The Tractor Cart:
I initially plannned on building a vehicle which would carry two people on a front-mounted bench seat, and contain a truck bed. For the truck bed, I found that Rubbermaid makes a tractor cart that fit my needs well, and was made of light-but strong-plastic which would not rot or need maintenance (I could pick the whole 8 cu. ft. cart up with one hand). I purchased one for $148.25 from US Plastic Corp (www.usplastic.com) on Oct 25, 2002. I later decided it would be simpler to just tow the trailer behind a converted riding lawnmower. Here it is hooked up to the Toro I bought from a local lawnmower repair shop for $250 without a motor.
The Sample Load:
I wanted to test the Toro under load conditions, so I put a birdbath with a solid concrete pedestal in the cart to tow around. Though I didn’t weigh it, I would guess both pieces weighed about 100 lb or 45 kg.
The Emblem:
I wanted to have an emblem on the riding mower which showed that it was now electric powered. This is what I came up with. The ‘solar’ part was part of a longer-term plan to use solar panels to recharge the batteries. Around this time I considered naming it ‘El Toro’-short for ELectric TORO. The emblem was printed on photo paper with an inkjet printer, then attached with clear contact paper. The basic emblem was taken from the toro web site, then modified in Adobe Photodeluxe Bus. Ed. 1.1.
The Battery Pack
The batteries used were Everstart 115 amp-hour 12 volt deep-cycle marine batteries. Each cost about $65 at a local Wal Mart. The battery box was an aluminum electrical enclosure back with hard foam filling from an old ice chest lid. They were connected in series for 24 volts.
The Lights
I had to rewire the electrical system, and it worked well. I also had to rewire the two headlights from 12 volt parallel to 24 volt serial (See the black electrical tape?) They worked great and were responsible for the tractor’s later nickname ‘The $800 flashlight’. (Of course, if one bulb burns out they BOTH stop working!)
The Solenoid/Contactor
I needed a way to use the original ignition switch as an on/off switch to start the motor. I chose to use a starter solenoid since they are relatively cheap and effective for using a low current to control a high current electromechanically. Here you see the 24v solenoid purchased from EV Parts (www.evparts.com) for $18.45. It worked well, and never seemed to get hot.
The Hydrostatic Transaxle:
The Hydrogear hydrostatic transaxle was the selling point for me purchasing this riding mower. Much of my original research focused on ‘Robot Wars’ type electric vehicles to get ideas I might be able to use. I came across the ‘Run Amok’ robot (www.open.org/~joerger/detail.html) built on a riding mower chassis. The designer mentioned a hydrostatic transaxle would have been better than the one he found, so I set out to study them. I was impressed with their ability to infinitely control speed. This gave me a way to control tractor speed and direction without an expensive electronic speed control, reversing contactors, or an inefficient resistance speed control. The small pedal on the right in the photo controls this.
The Motor:
The 24 volt Magmotor (www.magmotor.com/C40.htm) I purchased for $300 at robotbooks.com (www.robotbooks.com/robot-motors.htm) had a 1/2 ” tachometer shaft on one end and a 5/8" driving shaft on the other end. On the 1/2" shaft, I mounted the original transaxle cooling fan. On the 5/8" shaft, I mounted a coupler to the transaxle. The transaxle shaft was a metric size slightly smaller than 5/8". I filled the gap with a few layers of aluminum can wrapped around the shaft. It worked well. The motor was a servomotor rated at 1 HP continuous and 3.8 HP peak. I believed this to be adequate to do the job. (The original gas engine was 16 HP)
The Test:
I took the mower around the block a few times witthout the tractor cart attached and it worked fine. To see if it would hold up under load, I tested the mower by pulling the cart with the load specified above. It successfully pulled the load about 1/2 mile before burning the armature wires. I could have replaced the armature for $200, but it would have burned out again unless I determined what went wrong. (Maybe the motor was just too small for the load). I decided to put the project on hold, then later abandoned it altogether. While it was running, it worked well--and it was fun to build. Although I had installed a 300 amp fuse, it was really intended to protect against short circuits, not motor overloading. The fuse never blew.
END
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