Category: MAVRIC

Last week, I was working on cleaning up some wiring, specifically the wiring providing power to the wheel motors controllers. When it was originally done, we weren’t sure if the length would be changing, so we left them long (about an extra foot on each cable). This meant that they were hanging down under the rover and were generally in the way. We now know that we are not changing the suspension before competition, so I decided to fix the length. It looks much nicer now.

Jump to Saturday, we go to start a test drive, power on the rover and hear some clicking/popping sounds. We check all the LEDs and one of the motor controllers is not working. A review of the wiring on the left side of the rover (right in above image) showed that I had plugged a pair of wires in backwards. Now, I’m usually a careful guy, and I did actually attempt to check the wires, I just did so incorrectly (clearly).

Further diagnostics on the motor controller showed that the internal microcontroller was fine, but all the power transistors for the H-bridge were fried. Thankfully, we had spares ordered already.

Events like this are why I usually opt for polarized, grouped connectors for my cables (XT60s are amazing) but sometimes there are external constraints in place. We have a very tight window for those cables to fit through, and it is not possible to push a solid multiple-pin power connector through the window. We are using bullet terminals because they are very close to the size of the wire, and allow the wires to be pushed through individually.

This has reinforced my opinion on polarized connectors as a necessity, and served as an excellent reminder to always check your new/modified thoroughly connections before activating a system. It is especially important to identify things that you are doing in a riskier manner, and check them extra carefully. Know your risks, and watch them closely.

 

More MAVRIC! Today we had another test drive, and got some good footage (some of it is below). We haven’t edited it together or anything yet though. We took the rover out to the Frederiksen Court area north of campus to get some open space. We were able to get up to 0.2 miles (measured with some GPS pins on a phone) with some small buildings in the way before the connection dropped below acceptable levels. We were able to recover the rover from that distance using the antennas, the cameras were just too laggy to drive very well or operate the arm (not currently attached).

As mentioned, we did a range test, with the first sign of degradation at ~0.1 mi, and the rover becoming unusable at ~0.2 mi. This is a little concerning, but workable for most events at competition. We also did some testing of the suspension’s ability to handle rough surfaces, large bumps and hills. The rover was able to climb over curbs (with a little practice) and remained stable over washboard-type terrain (the 6 wheels help out there). The rover was also able to maneuver on uneven ground at significant angles, though it could not climb steep hills. When driving, the camera mast shakes back and forth, even without the main camera mount attached and may need reinforcement. See the videos below for examples (links because I can’t host videos here, sorry).

Washboard: https://iastate.box.com/s/u1s6bgy23gspb59n9qvf1u7amnplxku7

Bigger Bumps: https://iastate.box.com/s/9hk372vl0fm39629aco75z09jwiqpm0d

Angled Terrain: https://iastate.box.com/s/jbldn017uwto6jfl4lh8ngg4cs5f3dxi

Parking Lot Driving (curb at the end): https://iastate.box.com/s/5h1jv6h9ey0yxjjingovo30o6t4byfnu

 

Nothing too big, we had the M2I Kickoff on Tuesday, so hopefully we will be getting some new members coming in. We have several returning members (almost all of the electrical team came back, and most of mechanical). Unfortunately, we took a pretty big hit on science – the team responsible for the soil analysis and scientific presentation. We have 1-2 returning members. If anyone has experience/interest or contacts with experience/interest in soil analysis (focusing on factors that indicate the possibility of life) please contact me.

That’s about it for now, I hope to post more photos and videos eventually. We can’t do test dives right now because the key (a little part that forces the motor shaft and the wheel to rotate together) is missing, and an Allen wrench broke off in a screw. We should have that fixed quickly once the machining lab is open next week.