I loved the transformers in grade school. This is my design of the micro series that were similar to penny racers. They were released in the late 80's.
I've included the head as a single part for single extrusion as well as a dual part for dual extrusion as seen in the photos.
I printed everything in PLA at .15 with 50% infill. Supports were used on some parts. Using supports on the parts of the arm that slide into the body helps to make the arms stiffer when pulled out as the imperfections left from the supports create friction.
Clean up parts and press together. The model pictured is all press fit. A drop of glue where parts fit together would prevent any slippage as you change from one form to the other.
I used Fusion360 and a Flashforge Inventor with Inland PLA.