Motivating a Six Sigma Team can prove to be a challenging task. When they are faced with something that seems as insurmountable as some process improvements do, it's no wonder that they can get discouraged and defeated because they cannot arrive at a solution immediately. By taking the time to work with them and make them realize that they have what it takes to complete the project, you can help keep them motivated so that they will finish the project in a good amount of time without wasting resources.
As far as professional tools go, there are many things that you can do to keep your Six Sigma Team motivated. You can definitely enlist the help of professional motivational speakers from time to time and invite the team to a private seminar where they can listen to the inspirational words of someone from outside the company. Often, hearing 'hey you can do this' from an unbiased or unrelated source is going to be much more motivational than hearing it over and over again from someone that is directly involved with the process. You can also create training sessions and skills enhancement seminars that will help to boost the confidence and self-esteem within the team both on an individual basis and as a group.
Make sure that everyone has their own specific role and title in a Six Sigma Process. This assumption of responsibility will give them more reason to be motivated because they feel like they are an important contributor to the team. You should also set goals that are achievable so that they don't get discouraged and defeated by having unrealistic goals. One very unique thing that you can do is to give each team member varying challenges that will force them to use their skills and creativity, allowing them to stay awake on the job rather than getting bored with what they're doing.
Group dynamics are critical to the success of Six Sigma Projects. As the manager in charge of the team, it is your job to allow the team to be democratic in their decisions and give everyone an even more role so that the group can operate as a whole and not as individuals. Let the team brainstorm together, and promote a positive atmosphere where people are not going to be knocked down for their creative ideas by other team members. This way, you can foster team success, which will continuously serve to motivate the team and everything that they do.