooter speed error" can be removed by adjusting the indicator needle spring. But getting the odometer to read correctly will require a change of drive gears - either at the wheel-hub or internally. In the days of mechanical speedos in cars, different size drive pinions at the transmission-end of speedo cable were availabe to calibrate speedo/odo for different tire sizes. The simplest fix would be a wheel mounted magnet-and-hall-sensor type instrument like bicyclists use, which are easily calibrated by the user. An added advantage is a bit less rolling resistance too. but these have a digital readout, which I don't particularly like in a speedometer.

jdh2550_1
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Re: C124 Speedometer Accuracy

Sorry about the odo inaccuracy. The new LCD gauge will have access to speed and distance information as calculated by the BCU. These are calculated from the hall sensor signals that also go to the controller (essentially the same as the wheel mounted magnet speedo you refer to).

John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employer
Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.

PJD
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Re: C124 Speedometer Accuracy

Yes - that is even more elegant. I hadn't occured to me that the transmissisonless motor itself provides the wheel speed indication. Someday it can be incorporated into the main instrument directly.

But, one would think that the existing Chinese supplier could be cajoled to do it right.

Johnny J
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Re: C124 Speedometer Accuracy

PJD, could you please give me a brief explaination how to adjust the indicator needle spring?

Best regards

Johnny

PJD
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Re: C124 Speedometer Accuracy

I was talking about mechanical speedometers generically.

In a mechanical speedometer, the cable spins a aluminum cup nested inside of which is a bar magnet (or vice-versa - the cable spins the magnet) Magnetic flux-induced eddy currents in the cup produce a tractive force between the cup and the magnet linearly proportional to the speed of the cup's (or magnet's) rotation. (You may have seen a similar mechanism used as a damper for old-style laboratory balance scales). The magnet is attached to the speedometer needle, which also has a watch spring (for younger people - that's a spiral-type torsion spring). The spring-constant of this spring, and it attachment point determines the calibration - the "gain" (mph or kph per cable rpm) and the zero-set point, respectively. So bending the spring or it's attachment point changes the calibration.

It is obviously a delicate operation and if you have no experience at it, you will probably damage the speedometer. But, I once net a guy who would earn a living repairing and calibrating speedometers - auto mechanics from all over the US mid-Atlantic would send him speedometers for repair and calibration - he was the only one, in the Washington DC area at least, who did it.

Johnny J
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Re: C124 Speedometer Accuracy

OK, thanks, I have a couple of extra ones for the XM-3500, will do some trials. (Sorry about the off-topic-brand). :-)

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