Biologists are beginning to combine biomimetic and robotic methods to generate and test biological hypotheses about animal function and evolution. Notable progress has been made studying aquatic vertebrate systems and their locomotor mechanisms, with self-propelled physical models improving our ability to simulate complex behavioural and mechanical systems. As biomimetic robots gain popularity as model simulations, it is essential to characterize explicitly the investigator's scientific intent and method of evaluating the robot in regards to testing hypotheses. Intent and evaluation can be characterized using Webb's seven-dimensional hyperspace for biorobotic model simulations. After reviewing this hyperspace approach, it is used to discuss three different kinds of biomimetic, swimming robots that differ in their accuracy, concreteness, and specificity with regard to their biological targets. Although each robotic system occupies a different position in Webb's hyperspace, because of the investigators' choice of biological target and method of evaluation, explicit justification of the robot's position makes it clear that no single position is better than another. Thus, biomimetic robotics is a flexible modelling methodology, addressing different kinds of biological questions and, in addition, providing engineers with plausible biological mechanisms and a library of implemented biorobotic designs.