Comments

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  Antonie Kruger February 16, 2014 at 2:31am

  Thanks Michael - do you think it would be possible to implement policing/managing of the MANUAL mode inputs to soften the outputs as AUTO would do?
• MikeRover February 16, 2014 at 2:15am

  Antoine, I forgot there's also a throttle ramp rate in APM:Rover you can use. That should be easier than any kind of filter and you can then do your necessary settings on the Sabertooth with DIP switches only.

   

  The only downside is that the throttle ramp in APM only applies to AUTO mode - you can still hurt the motors in MANUAL mode. 
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  Antonie Kruger February 16, 2014 at 2:08am

  Hi Michael, thanks - Ramp Time is what I'm after.

  It just occurred to me that applying a low pass filter on the output lines with a adjustable cutoff rate will have the desired effect. The lower the cutoff, the less rapid the change in output.
• MikeRover February 16, 2014 at 1:42am

  @Bruce, the current ratings are at 25C, and they de-rate from there. From the specs, it looks like the motors shouldn't pull more than 7A, but if your chassis is enclosed, or you're somewhere where the ambient temperature is 30+C, the extra margin may be useful. I'd assume Thomas went for the 25s for a reason, unless he had it lying around.

   

  @Antoine, the Sabertooth can do ramping internally, but you need the DEScribe software and DELink USB converter to set it.  I don't know if you can substitute another USB/serial converter.

   

  "Ramp Time

  This is the time the driver takes to go from full reverse to full forward or vice versa. High ramp rates give a slower-acceleration, softer feel."
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  Antonie Kruger February 16, 2014 at 1:21am

  HI Guys, thanks TC3, great job. Would you be porting the skid steer implementation to the APM2 boards? I have a few questions that I need some help with. I have a wild thumper 6wd chassis with the wild thumper controller board. I fitted my apm2 board with telemetry.

  Q1. When the controller is instructed to apply 50+% speed to the motors from 0, a lot of stress is placed on the gearboxes in the motors. It is not long before the drive gear in the gearbox strips. Would it be possible to manage the application of power to the motors over a longer period. I'm not sure if I'm explaining this right. The effect I'm after is : When I instruct 100% power forward the controller should not apply 100% immediately. It should accelerate from 0 to 100% over a time period to reduce the torque forces on the gearboxes to lengthen the life of the hardware.

  Q2. Does anybody know of better quality motors for this chassis or just gearboxes. The stock boxes sucks. Seems like the gears are mild steel or cast iron. Real cheap crap.

  Q3. Can the APM2 rover software take a NMEA string from a serial port for navigation. The reason for asking is that I use a robotic survey instrument to lock onto a 360 prism mounted on the rover. From here I transmit the coordinate to a FEZ Cerb40 netmf board that translates the coordinate into the needed NMEA strings, alternatively using a RTK GNSS receiver mounted on the rover to feed the needed NMEA strings to the controller.

  Thanks,

  Antonie
• Bruce D. Sidlinger February 16, 2014 at 12:39am

  Beautiful, and I was just tonight ordering that chassis, the high gear ratio (low speed) version. Question, would this controller have been enough, do you think? http://www.dimensionengineering.com/products/sabertooth2x12rc
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  Gary McCray February 15, 2014 at 9:02pm

  Really clean install TC3 how do you like Wild Thumper?
• Admin

  Thomas J Coyle III February 11, 2014 at 4:39pm

  Hi All,

  I would like to announce that I have successfully implemented the Pixhawk firmware skid steering function on a 6WD Wild Thumper chassis using a Sabertooth 2X25 motor controller setup as two independent motor controllers, one for each side of the Thumper chassis.

  Here are some pictures of the Thumper and its Pixhawk subchassis:

  

  I raised the GPS/Compass module above the subchassis using a 2.5" high platform to mitigate the effects of the front motors' electromagnetic field. I got the compass deviation under power to go from an offset of ~40 deg to ~2 - 3 deg using the raised platform.

  Regards,

  TCIII ArduRover2 Developer
• MikeRover February 6, 2014 at 5:32pm

  I've copied my AUTO mode questions to the [url=http://ardupilot.com/forum/viewtopic.php?f=26&t=6024]APM forum[/url]. Keen to hear others' suggestions.

   

   
• 

  Gary McCray February 5, 2014 at 5:21pm

  Hi Tom,

  I haven't installed telemetry yet, but might be a good idea to do so soon, sort of taking this one one step at a time.

  I have been fully charged though and limiting total running time to less than 8 minutes though with plenty of battery when I get back.

  I will eventually replace with serious LiPo, but using stock NiMH for now.

  However, you are right it could be power surge causing resulting short term voltage drop, I will look at logs and see what they show, should be obvious there.

  Even on uneventful runs.

  And of course, unlike APM, PX4 won't reboot in a useful fashion because you can't rearm possibly it might be worth removing (or modifying) this "safety" feature for this particular use.

  It is getting better, now normally fails to Hold and haven't had another runaway - - - yet.

  Turning down the Cruise speed probably has the bonus that it doesn't accelerate as hard so pulling less current and lowering voltage less - reducing likelihood of brownout.

  Definitely do not want to do this in a small yard surrounded by 100'+ pine trees and a 2 story house though - multipath seriously screws it up on auto.

  (You can see it wandering all over the place on MP even when it is sitting still.)

  Not a problem though I already knew that.

  It's getting there.

  Thanks again,

  Gary