Tarantula in Albuquerque

[SDCoston]

I had this old bike computer lying around, and it has the ability to measure speed as well as pedaling cadence. I spent some time tonight mounting the cadence sensor magnets to the back side of the inner plate of my TC2 CVT driver wheel and gluing the reed switch cadence sensor to the adjacent CVT mounting plate. I wasn't sure if the computer could handle sensing the high engine RPMs (a typical bike crankarm cadence is less than 120 RPM). So I started up my motor and the bike computer display said my cadence was 1250 - so I believe that to be my accurate idle rpms! It was dark out so I didnt get a chance to see if it continues to work at higher rpms. Tomorrow I mount the other magnet to the axle and the "wheel" sensor to the sub-frame over the axle at the magnet location - then i'll have a speedometer/tachometer.

Fun stuff.

 

[supermanotorious]

have a smart phone? there are many free apps that provide speed, distance, etc based on satellite, I use one for the kart and while snowboarding

 

[SDCoston]

Yeah, funny enough... I use a smart phone app on my bike. But i'm going to use a bike computer on my kart. The smart phone GPS can be configured to "update" the GPS signal up to 5 times a second. But in my experience, most apps can't update the current speed more than once every 2 secs or so. This is too slow for a cart... by the time the GPS says i'm going 20 mph, i'm already at 30!

Besides, the cell phone app can't tell me what tachometer reading my motor is at.

 

[SDCoston]

OK, after I got it all set up - it looks as if the bike computer tachometer doesn't work at rpms above 1600. Up there, the reading "jostles" all around between 1300 and 1600. Either the magnetic reed switch can't handle being triggered 3500 times a minute or the bike computer processor can't process feedback that fast.

I think my next step will be to construct an Arduino microprocessor-based go-kart computer which will measure the tach off of the magneto. My son also wants to be able to control some blinkers and headlights so I'll have the Arduino drive those things as well.

Our go-kart's max speed is exactly 36.8 per the bike computer ... just as calculated using the .9:1 overdrive ratio of the CVT. I'm wondering if I could get more speed with my 13 hp motor if I down-sized my axle ring. Is that advisable?

 

[r97]

It is worth a try, just keep in mind that if you gear too low you put more force on that belt, making it more likely to shred. I would try to gear for 40-45mph and see how that works. I like what you are doing with the Arduino, I was really into that stuff for a while. Unfortunately the small bits of information I learned have escaped me.

 

[SDCoston]

I've made tons of Arduino projects. Shouldn't be an issue. When i'm done, I'll publish links here.

 

[JCB003]

Thanks for the pics and write-up. You don't need a spring on the pedal?

 

[OzFab]

You don't need a spring on the pedal?

Better to have it & not need it than need it & not have it.
It's a spring, I doubt it will break the bank or effect performance in any way

 

[SDCoston]

I bought a spring. Just haven't installed it yet. I'm still not entirely convinced I like my pedals the way they are. I may build some upper rails up front and suspend pedals so they hang down and figure out linkages so they aren't in the way of the feet.

 

[OzFab]

One thing you will notice with everything I do is I tend to over analyse, over think & over engineer everything. I have to keep reminding myself to KISS (Keep It Simple Stupid): If it ain't broke, don't fix it.

At the end of the day, it's your choice but, speaking from experience, over thinking can lead to more than one type of headache

 

[SDCoston]

"If it ain't broke, don't fix it."

True enough. But this forum and group is all about not just getting a go kart thrown together but also about making something that works well. I'm just discussing issues with this particular design. Built the way the Spidercarts plans indicate, the Tarantula has issues with the linkage rods off the pedals and the tie-end rods getting in the way of the feet.

Don't get me wrong ... this kart is kick-a-- fun to ride, but why not talk about how to get rid of some of the minor annoyances.

 

[OzFab]

True, I was just thinking that suspending them would create more problems.

I assume the setup in the pics a page back is not the final setup; here's a simply thought: For the brake pedal, have the linkage come out the other side of the pedal closer to the side rail or even on top of the rail

 

[SDCoston]

Go-kart computer

I've almost finished building and installing our Go-kart's computer. Pics and a video sometime in the next few days. It will measure distance, speed, keep an odometer reading. It has a well-functioning tachometer. I've added headlights and rear LED lights with turn blinker's (at my son's request) and the computer will control the blinkers and an aftermarket horn as well. I'm still playing around with getting the speed to display right as the update cycle of the Arduino processor is faster than the revolution time for the live axle.

 

[souperman000]

wow, sounds like you put some pretty cool stuff on there. Are your lights on a charging coil or just a battery?

 

[SDCoston]

wow, sounds like you put some pretty cool stuff on there. Are your lights on a charging coil or just a battery?

I bought a small "ATV" lithium-ferrous battery - weighs nothing. Has a 9Ah capacity. I have a hobby charger I can trickle charge it about every 2 hours of headlight usage, which will be rare. Everything else pulls 10's of milliamps.

My engine - a Honda GX390 - doesn't have a coil and it is not electric start.

 

[Aladinbama]

That's a PRETTY IMPRESSIVE build SD!
I think I would add a front bumper, just in case! LOL!

 

[r97]

Sounds great, I can't wait for pictures! Is the display digital or analog?

 

[SDCoston]

computer

It has been some time since I promised to post pics about my kart's computer.

It is an Arduino clone based computer with inputs from the CVT and the axle using Hall effect sensors and magnets. This allows ability to compute and display tachometer and speed info. Also odometer and trip distance can be computed and displayed, as well as average trip speed and maximum trip speed.

I have the rear 3-cluster LED light strip attached to the computer using NPN switching transistors so the computer can blink them to signal turns.

I mounted it all onto a 1/4" plywood wedge that fits into the steering wheel and is all held in place with zip ties. The wiring is messy now, but once i have it all worked out perfectly and the Kart has been painted and reassembled I'll bundle the wires to clean things up.

I'm getting ground loop feedback interference from the switches controlling the 12V lights, horn, and LED strip, so I'm planning on using optical isolators to control the switching transistors and completely isolate the Arduino and the Hall effect sensors on a separate power circuit.

Here are some photos:
1 and 2 - the sensors on the CVT and hanging off the rear subframe over the live axle.

3 and 4 - the computer itself mounted and the messy wiring.

5 and 6 - The headlights and the rear LED strip

If anyone's interested, I can try to post the Arduino wiring schematic and loaded code later when I've got it working perfectly the way I want.

SDC

 

[SDCoston]

video of computer showing tach

I had time to take a video of the computer with the engine running and revved up a bit to show the tach working. Sorry about the poor quality - I'll see if I can figure out how to get more clarity next time.

http://m.youtube.com/watch?v=OWaj6jj2qGg