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Rudder vs Differential Thrust in Combination with THR-100X Thruster

Hello BR community,

I am developing a solar AUV/ASV, which will use its thrusters primarily for locomotion at the surface. When it dives, it is mainly for data acquisition and doesn’t need propulsion below the surface (it uses a variable ballast system). I intend to use a Blue Trail Engineering THR-100X thruster along the center axis for its primary propulsion. In addition to that, I plan to use two smaller thrusters out to the sides to generate differential thrust to turn the vehicle.

The vehicle will travel several miles offshore to 3 preprogrammed dive locations. Precision is not a priority, just general accuracy.

The vehicle is limited to 300m depth, and I intend to operate it up to that depth. A servo-based rudder won’t work because the Blue Trail Engineering servos won’t work since they aren’t rated for that pressure.

I could use two THR-100X thrusters offset to each side to power and steer the vehicle. However, it is a bit out of the current budget to purchase two.

My current plan is to use the singleTHR-100X thruster fixed on the center axis to do the majority of the forward-thrusting, and then an offset T-200 thruster on each side to generate differential thrust to give steering inputs.

I haven’t done any power budget analysis yet, and I know the T-200s are FAR less efficient than the THR-100x, but they have a great value and can easily tolerate 300m depth. I was hoping to get some feedback or alternative solutions.

The only other thing that comes to mind would be modifying a T-200 motor into a rudder system.

As a side note, the amount of thrust per watt that the THR-100X is astonishing. I’ve been designing this platform since early 2019, and when I saw the THR-100X come out, it was jaw-dropping, so hats off to Damon McMillan at Blue Trail Engineering.

Thanks for the help, guys,

Tyler Sims

Hi Tyler,

I’m glad you’ve seen my THR-100X thruster. Efficiency is all about propeller diameter and the choice of motor, and I’ve tried to optimize those factors in designing this thruster. Of course, it comes at a cost: the motor itself is expensive, and a magnetic coupling is required. The T-200 is an amazing piece of machinery and the better (and much less expensive) option for ROVs, but if you’re building a long-endurance ASV or AUV and must have efficiency, a thruster like the THR-100X is the ticket.

If you use two smaller thrusters on the side, that will defeat the purpose of having an efficient main thruster, since the two smaller thrusters will cause a ton of drag when they’re not spinning.

Our Blue Trail servos can be filled with oil, giving them a max depth rating of 600m. I don’t advertise that on our website, but if you’d like to pursue that, please send me a personal message.

And last but not least, I’m excited to hear about your boat! Please post pictures when you have them!


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Rudder would definitely be more energy efficient.

How about a rim drive bow thruster?