Ground Speed Indication Options ?

I'd try an older corn planter monitor with a radar gun that is properly calibrated. There is a couple ways it could monitor speed. You could use an actual radar gun or they make some that look like a hockey puck. This way as traction went away it wood show your true speed. I have never tryed this but thought about it.

Bicycle wheel and electronic bicycle computer. It has the ability to be calibrated to substantial precision, and includes time, distance, average and max speed.

Use a 20" front wheel with knobby tire, mount a bicycle front fork on a swingarm to contact the ground just in front of your drive wheels.

Mount the bicycle speedometer per instructions, but use TEN wheel magnets instead of one... this will give TEN pulses each wheel rotation, so 10 times the signal clarity. When you pull at 4.05mph, it will read 40.5.

MANY bicycle computers have a secondary input feature for second magnet sensor that measures cadence (crank speed)... and some record it as well. I don't believe any 'log' the cadence, but one can compare cadence input to ground speed to measure SLIP.

These bicycle computers are inexpensive... $25 bucks... runs on a coin battery, and lasts well over a year.

Wanted to see what speed I was actually cutting hay at with the 190 and discbine just took a garmin with me. Are you looking for something for you on your tractor or for something to monitor others at a pull? 

Why not use a cell phone app?  Some of them are supposed to be accurat

GPS really has no accuracy at this level- you're talking a distance of 300 feet at walking speed.

Because of Selective Availablility, a guy with a GPS in his car, or his phone, or his tractor can be SITTING STILL and get a 7mph indication sideways. This occurs ON PURPOSE, at RANDOM, so that 'bad guys' can't use it against 'good guys'.

Best thing to use for a ground speed indicator, is a sensor that reads ground speed.

When you use the bicycle tire as I noted above, you'll have accurate indications of a hundredth of a mph, because you're triggering it at 10x resolution. The tire will NOT slip, and you can very precisely calibrate it using a tape measure. I highly doubt you'll find a better solution, and you certainly will not find it at a lower cost or easier build.

I use two older micro trak systems on my tractors for field work, they use magnets on the front wheel to determine ground speed, but they now have a GPS option.  I know if your front wheel comes off the ground it wouldn't tell you your speed, but when I pull it is usually in the last 10-20 feet where speed doesn't make much of a difference.

timmypuller wrote: actually a gps works just like the bicycle equipment. the more input it gets the more accurate it is... .... the marine speedometer is the way to go for just pulling. it will defininatly be the lightest and easiest to install and you will look a lot cooler without that extra wheel hanging under your tractor.

Tim... I cannot, for the life of me understand how anyone could ever make that claim.

A field monitor, using a local DGPS beacon will do a much better job than standard GPS, or a cellphone, but very few GPS receivers have a DGPS receiver, and where they do, there's rarely a DGPS transponder anywhere nearby to relay GPS timing data correction.

(A DGPS transmitter listens to satellite timecoding from a FIXED location, and then calculates the amount of 'skew' in the timing signals {mostly generated either by atmospheric conditions or selective availability}, and then transmits the CORRECTION FACTOR for each timing signal for any dGPS-equipped systems within radio earshot (a mile or so).

My cellphone, my Garmin, my TomTom, and my Faria Chesapeake SS will all indicate different speeds, varying from 2mph to 12mph, while TIED TO THE DOCK. To get an accurate indication on my boats, I use a doppler radar, and drive towards a bouy... and it's really, really obvious when the GPS signals have been skewed by 'selective availability'... not only does my speed indication go berzerk, my course indicated on the GPS plotter goes way out-of-the-channel, and my elevation indication changes. Now, I'll admit that the river does flow downhill, but from a macro perspective, it's typically pretty close to flat. I'll gain a few feet from one end of a 26-mile pool in the river, I WON"T gain 35 feet going from the gas dock to the transient overnight slip.

A 20" bicycle wheel, triggered 10 times per revolution, will turn 62.8" in one revolution, so it's trigger distance is 6.28"... or
100*12/6.28 = 191 points of measurement over that 100' pull. The bicycle computer's chronograph measures in sub-hundreths of a second, so if the pull runs 3mph, that's 4.4ft/sec, you're seeing 52.8 inches per second, and seeing over 8 pulses in one second, the end result is a speed calculation integration error easily two orders-of-magnitude more accurate than a GPS indication, especially at walking speed in course-over-ground.

Edited by DaveKamp - 13 Aug 2015 at 11:27pm

I don't know about all those numbers but I do know what works. We've been running GPS for 3 years now and never once has it said I've been moving when I'm not. Also we've never been disqualified for speed since using gps. As far as how it works on a boat I wouldn't know but I've been on boats on the water and have never seen one sit completely still so it may be reading the movement from the waves or current. A gps will not distinguish whether movement is forward ,backwards or sideways it just knows it's moving. I also use a gps in the semi I drive and never had one say I'm moving when I'm not,maybe I have a better product. As far as cell phone apps there are some that are fairly accurate but most of the free ones are not that great. My final word on this is a gps such as a marine speedometer or a calcu acre works great and I still look cooler than some one with a bicycle wheel on their tractor running down the track. If you saw my orange junk running down the track you would have to say he needs all the cool he can get.

don't come to this often but am I to believe you can't go fast in a pull  or you'll lose ?
I thought the idea was to pull a big honking weight down the track, the furthest on wins ??
Jay

timmypuller wrote: A gps will not distinguish whether movement is forward ,backwards or sideways it just knows it's moving.

The GPS knows that your moving, because it knows your position and vector, the latter being direction.

The GPS system works on a network of satellites that have stratum-2 precision clocks that are synchronized to an atomic clock on earth.

Each satellite broadcasts this time at a fixed radio frequency, and the time clock is phase-locked-loop synchronized to the frequency that the transmitter operates on. This means, the GPS bird is little more than a clock in orbit, with a radio beacon that transmit's the bird's ID and a time code.

It 'knows' it's orbit path based on ground transmitters placed at regular intervals, and as it passes, it 'hear's the ground transmitter, and determines the frequency shift that occurs by Doppler Effect. It maintains it's orbit, and transmits frequency.


Terrestrial receivers hear the GPS signal, read the time, bird's ID, and then calculate doppler shift. It does this to several other birds, and from that, the receiver can determine it's own position in 3 dimensions.

Change in position equates to movement in a vector, and the time in which that change occurs, equates to velocity. That means, going straight up, is moving just like going north, south, east, or west.

The GPS's position determination circle in 'standard' (non Mil-precision), is about 300 feet. That means, when you get a 'fix', you will most likely be within a 100 foot SPHERE of the identified position. Anywhere in that sphere (including below ground, or on an overpass, when you're really on the service road), is considered accurate.

Mil-spec puts you within 15 feet or so- close enough to get a missle in a large doorway or window, or fly an aircraft under a high-tension wire.

Selective Availability, is when the Department of Defense decides to alter the time code signal to cause the GPS to be less accurate 'for defense purposes'... i.e. some adversary decides to use an off-the-shelf GPS to remotely guide a home-made road-vehicle with an IED, or some other antic.

Getting good data isn't about how you 'look' doing it, it's how the performance numbers look after you've completed the pull.

Set your GPS unit to walking to bike for the lower speeds. Both my Garmins have it.

Now I did talk to a guy that had a radar set up on his tractor. said 800.00 to put it on, but since he had 25K in the engine, whats another 800.00

Tim ...........  I sent you a PM.... 

When running a speedometer we find its very hard to get exactly on the speed you want. I run 8 &10 mph classes.10 mph in the 8500 and 10500 open is simple to hit and hold with my 21 in 6th. Not so hard to do in 8 mph 7500 in 6th. Have enough tire slippage to keep from setting off alarm. Very hard to do 8 mph in 8500 in 6th usually drop to 5th need to put a 5 and a half in for 8 mph 8500 and 10500 . What I usually do is get it as close as I can and crank it open when I feel the weight hit.