I’m alive! I’m here! Welcome back all. Not much has happened due to new jobs, home remodeling, and paying bills. The Jetta has been re-arranged in the garage, and the go-kart has been moved to a more accessible location. Hopefully from here on things will pick up – albeit slowly.
The current (heh) situation of the go-kart is this: The controller from the mobility scooter is strapped up and working. It’s 24V, 50 amp continuous, with a 30 second 75 amp peak. The motor is rated for 1.25 HP at 120VDC. Drive sprocket was 14 tooth, connected to a 60 tooth axle sprocket. This gave a drive ratio of ~4.286:1, and no usable speed (kart moved, but only if no one was sitting in it.
I’ve found a 10-tooth drive sprocket, but have to get the center bore enlarged. That’ll increase the ratio to 6:1, which will boost torque by 40%, even though it’ll reduce our top speed by 27%.
With any luck, I’ll be able to get the 10 tooth sprocket machined this weekend and maybe be able to test it out on Monday or Tuesday.
The throttle needs some sort of permanent mounting, but I haven’t figured that out yet.
So I did some of the math today. Problem with the go-kart actually going is definitely gears. We’re waaayyyyyyyyyyy too low of a ratio at the moment. Sure, more power would solve the problem easily. However, let’s look at the math:
6000 RPM electric motor
20″ diameter tires
14:60 drive ratio (~4.28)
6000 RPM input / 4.28 motor:axle ratio = 1401.869 axle RPM; let’s call it 1402. So axle (and tires) are doing 1402 RPM at max motor speed (which is where DC motors run the best/coolest/most efficiently).
20″ diameter * 3.14159 = 62.832 inch circumference of the tire.
62.832 / 12 inches per foot = 5.236 foot circumference
1402 RPM * 5.236 feet/rev = 7340.872 feet/min
See the problem yet?
60 MPH = 1 mile per minute
1 mile = 5280 feet DING-DING-DING-DING-DING! You should see the problem by now……
7340.872/5280 = 1.3903 miles/minute * 60 miles/hour = 83.419 miles/hour
We do NOT need to be tearing around at practically 85 miles an hour on a go-kart when the motor is running at its best! I’m not sure what to do about correcting this myself; perhaps others have ideas on how to just about double the drive ratio? What’s the best way to go from 4.28:1 ratio to something more like 9:1?
Got a few minutes to go play with/on the go-kart tonight. Strapped down all the loose wiring, pumped up the tires from the 2 or 3 PSI that was in them to about 20 (or so). I also reversed the motor connections, so that when “FORWARD” was pressed on the throttle assembly, it went forward (instead of backwards).
Insert key, hear the standard ‘click’ of the relays opening/closing. Sloooowly twist on the throttle…and it moved! Slow, but without any assistance from me or being pointed downhill!
I was right – at 50 amps (75 peak for I think 10 seconds), it’s little more than an oversized ‘Power Wheels’ car for adults. I don’t care. It moved.
Over the weekend, I managed to get time to put everything together for on the electric go-kart that is sitting in my garage. While it will be (and is) its own project, our plan is also to use it as a “test bed” for a medium controller, as well as our full-size one for the Jetta.
I snapped a few cell phone pics of the kart all wired up in the back:
As you can see, it is relatively temporary.