2550 and Differential Mixing

15 years 2 months ago #3868167 by DScott
2550 and Differential Mixing was created by DScott
Hi,
I'm building an RC/autonomous boat and want to attempt differential motor control instead of pivoting a trolling motor. Right now the motor movement (rudder) is controlled by a BIG servo on a single RC channel and thrust is controlled via the 2550 via an RC channel.
I want to steer by con tolling 2 motors instead of 'rudder' steering. Does anyone have any suggestions on a mixer I might use (or any suggestions) or how this might be accomplished?
Thanks

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15 years 2 months ago #3868738 by cosma
Replied by cosma on topic Re:2550 and Differential Mixing
The AX2550 supports differential mixing. All you need to do is connect one motor on each of the outputs and configure the controller to operate in mixed mode.

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15 years 2 months ago #3874201 by DScott
Replied by DScott on topic Re:2550 and Differential Mixing
Hi,
Thanks for the quick reply. I'm a little confused as to whether to use the 'A & B Speed Mixed' or the 'A Speed, B position' (from the configuration utility). Are these the same as what the manual calls 'Open Loop, Mixed Speed Control'?
Will R/C CH1 as throttle (speed) and CH2 as Rudder (position) be mixed in the controller if it is configured 'A Speed, B Position'?
Will that give me differential steering and speed?
I'm a bit inexperienced in this.
Thanks

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15 years 2 months ago #3874295 by cosma
Replied by cosma on topic Re:2550 and Differential Mixing

In this case, you will be operating each channel in Open Loop, Speed Control, Mixed.
When you move the joystick forward and back, both motors will go forward or back. If you move the joystick left or right, the speed and even direction will be different on each motor, thus allowing you to steer.

In this setup, you no longer have a rudder. Turning is done by adjusting the thrust and direction of the left and right motor.

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15 years 2 months ago #3878811 by DScott
Replied by DScott on topic Re:2550 and Differential Mixing
Thanks Cosma. I'll give it a try.

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15 years 2 months ago #3919095 by sww
Replied by sww on topic Re:2550 and Differential Mixing
I have done used the AX2550 to do exactly what your are talking about. Control an autonomous boat with differential thrust. It works fine.
I use control mode 1 = Mixed A&B, open loop.

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15 years 2 months ago #3920217 by DScott
Replied by DScott on topic Re:2550 and Differential Mixing
SWW,
The original design was to use a single trolling motor steered by a large (27ft/lb)servo with the 2550 controlling the thrust. We've decided to try the differential steering.I'm using a Futaba T9CAP controller with one joystick configured for thrust (Up/down =forward/reverse) and steering (left/right). This takes up 2 RC channels. We will be using a modified UAV autopilot to take the place of the steering and cut in manually when we wish.
I set up my 2550 in mixed A&B, open loop. 2550 CH1 Motor out goes to trolling motor 1 and CH2 goes to trolling motor 2. 2550 DB15 CH1 goes to RC throttle channel and DB15 CH2 goes to rudder.
When I throttle up the props spin in opposite directions (wiring OK).If I set the throttle at a left or right deflection stops the correct prop while the other goes keeps turning. Trying to make sense of the counter rotating props??? And is this operation correct. Any input would be appreciated.

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15 years 2 months ago #3922143 by cosma
Replied by cosma on topic Re:2550 and Differential Mixing

You may have to swap the + and - wires on one of the motors.
When operating a wheeled robot with a motor on the left and the other on the right, it is normal that the motors turn in a different direction (relative to the motor) in order to move the robot forward.

However, in the case of a boat, with both motors at the rear, pushing in the same direction, this will cause the problem you observed, unless you use a counter rotating prop on one of the motors, or just swap the wiring as described above.

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15 years 2 months ago #3932330 by DScott
Replied by DScott on topic Re:2550 and Differential Mixing
Thanks Cosma,I did check with the Minn Kota motor people and no suitable prop was available - so I switched polarity on one motor (easier than making a prop). It does function correctly and both R/C and autopilot control. I hooked the unit up to a GPS simulator and autopilot and had it run planned courses on the bench. The motors do appear to respond correctly. Thanks again.

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