chassis for a pixhawk autopilot

[Serg]

I am looking into building a rover (http://rover.ardupilot.com/) with a pixhawk autopilot (https://store.3dr.com/products/3dr-pixhawk) but the chassis they usually employ are a bit too weak, and so I am considering your 4WD All Terrain Robot Platform – IG32 SB (TP-132-032)
as a sturdier and more load bearing base. It will need to carry ~5-6lb of load with a speed of ~5-7 mph over mostly flat fields (grass/packed sand), so I am thinking about using “IG32P 24VDC 265 RPM Gear Motor with Encoder” with the 6″ wheels for that.
It looks like pixhawk supports Spektrum DSM-X receivers so for manual control “Spektrum DSMX DX6i Transmitter with AR6210 Receiver” seems like a working option.
Now it gets more complicated, as for output they have throttle and steering, so in order to control the motors they recommend using Sabertooth or RoboClaw. one of the options available here is RoboteQ controller with encoder inputs. Would it work with the motors I mentioned above, and would there be a noticeable advantage in using the RoboteQ with encoded motors vs. Sabertooth with the regular ones?
I would also appreciate any other suggestions/pointers/tutorials, and be grateful if you see any flaws in my thinking.
Serg

[SuperDroid]

Any of our chassis will work with the Pixhawk or Ardupilot. We have used both of them several times. Its very easy setup. A motor controller with mixing is best, but you can set it up with differential steering too. If the motor controller has mixing, such as the Sabertooth you just send the RC output of the Pixhawk to S1 and S2 for throttle and steering. You hook up the output of elevator and aileron to the inputs of the Pixhawk (i believe 1 and 3). There are tons of support topics/forums online for doing this step by step and what IO to hook up to, etc.

5-7mph is a fast pace for skid steer. Our robots use skid steer/differential steering. ie the wheels have to skid to turn. you slow one side of the robot with relation to the other or even reverse one side. This allows the robot to turn on its own axis and makes the chassis simpler. This is unlike the conventional steering system like on cars, etc. Since the wheels must skid to turn, it takes a lot of power. if the wheels don’t skid, the robot will not turn. The more weight, the harder it its break traction and skid/turn. So typically we use higher torque motors and gear boxes as opposed to higher speed motors with less torque. You can go to bigger motors, but the cost goes up and you need bigger batteries and bigger chassis, which is more weight, which is harder to turn. All our robots are listed here.

All said the only robot we offer that is close to that speed is our IG52 wheeled chassis. We have a couple different ones. 4WD All Terrain Robot with Custom Length – IG52 SB this one is direct drive, so its not as heavy duty, but does not have any gear reduction. You have to supply your own base, but we can cut and bend a sheet of aluminum if you wish. The other option is 4WD All Terrain Heavy Duty Robot Platform – IG52 DB. Its a heavier duty chassis and has a gear reduction to it so it will be slower with the same RPM motors. Nothing else is needed with this chassis and it will handle a lot more weight and abuse. You can pick the fastest gear ratio and as long as you don’t load it up with a bunch of weight you will come close to your speed requirements. We have a speed calculator here. remember to input the gear ratio of 14:21 (0.67) for the heavy duty chassis and 285 RPM (for the faster motors). For the direct drive chassis you would use a gear reduction of 1 and 285 RPM.

[Serg]

thanks!
the TP-132-032 with 265 RPM motors would drive up to 7.6km/h which should be sufficient for my needs. (should have said 5-7 kilometers per hour, not mile per hour)
the scenario I have in mind is very close to the lawn mower, and it doesn’t have to turn 180 degrees when moving to the next lane – just do an s-curve maneuver to shift ~1.5 feet orthogonally before going back. I guess if it were to slow down before that it would be fine with me – not sure if the pixhawk would support it though.
Serg

[Author]

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