So I had a commenter earlier (Hi Ben, o wizard of DIY EVs!) say that I should put a forklift motor on my go-kart. Well, Ben…it’s been done. Now this guy has a “race cart,” which is different from what I’ve got. However, he did just what you suggested – and the results are pretty crazy.
Side note: 70,000 Watts is ~94 HP. With driver, that cart probably weighs about 400 lbs. That’s roughly 4.255 lbs/hp, if you’re into power-to-weight ratios.
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.
While I didn’t get any major pictures of taking it apart, there also wasn’t much to see. The frame has been scrapped; The controller, charger, and wires are separated, and the motor has been split from the transaxle. Interestingly, the motor wasn’t directly connected to the input shaft on the transaxle. It had a planetary gearset residing between the input shaft of the transaxle and the output shaft of the motor. I’ll have to dive more into that later, but I believe it to be there as a speed reduction gear.
The controller is the part that truly interested me. Opening it up, led to this wonderful quality cell-phone picture:
So, I’ve got a Curtis 1208 – that’s GREAT, except that I can’t find hardly any information about it – Curtis’ site doesn’t even list it, so it has to be a direct OEM only part. I did eventually manage to find a manual for a 1208C, but I’m not sure how that compares to this. Either way, it looks like it’s a 12V-36V input, with a continuous rating of 55A. Peak is 75A, for 30 seconds. It has reverse, possibly even regenerative braking at 2 amps!
Can’t wait to really get to play with it!
Due to schedules, new babies, holidays, and general lack of money, nothing has happened in a while. However, I scored a MAJOR epic win at work today! The maintenance dept. had a scooter that wasn’t charging properly and was being scrapped. I stripped out all the electronics, but left the batteries behind.
Close up of the motor:
So here’s the full list of what I came away with:
- Motor Controller
- Fixed-ratio single speed transaxle
- Wiring Harness – throttle, battery meter, current limiter, battery terminals
Basically, EVERYTHING that we needed! Now, to find time to get together. I was told that it wasn’t charging the batteries – not sure if that’s the charger, or was the batteries, but I’ll be sure to find out!
Some friends of my wife and I are getting rid of an elliptical/stairmaster combo machine. My wife wants it. She says I can have her current treadmill when we pick up the elliptical! This will give us not only a bigger motor (2 HP to the current 1.25), but I’m pretty sure that it’s got a PWM controller. We’ve been having issues coming up with the $350 for parts for the controller we’ll be building, so we’ve kind of been stuck in the doldrums for a little while. I’ll take pics/vid of the disassembly and testing of components once we get time to tear into it.