Arduino/Teensy distance and speed measurement. - Page 1
Forum section: electronics / projects

author: Kevman
author_rank: Regular Contributor
timestamp: May 26, 2015, 04:18:08 pm
content: So my local tractor pulling club uses one of those cheapo handheld surveyors' wheels for measuring the distance the sled has traveled. The competitions are all about distance, so this is vital to get right.The surveyors' wheels have issues- the cases keep coming apart and they develop repeatability issues quite frequently. They also do not do speed at all, requiring them to screw with car GPS things when they need that. They're also junk, working by using brass brushes against a PCB, which I suspect is causing the repeatability issues.'Professional' tractor pulling measuring systems cost like $2800. I think I can do better, even making it wireless, so it transmit distances back to the announcers' booth. Right now the sled operator tells the booth the distance by using a walkie-talkie.I'm looking at using this rotary encoder with the original 13" measurement wheel:https://www.sparkfun.com/products/10932I'd rather not use a cheap Chinese thing, but Rotary Encoders seem to be tough to find. Jameco doesn't seem to stock any and Digikey seems to only sell ones that look like pots or are like $500. Does anyone know of any other candidates?I also need some sort of display for the Arduino that is easily readable in bright sun. The original uses a transflexive LCD like a wristwatch, so I'm thinking about getting one of those Nokia LCD displays. I'd like something a little larger, though.Does anyone know if those OLED displays are readable in sunlight?

author: dom0
author_rank: Super Contributor
timestamp: May 26, 2015, 06:34:30 pm
content: Someone holding up a piece of cardboard and using a laser rangefinder isn't an option?

author: retrolefty
author_rank: Super Contributor
timestamp: May 26, 2015, 07:06:58 pm
content: QuoteYou should need look for either optical or magnetic quadrature encoders with a step count per revolution that gets you the resolution accuracy you require. They are rather pricey new but have seen real bargains on E-bay and surplus dealers. I bought 3 magnetic ones for $5 each on sale at one of those 'surplusy' dealers and when sold out never offered again.

author: dom0
author_rank: Super Contributor
timestamp: May 26, 2015, 07:08:44 pm
content: If you really want that wheel-thingy I'd just use a stepper motor as the encoder. Gives you 1.8° angular resolution. Easily sourced and essentially costs nothing.

author: zapta
author_rank: Super Contributor
timestamp: May 26, 2015, 08:02:33 pm
content: Isn't it easier to fix that tractor once so you don't need to pull it?Also, what's wrong with the tractor's odometer?I must be missing something.

author: dom0
author_rank: Super Contributor
timestamp: May 26, 2015, 08:23:00 pm
content: The odometers I know have kilometer resolution.

author: Kevman
author_rank: Regular Contributor
timestamp: May 27, 2015, 12:06:15 am
content: Quote from: dom0 on May 26, 2015, 06:34:30 pmSome clubs do that but it has issues, especially over the range of the track and if you zig zag down the track it doesn't count that distance (happens more than you might think). Also they get expensive. There is also ground radar, but even that has problem over uneven track surfaces.Quote from: retrolefty on May 26, 2015, 07:06:58 pmThat's what the Sparkfun one is- optical and 200 step per rev. That nets me something like .05" precision with a 13" wheel- over an order of magnitude than what I need but oh well. Finding other options new has been tough.Quote from: zapta on May 26, 2015, 08:02:33 pmNot sure if serious...Tractor pulls are competitions where you use a tractor to pull a sled and the winner is the person who pulls it the farthest. The sled gets harder to pull as you go.Very few tractors have odometers (they use hourmeters instead), but if you used one the winner would be who sat there and spun their tires the most.Quote from: dom0 on May 26, 2015, 07:08:44 pmI suspect that would swing from almost no detectable output at low speed to maybe enough to damage your digital pin on your micro at high speed... So it would require a buffer and also probably some biasing...

author: dom0
author_rank: Super Contributor
timestamp: May 27, 2015, 06:30:37 am
content: Quote from: Kevman on May 27, 2015, 12:06:15 amhttp://www.elektrik-trick.de/sminterf/sch_mot.png

author: Psi
author_rank: Super Contributor
timestamp: May 27, 2015, 06:44:59 am
content: You could probably repurposed some radio control gear for model aircraft. Some have a return link for GPS from the receiver.And its already wireless with plenty of range.Just need to make the frontend to take the GPS stats from the transmitter and process them into distance between points and speed vs time(In reality both are transmitters and receivers but the normal comms direction is for plane control, telemetry feed is backwards)I think the cheap open LRS clones would work. They're like $20 for tx and 20 for Rx. Its open source/firmware too

author: Fungus
author_rank: Super Contributor
timestamp: May 27, 2015, 01:31:37 pm
content: Quote from: Psi on May 27, 2015, 06:44:59 amGPS will never work for something where winners/losers could be separated by centimeters (aka. inches).