Limits
If we make the speed huge, r also becomes huge. A huge r makes the circle so big that any small part of that circle looks to be fairly straight. This would make aiming the particle easy - just like it was for no charge. However, we cannot physically make the speed of a particle that huge. The program takes this into account by limiting the speed to about 1/10 the speed of light ( max speed allowed is 3 x 107 m/s).