Couch Cart



Last year, Cody Rice, a guy who lived in Joshua House, pushed for us to build a "couch cart." He wanted to take one of our couches (J-House has too many), screw some wheels to the bottom, and tie it to a car to pull around. Unfortunately, he graduated before we were able to build such a couch cart. The idea was also too dangerous to reasonably achieve: We had no plan for stopping.

Since then, the idea of building a couch cart has been floating around, usually as a joke. On Christmas, Nathan received some gift card money, and decided to use it to build an electric couch cart for J-House.

First, a bit of background on Joshua House, since it helps explain why we would ever waste our money and time on motorizing a couch. J-House is a place where 14 Christian guys live. We pay rent to the church Campus House, which owns the property, and we serve the church by being a place where believers and non-believers alike can experience Christian fellowship. We refer to ourselves as the "front porch of Campus House." Part of what it means to live in Christian fellowship is having fun together, and that is why we built the couch cart. It is an investment in the future of the house, mainly as a means of community building.

After Christmas, Nathan began to research which parts would be needed to build a working cart. He asked a couple friends - mostly Justin DeRosa and Ethan Cox - for advice on the design and parts. Justin suggested chain drive with an electric motor, which is what we went with. Nathan ordered most of the parts so that they would arrive on campus a week before classes started.

During the research process, we discovered an interesting condition in Indiana state law. If your vehicle:

• Weighs less than 100lbs
• Has no more than 3 wheels
• Has a top speed of less than 20mph
• Has handlebars
• Has a place to stand while riding

It is an "electric foot scooter" and is street legal. Unfortunately, our couch cart weighs over 100lbs and has 4 wheels, but we could make the argument for the other bullet points.

The J-House Couch Cart itself is a go-kart with a couch on top. We ordered an off-the-shelf go-kart axle kit, a 1000 watt motor, wheels, and a 20Ah battery.

Once enough parts got in, Nate and Nathan drove to Menard's and bought a garden cart for the base, hence "couch cart" - not "couch kart". They brought it back and immediately began drilling holes and mounting the axle.

We had the motor, motor controller, axle, and wheels connected by Sunday, January 17th, two days before classes started. We were able to take the cart for a test drive, albeit with no couch. We sat on the battery, held the motor controller in our hands, and squeezed two people on the cart. One person would be in the back, close enough to the motor controller to control speed, and the other would sit in the front, leaning forward to steer the cart. It worked but was difficult to steer.

After a bit more testing, the motor controller burnt out. An order for a new one was placed on January 20th.

On advice from Justin, we installed a 2x4 across the handlebars for more leverage when steering. It worked great and we could comfortably steer the cart.

Meanwhile, Justin and Nathan built a box to mount the battery under the couch. The same week, they installed a 2x4 along the base of the cart to drop the couch into. We needed to find a way to store the cart inside, so we used this beam to drop the couch on and lift it off of the cart so that the entire vehicle could be moved through our back door.

We added a tea tin to mount the controls in, which was made of slightly flexible metal. After wiring the controls up, we tested it. It shorted against the tin and fried the motor controller. Another replacement was bought on January 26th and arrived on the 28th.

At this point, the cart was ready to go. It worked perfectly, with the couch on and everything. Some great videos were taken on January 28th.

On the next attempt to drive the couch cart, the motor controller burnt out for the second time. We had two of the same motor controller, so we thought we could just desolder and replace the burnt-out relay with a working one. After procrastinating on this for a bit, it seemed wise to upgrade the motor controller, since it was the weakest link. The alternative was to buy a smaller gear for the motor and reduce the required torque. On February 11th, we ordered our fourth motor controller, and we splurged to get one that was rated for 60A with a 100A peak current instead of 40A and a 60A peak current. It arrived on the 13th and was installed the same day. The cart seemed to work great.

Ethan and Nathan drove it around campus for 20 minutes or so, looping around the engineering fountain. On the way back, someone asked to take a video of them. This video ended up on Barstool Purdue. Less than 30 seconds after the video was recorded, the couch stopped moving. They were wondering what happened when Nathan asked, "What's that smell?" We burnt out the motor.

The problem was easy to diagnose: the newest motor controller's potentiometer was wired differently, and we didn't bother to fix it. If the dial was turned to max, the cart would not move, and if it was set to zero, it would travel max speed. This meant that if you attempted to drive just faster than the cart's top speed, the cart would activate its motor braking, redirecting the full power of the cart back into the motor. With this flaw, it was just a matter of time for the motor to burn out.

We bought a replacement motor on the 13th - the same kind, in addition to a smaller gear to increase our torque. The motor was in by February 17th, and the gear arrived on March 5, since we had initially ordered an incorrect size. We fixed the wiring and installed the motor a few days after it arrived, and were driving the cart successfully, keeping trips short until the gear arrived. It was also snowy in February, so we did not have any great opportunities to drive the couch around anyway.

At this point, we had a number of rides under our belt, but since J-House has 14 people - many unfamiliar with the operation of the cart, we chose to write up a rules document. This happened on Feb 28th. The one-page document includes details such as how to drive the cart (forwards, reverse, brake), battery life, rules like "don't stall" and "two-person max," details on how to store the cart, and how to recover from common failures.

The handling of the cart is mediocre at best. It makes wide turns, and can handle a 90-degree turn on the sidewalk, but is unable to make any significantly tighter turns. There is no differential or power steering, and the cart is rear-wheel drive. That said, when there is only one person on the cart, handling feels fine.

After installing the new gear, we were comfortable going for long drives. A couple of days after the gear was installed, Stephen and Nathan went for a drive around campus to stress test the cart and battery. After 50 minutes, including driving off-road and up and down hills north of campus, the cart stopped working - we had burnt out the motor again. We got Nick to pick us up and bring the cart home. This was the drive that the Exponent tweeted at us for. The ride was a good thing: it meant that we had more battery life than we could ever need. Measuring the battery voltage afterward revealed that it had only used around 50% of its charge.

A used motor was ordered from Amazon on the 8th - it was cheaper than a new one - and we installed it when it arrived on the 10th.

A few days later, Nathan dropped Ethan off at his class, and on the way back was stopped by a biker with a camera. The biker said he was from the Exponent, and he asked for Nathan's email and photo. The photo ended up in the article Police pull over "couch cart".

Another time, Nate was driving the J-House Couch Cart, he was stopped by Channel 18 news. They also asked for an interview. The Exponent interview was scheduled for March 22nd, and the Channel 18 interview was scheduled for the 27th. The Channel 18 interview eventually got rescheduled to March 31st, then pushed back again to April 1st, when it aired.

On March 21st, Joseph and Nathan were going to take the cart out for a ride to get dinner, and when they were carrying the cart outside, the wheels fell off. It seems that the slotted nuts that held the wheels to the axle were knocked off by vibrations the previous day. We were supposed to insert a wire to prevent them from falling off, but we never even bothered inserting a paperclip.

Since the interview with the Exponent was the next day, we hacked together a temporary solution: zip ties and paperclips. It worked fine. New nuts were purchased, which we will Locktite on. There was no good way to determine the nut size, so we asked a seller on Amazon, who responded within a day. Unfortunately, they did not specify the gauge, which we were able to measure after initially purchasing the incorrect size.

3/22/21 Homemade couch-car zooms around campus:

https://www.purdueexponent.org/campus/video_64f768bc-8b4c-11eb-86f8-5bc02725a9f7.html

‌The Exponent interview could have gone better. The interview was a short video, filmed on a phone with only minor edits. A semi-truck drove by during the interview, making some footage unusable. We were hoping for a wider range of questions and more opportunities to brag about the cart, but we did get out a video of us talking about our electric couch cart.

Police pull over 'couch-cart'

https://www.purdueexponent.org/campus/article_7b464ee2-8cd9-11eb-8b59-1ba93596db80.html

On March 24th, we lent the cart out to some friends to film a video. They were out for nearly two hours, and on the way back, they got pulled over by the police. That got uploaded to Barstool, and the Exponent published an article. They were driving in traffic on a somewhat busy road. The police expressed appreciation for the vehicle but asked that we keep it to sidewalks. With this feedback, we immediately updated our rules document to specify that the cart should not be driven on public roads.

The same day, Nathan visited PHYS B20. This is the room of the Society of Physics Students, a club on campus with their own electric couch. He met Braden and Emily, members of the club. Their couch cart uses the exact same motor we do (48V, 1000W), but they have two and use tank drive. They claimed a top speed of nearly 30mph, whereas we cap out closer to 12mph (or 15 with the faster gear ratio). They were in the process of replacing the motor controllers, which meant that their cart was not operational. Unfortunately, it is hard to have official club meetings under COVID policies - they need to be scheduled two weeks in advance and members must register to attend - so there is no timeline as to when the cart will be restored to an operational state.