GPS Speed Adapter for the most uncommon mods

[steveo]

that's a cool toy

but my eyes, in a marine application, gps speed isn't really an appropriate input for something like a VSS, especially in the salt or rivers in diverse conditions.

why? because of current.

think about it. gps is speed over ground, pitot tube or paddlewheel is speed over water.

example 1: you have a 5mph ocean current at your back. you're at dead idle in neutral. prop isn't moving. your 'gps vss' reads 5mph. a paddlewheel would read speed over water of ~0mph.

example 2: you are fighting a hell of a storm, head on into current, and some big rollers. you have this thing FLOORED trying to get home. you are NOT winning this battle. gps speed varies between -10mph and +2mph, despite your boat working its ass off and speed over water exceeding 30mph.

of course gps speed is the most useful metric for display speed in a boat since you equate it to travel time.

in the same token, gps speed is the shits for a rolling vehicle because it doesn't compensate for angle of hills (gps speed up a steep hill is as the crow flies, not as the car drives)

will it really matter? probably not, but on a boat i'd way rather have speed-over-water input for both datalogging and speed-related ecm parameters

[KidTurbo]

of course gps speed is the most useful metric for display speed in a boat since you equate it to travel time.

I'm all about speed...



Hauling butt, while also being about the "Greenest" thing out on the water has an added cool factor. If I could only find a totaled Tesla S for a good deal to play with, I'd step it up another notch.

Your point is a good one Steveo. In something like a larger boat where your making 10-15 knots having a true speed over water would make more sense. As far as reliability, I've also use DD tach adapter for the analog dash gauge for 4yrs now. Both units are mounted under the dash, but not sealed and exposed to moisture. Last month I tested the salt water impact by running 25 miles in heavy off shore chop. Everything in the boat had a coating of salt when I made it to the trailer.. I would defiantly seal that unit up if was in more of a "fishing boat" environment.

[EagleMark]

Just a little bit more chop in the water and you'd have had blown past 80!

It's amazing how 80 MPH on water feels like twice that on land. Nice work, not much noise either! I like it!

[brian617]

not much noise either! I like it!

What?! Sounds like an F-14 on a fly by

[dave w]

What?! Sounds like an F-14 on a fly by

Wow, you just dated yourself ... the F14's were retired form service in 2006.

dave w

[brian617]

Wow, you just dated yourself ... the F14's were retired form service in 2006.

dave w

Maverick: Tower, this is Ghost Rider requesting a flyby.
Air Boss Johnson: Negative, Ghost Rider, the pattern is full.

[KidTurbo]

What?! Sounds like an F-14 on a fly by

LOL, that's a fairly common comparison I hear... The sound comes from a mix of straight cut gears in the out-drive, twin 4" exhaust outlets, and the turbo inlet being directly under that scoop on the hatch. Since everything faces to the back, it's actually pretty quiet inside the boat.

But I got a bright idea one day to turn that scoop around. Force more cool air into the engine bay. And by the end of the weekend, it was switched back....

[Six_Shooter]

that's a cool toy

but my eyes, in a marine application, gps speed isn't really an appropriate input for something like a VSS, especially in the salt or rivers in diverse conditions.

why? because of current.

think about it. gps is speed over ground, pitot tube or paddlewheel is speed over water.

example 1: you have a 5mph ocean current at your back. you're at dead idle in neutral. prop isn't moving. your 'gps vss' reads 5mph. a paddlewheel would read speed over water of ~0mph.

example 2: you are fighting a hell of a storm, head on into current, and some big rollers. you have this thing FLOORED trying to get home. you are NOT winning this battle. gps speed varies between -10mph and +2mph, despite your boat working its ass off and speed over water exceeding 30mph.

of course gps speed is the most useful metric for display speed in a boat since you equate it to travel time.

in the same token, gps speed is the shits for a rolling vehicle because it doesn't compensate for angle of hills (gps speed up a steep hill is as the crow flies, not as the car drives)

will it really matter? probably not, but on a boat i'd way rather have speed-over-water input for both datalogging and speed-related ecm parameters

This actually gave me more reason to not like these add-on GPS units for a typical conversion.

In the Datsun S30 world people are swarming to GPS based speedos, because it's "difficult" to create a proper VSS signal, and then calibrating, oh man that takes "forever". :facepalm:

My main problem with something like this is that any GPS unit I have used, personal navigation, smart phones, a couple laptop dongles all took a considerable amount of time to find satellites, even on clear days. There were days I would drive several miles before a good enough GPS signal was found. Now these were positioning based systems, but AFAIK the speed only based systems need the same 3 satellites minimum to provide an accurate speed. Even though I may not necessarily use my speedo as intended, I do like to know just what speed I am traveling at whenever the vehicle is moving. I can see overcast and story days being an issue as well. There are also areas where there are structures, like tunnels that could cause the signals to be lost.

I have yet to have any real issue re-creating a proper VSS input for an ECM or cruise control in several swaps, mechanically. Yeah it may have taken a while to sort out the wheels and sensor location but I know it works, and it's in-expensive to assemble.

Don't get me wrong, I do like the idea of a GPS speed sender, more as a back up, or being able to provide positioning data than just speed, but I just can't justify the prices I have seen and the known GPS issues I have experienced and read about other people experiencing. It's good to hear some positive reviews of something that works, for when the need arises.

[steveo]

you know, a GPS speed with a level sensor so it could figure out the whole 'going up a hill' issue could be a bit more accurate on a road vehicle, but afaik you're talking some law breaking stuff here too

a drivetrain driven speedo is legally required in every damn place i'm aware of; and pretty sure a functional odometer is too.

also...... 'sorry officer, i didn't think i was speeding! my gps signal died when i went under that bridge, and the accelerometer must have been thrown off by those pot holes!'

yeah right

[EagleMark]

I never took into consideration the GPS Satellite connection... yeah this is a major issue?

[KidTurbo]

I never took into consideration the GPS Satellite connection... yeah this is a major issue?

Time to acquire a lock was a major concern for my VSS project. However one of the things I like about this manufacture, they seem to have some pretty smart engineers. The custom Harley crowd swears by their digital gauge clusters and speedometers. The engineers used two theories to overcome the normal acquisition delay and signal loss problems.

First, it attempts to never lose the GPS position lock. While part of the circuit sleeps when key is off, but the GPS chip is always kept active, so it has zero lag time on start up. A small red LED flashes every 30 seconds or so to show it's working.

Second, they added an accelerometer chip to the circuitry, and some pretty darn good logic to boot. If does lose the GPS signal, it switches over to the accelerometer for calculating speed data until GPS lock is recovered. Kinda like having a G-Tech unit built in.. Most modern factory automotive in-dash Nav units also employ this technique to deal with tunnels and such now. It knows you were last moving at XX mph, and if your speeding up or slowing down.

I had forgotten about it having the ignition switch connection in my post above. But also that it has cruise control capabilities built in. The manual for this thing is actually a "good read"



I mounted it under the dash where is has partial view of the sky. Next to my OBDII plug. The dash covering it is 3/4 plywood laminated with fiberglass and gelcoat. I'm amazed it works so well without a remote mounted antenna, or good line of sight.