Project
owner
Victor Motti — Interaction & experience design
Grocery Trip
01
Case
file
GT
Project
alias
Alt. controller
Two-player arcade
Physical game feel
Case file GT-01
2022 — 2023
A two-player arcade game you play by pushing a real shopping cart. One player drives, the other grabs. Prototyped in 3 weeks, then selected to be shown at GDC 2023.
Discipline
Game design · Interaction · Hardware
Shown at
GDC 2023 · San Francisco
Years
2022 — 2023
Fig. 01
Playtest on the show floor — GDC 2023
S.01
03
Weeks from idea to playable
GT01-S01-WK
S.02
04
Parameters tuned for game feel
GT01-S02-PRM
S.03
200+
Players in 3 days at GDC
GT01-S03-PLY
S.04
11×
Runs by one player, in a row
GT01-S04-RUN
01
The game
Sec.01 — GT-01
A crazy grocery race.
You’re at the supermarket. The list is long, the timer is short. One of you drives the cart, the other grabs items off the shelves. Other shoppers in the way? Shove them.
Clip 01 — Driving
P1
Player 1 steers the cart through the aisles.
Clip 02 — Grabbing
P2
Player 2 snatches items off the shelves.
Clip 03 — Shoving
P2
Player 2 pushes other shoppers out of the way.
Player objective
Grab as many groceries as you can before the timer runs out.
Fig. 02 — The childhood memory behind the split
The key decision
One controller, two players.
The idea came from a childhood memory: being the kid in the cart while a parent races through the aisles. So we split one controller between two players.
Player 1
P1
The parent
Drive
Steer & boost
Navigate
Find the way, dodge obstacles
Player 2
P2
The child
Grab
Reach and snatch
Punch
Push other shoppers aside
One choice, three design consequences
C.01
Cognitive load
Each player handles two actions instead of four.
C.02
Cooperation
Players have to sync up to score.
C.03
Divided input
A strange controller becomes manageable when it’s shared.
Grocery Trip
GT-01
Alt. controller
1 cart / 2 players
Game feel
GDC 2023 — San Francisco
02
Game feel
Sec.02 — GT-01
Making a cart feel fun.
A shopping cart is annoying to push in real life. That was our raw material. The job: turn the friction of a clumsy object into the pleasure of a well-tuned one.
Phase 01
On screen
First, we tuned it on keyboards.
Arrow keys, a laptop and a free vehicle script. A few tweaks later, the cart felt workable. Not great, but playable.
“It almost felt right.”
Phase 02
On the cart
Then we plugged the controller in.
Same code, same physics. Different planet. The cart drifted past aisles, hit walls, refused to turn. Players stopped laughing and started apologizing.
“A tank on a frozen lake.”
Phase 03
The tuning
Four parameters. Dozens of playtests.
We grabbed anyone passing by and watched one thing: did they smile while playing? Too much acceleration, an F1 in sand. Too little, a tank. The right answer was always between two failures.
Tuning notebook
4 parameters
P.01 — Acceleration
Bumps into every wall
P.02 — Turning radius
Slides past every aisle
P.03 — Ground grip
Ice rink
P.04 — Braking
Stops instantly, or slides forever
Switch to compare the cart before and after tuning
Field note // Phase 03
There was no single moment when it clicked. Just a slow convergence, test after test, until the cart stopped feeling like a problem and started feeling like a ride.
Too fast — F1 in sand
Playtests →
Too slow — the tank
Sweet spot
Diagram — illustrative, not measured data
03
Hardware
Sec.03 — GT-01
Wiring the cart.
I led the wiring: steering sensors, driver controls and the input board that turns physical gestures into game inputs. I had never wired anything before. I learned on this cart.
01
Steering sensors
Read which way the handle turns to steer the cart.
02
Driver controls
The inputs that move the cart forward or backward.
Fig. 03 — Input map
4 points
NTS · Scale 1:2
GT-01 / HW
03
Grab & punch pads
Pressure pads the second player hits to grab or shove.
04
Input board
Turns every physical input into a signal Unity can read.
Fig. 04 — The cart in action
What I learned
L.01
Adding a sensor is a design decision, not just a technical part.
L.02
Cables are invisible UX too. If a wire gets in the way of a hand, the player feels it before seeing it.
L.03
Hardware iterates like software: think, test, adjust. With a soldering iron.
04
GDC 2023
Sec.04 — GT-01
Selected for GDC 2023.
We applied to exhibit at GDC 2023 in San Francisco, the largest conference for game industry professionals. We got in.
Fig. 05 — On the show floor
Fig. 06 — The build
Fig. 07 — The unfold
Fig. 08 — The assembly
Fig. 09 — The setup
Event
GDC 2023
Zone
alt.ctrl.GDC
City
San Francisco
GDC23-ALTCTRL-GT01
How we got there
We couldn’t fly a real shopping cart to San Francisco. So we rebuilt one in wood, foldable, collapsing into a flight-safe box with everything the game needs to run.
The test that mattered
We knew the game feel worked when players laughed mid-game. Mid-game laughter means the controller has disappeared, and only the game remains.
11×
One player came back 11 times in a row, chasing the leaderboard.
alt.ctrl.GDC
200+ players
3 days on the floor
11 runs in a row
Built to fly
Flight-safe cart
Next case file // EV-02