# Define a custom tuning grid
myGrid <- data.frame(mtry = c(2, 3, 4, 5, 10, 20))

# Fit a model with a custom tuning grid
set.seed(42)
model <- train(
  Class ~ ., 
  data = Sonar, 
  method = "ranger",            
  tuneGrid = myGrid
)

# Plot the results
plot(model)