We document the effectiveness of automated (robo) calls for increasing voter participation in contrast to most published research which finds little or no effect from automated calls. We establish this finding in a large field experiment which mimics campaign behavior with a targeted, partisan get-out-the-vote campaign. Our findings show that across all treatments, automated calls led to three additional votes for every thousand subjects called during the 2014 midterm general election. Additionally, our experimental design allows for testing how the number of calls in a treatment, that is dosage, affects voter turnout. Here, results show that three extra calls increase the treatment effect to seven additional votes per thousand subjects called, but that too many additional calls decrease that effect to statistical insignificance in a six-call treatment.