Introduction: Electric Snowcat Pico
This electric tracked vehicle will turn all your winter trails into "downhill" fun. The intention was to build an electric snow vehicle that would allow me to zoom around on the network of trails around my house without getting sneered at (walking trails) or licensed (snowmobile trails). The initial design was a board driven by tracks with a ski in the front (photo in step 2). While researching for a solution for steering I stumbled upon a video for a skizee. http://skizee.ca/. This innovative design not only solved my steering and suspension worries, but it looks like a ton of fun. The advantages of my scrapyard EV version described herein include the relative silence of the setup (less sneering on paths) and is too slow to worry about it slamming into you if you wipe out... A second motivation for this project was to learn the skills needed for an eventual micro car EV conversion (BMW Isetta?).
UPDATE: It gets pretty rough back there... I was able to take a few trips before I had a major breakdown. A connection was broken at the switch in the battery pack. I successfully soldered it back together; however I am not willing to risk further damaging my 500$ LiPo battery. I cant really add any suspension to cushion the blows, so I have elected to retire the Pico for now. I can only guess the speed at 10k/h and range at 10km (1 hour) given how long the battery lasts on my similarly powered ebike motor. I had a blast building it so there are absolutely no regrets.
Jump to the last step to see a video of the PICO in action.
Step 1: STEP 2: What You Need
- Wrench and socket sets
- Angle grinder
- Sheet metal brake
- Sheet metal snips
- Used tracked-snow blower/thrower. Sears made several models recently for which parts are still available; hitting-up some repair shops or scrapyards this spring might just land you one for free. Make sure to check the condition of the track and the cogs that drive them, they were not designed for endurance.
- Electric motor, controller and throttle. I did not have one that was sufficiently powerful lying around so I ordered one online: http://www.monsterscooterparts.com/48v-1000w-motor-controller-throttle-kit.html. When selecting your motor you must match your watts, amps and voltage to your controller and battery. In general watts=power (1000 watts ≈ 1.3 horsepower); however to attain its potential you need sufficient voltage (48v) and amps (≈20). I bought this kit so I knew it all fit together. There are tonnes of electric scooters available on craigslist: people don't maintain the batteries so they end up not holding their charge; otherwise everything works fine. They are typically lower power though (300-500 watts).
- Battery. (http://www.goldenmotor.ca/products/48V10AH-LiFePO4-Aluminum-Cased-Battery.html) I have the Lithium battery (LiFePO4) that I use in the summer on my e-bike. http://teamluguy.blogspot.ca/2011/09/nerd-cycle.html. This is the most expensive and most important investment. You can save some cash by using lead-acid batteries, however these will mean a significant increase in weight (≈33% of the energy density). This translates into a decrease in efficiency and overall thrust not to mention the design implications and longevity.
- Sheet metal (4' by 2') and tubing (8').
- Spray-paint and stickers for decoration.
Step 2: STEP 2: Salvage
You can't really plan your project till you've taken the snow blower/thrower apart to see what the possibilities are. In my case, all the unbolting did not really provide me with a decent view of the innards. Thererfore I resorted to the angle grinder to lobotomize the gearbox housing. This is a good stage to stop for a few days and weigh all your options. My initial design involved a board from an unfinished project (turf deville), however after discovering the skizee design, I quickly changed my focus.
Step 3: STEP 3: Install Motor
I initially thought that the motor would be sufficiently powerful to drive the tracks without the extra set of sprockets that were included. Although it did move forward in ideal circumstances; it was really on the limit for the my setup and totally insufficient for pushing me around in real conditions. I would have liked to just decrease the sprocket on the motor to get more torque, however it was already very small (8 teeth). So I decided to re-install the bar with a pair of sprockets which would provide about 4 times the torque (and theoretically 4 times less top speed). I was surprised by how much power it provided, and it ended up having a higher top speed because the motor is allowed to run closer to its most efficient RPM (3000). I was fortunate that sufficient space to bolt the motor directly on the body, new holes were drilled matching the bolt pattern for the motor mount.
Step 4: STEP 4: Body Building
Electronics and water do not mix particularly well; trust me. To protect your investment, you will want create a protective shell of some sort. I used some cling wrap and tape as a temporary weatherproofing for some field tests. For the final version I opted for some sheet metal enclosures. It is always a good idea to test out your design on some thin cardboard or thick paper. This will save you precious time, and it will definitively improve your final design. Don't forget that sheet metal has a thickness and will not bend perfectly square. I find that measuring and lining up with the corresponding part after each bend often resulted in significant adjustments from the initial plan.
Keep in mind that wires are going to have to penetrate your new fortifications somehow, and you will inevitably be peeling everything off for troubleshooting. Some silicone in the various holes will help ensure that no snow or water get in.
Step 5: STEP 5: T-Bar and Throttle
I could have called this vehicle "Mobile T-Bar" because it basically pushes your butt around (not particularly inspiring name though). I needed to create a system to direct the energy from the Snowcat to my body with enough distance to allow for skis and safety. The initial design was somewhat flimsy, so I added some angled cross beams. All the pieces were welded together with a 90 amp flux core welder using 0.03" wire. This was my first welding project, and it was easier than expected. The welds are fugly but holding well. The angle bar was slightly too large to fit in the throttle so I squeezed it with the vice until it fit snugly.
Step 6: STEP 6: Wiring
These things never end up working the first time. For example the connectors that came with the motor-kit did not match with my battery, and I had way more wires than I needed (brake lights, horn, etc.) A proper electronics store should be able to help you, don't forget to bring ALL your gear. It is worthwhile to wire everything on your workbench before installation to ensure that it is working. Test the drive direction! Many motors will allow you to simply reverse the wires to reverse the rotation. When installing your controller, try to consider what would happen if you have a chain break or fall off.
Electronics and freezing temperatures are not friends. In particular all current batteries perform poorly at low temperatures. Therefore i cut some sleeves of an old shirt which I slid over the battery during the use. I also wrapped any exposed wires in some hockey stick tape to help keep them from breaking. I've seen wires for Snowmobile helmet warmers snap in arctic conditions (-38ºC or -37°F).
Step 7: STEP 7: Test Run
Step 8: STEP 8: Finishing Touches
- Paint the key areas black (stripe down the center, and the sides) with spray paint. Read the instructions for your spray paint; you can often apply additional coats every 30 minutes (4 coats in my case). Many thin coats are better than few thick ones to avoid drips;
- Cover the areas that are intended as black with painters tape, take care to center and line it up perfectly. Make sure to push the tape into the crevices and rub the edges firmly with your finger;
- Paint the entire surface with the orange, I applied 4 coats;
- Carefully peel the tape right after your last coat.
Step 9: STEP 9: Leave Some Tracks
I've taken the Pico out for a few rides now and its is a blast to ride. You need to have a fairly well packed trail due to the low clearance (you can see the front plow the snow in the video below). The speed is not adrenaline inducing, but not geriatric either. I would love to take a skizee for a ride one day (http://skizee.ca/); and maybe convert that too.
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