diff --git a/y2020/control_loops/drivetrain/BUILD b/y2020/control_loops/drivetrain/BUILD
index d03c1b9..9abb2a1 100644
--- a/y2020/control_loops/drivetrain/BUILD
+++ b/y2020/control_loops/drivetrain/BUILD
@@ -81,3 +81,20 @@
         "//frc971/control_loops/drivetrain:drivetrain_lib",
     ],
 )
+
+cc_binary(
+    name = "drivetrain_replay",
+    srcs = ["drivetrain_replay.cc"],
+    data = ["//y2020:config.json"],
+    deps = [
+        ":drivetrain_base",
+        "//aos:configuration",
+        "//aos:init",
+        "//aos/events:shm_event_loop",
+        "//aos/events:simulated_event_loop",
+        "//aos/events/logging:logger",
+        "//frc971/control_loops/drivetrain:drivetrain_lib",
+        "@com_github_gflags_gflags//:gflags",
+        "@com_github_google_glog//:glog",
+    ],
+)
diff --git a/y2020/control_loops/drivetrain/drivetrain_replay.cc b/y2020/control_loops/drivetrain/drivetrain_replay.cc
new file mode 100644
index 0000000..c7d81c2
--- /dev/null
+++ b/y2020/control_loops/drivetrain/drivetrain_replay.cc
@@ -0,0 +1,65 @@
+// This binary allows us to replay the drivetrain code over existing logfile,
+// primarily for use in testing changes to the localizer code.
+// When you run this code, it generates a new logfile with the data all
+// replayed, so that it can then be run through the plotting tool or analyzed
+// in some other way. The original drivetrain status data will be on the
+// /original/drivetrain channel.
+#include "aos/configuration.h"
+#include "aos/events/logging/logger.h"
+#include "aos/events/simulated_event_loop.h"
+#include "aos/init.h"
+#include "aos/json_to_flatbuffer.h"
+#include "aos/network/team_number.h"
+#include "frc971/control_loops/drivetrain/drivetrain.h"
+#include "gflags/gflags.h"
+#include "y2020/control_loops/drivetrain/drivetrain_base.h"
+
+DEFINE_string(logfile, "/tmp/logfile.bfbs",
+              "Name of the logfile to read from.");
+DEFINE_string(config, "y2020/config.json",
+              "Name of the config file to replay using.");
+DEFINE_string(output_file, "/tmp/replayed.bfbs",
+              "Name of the logfile to write replayed data to.");
+DEFINE_int32(team, 971, "Team number to use for logfile replay.");
+int main(int argc, char **argv) {
+  aos::InitGoogle(&argc, &argv);
+
+  aos::network::OverrideTeamNumber(FLAGS_team);
+
+  aos::InitCreate();
+
+  const aos::FlatbufferDetachedBuffer<aos::Configuration> config =
+      aos::configuration::ReadConfig(FLAGS_config);
+
+  aos::logger::LogReader reader(FLAGS_logfile, &config.message());
+  // TODO(james): Actually enforce not sending on the same buses as the logfile
+  // spews out.
+  reader.RemapLoggedChannel("/drivetrain",
+                            "frc971.control_loops.drivetrain.Status");
+  reader.RemapLoggedChannel("/drivetrain",
+                            "frc971.control_loops.drivetrain.Output");
+  reader.Register();
+
+  aos::logger::DetachedBufferWriter file_writer(FLAGS_output_file);
+  std::unique_ptr<aos::EventLoop> log_writer_event_loop =
+      reader.event_loop_factory()->MakeEventLoop("log_writer");
+  log_writer_event_loop->SkipTimingReport();
+  CHECK(nullptr == log_writer_event_loop->node());
+  aos::logger::Logger writer(&file_writer, log_writer_event_loop.get());
+
+  std::unique_ptr<aos::EventLoop> drivetrain_event_loop =
+      reader.event_loop_factory()->MakeEventLoop("drivetrain");
+  drivetrain_event_loop->SkipTimingReport();
+
+  frc971::control_loops::drivetrain::DeadReckonEkf localizer(
+      drivetrain_event_loop.get(),
+      y2020::control_loops::drivetrain::GetDrivetrainConfig());
+  frc971::control_loops::drivetrain::DrivetrainLoop drivetrain(
+      y2020::control_loops::drivetrain::GetDrivetrainConfig(),
+      drivetrain_event_loop.get(), &localizer);
+
+  reader.event_loop_factory()->Run();
+
+  aos::Cleanup();
+  return 0;
+}