Control box pulled in a cart

Frustrated that my mower/ rover would not track waypoints I put the control box in a fabric cart and just watched the icon in QGC. Walked in an S pattern and the screen icon seemed to track the cart very well. The same system on a large walk behind hydro just wanders around aimlessly. I see others running modified hydros on this site. Am I expecting too much from this large machine and the 8MN device?

The M8N is a decent GPS for basic positioning, but it is only ever going to be accurate to 1-2 meters. You’ll need an RTK capable GPS for any serious mowing/agricultural task, in my opinion.

Regardless of GPS precision, you still need to tune the rate and nav controllers for your vehicle. You should be able to achieve at least proof-of-concept results with decent path tracking.

If you would permit me one more question: is the linear servo I’m using to drive the hydros’ quick enough to make good use of the RTK? The near $1K RTK price makes me ask. What do you use to drive your hydros?

Hey Mitch - Depends on the linear servos you are using. My first build used linear servos that had 25 lbs force and moved about 1.2"/Sec. They worked great but during the final build, I realized that the high force wasn’t needed and used regular HD servos instead for cost savings. There are many flavors of linear servos so you can likely make it work. Really depends on what force you need to move your control lever. I am tied directly into the final lever on the Hydro-Gear (brand) drives which need very little force and eliminates all of the linkage slop that was present from normal wear on the older ExMark mower.

As to the RTK necessity, agree completely with Yuri. You will need some flavor of RTK for mowing applications. No other way to get the accuracy required. And plan on spending a good bit of time tuning your rig. Both are key. For reference, on straight runs I’m usually seeing cross track errors between -0.02 and +0.02 meters @ 5 mph.

And depending on your situation, you can get RTK for less than $1K. I’m using a Sparkfun F9P GPS board for a base along with a good antenna and good coax mounted on the roof of the shop. Mission Planner handles sending corrections to the rover over the telemetry link. Total RTK system ~$400. Likely cheaper solutions now. Good Luck!

To echo Steve, there are too many variables to directly answer your question about your drive system.

I’ll give a very subjective answer:

Drive around in manual mode. If you can maneuver about as quickly/easily as if you were riding on it and directly controlling it, then you are in good shape. If control is sluggish and leaves you wanting, then you should consider a faster drive mechanism.

Thanks to you both for your time! Looks like some reading on RTK is in order.