I'm brand new to the forums and to drones in general. I've done lots of reading, but no actual building yet. I'd like to experiment with ArduRover with a goal being entrance into the Sparkfun AVC (I work in Boulder, so I'm close and I went as a spectator last year).
I'm particularly interested in entering the Micro class which stipulates that the car must be no larger than 10"x6"x4". I've done some research and the only decent RC car I can find that manages that size is the Team Associated RC18R (http://www.teamassociated.com/cars_and_trucks/RC18R/RTR/). Other 1/18 scales are too wide (the trucks and buggies), and smaller scales seem problematic (or they're simply too cheap and have fully integrated components).
Any feedback you have about this platform would be much appreciated. Being new, I don't want to invest fully only to discover a simple thing that makes it incompatible.
The first thing that pops into my mind is the low-profile of the ride. It looks like most rovers out there are built on larger, high-clearance platforms. I imagine the RC18R will be more bouncy and cause more noise in the sensor data, but hopefully that's something that can be worked through.
Anyway, like I said, any feedback would be awesome. I certainly don't expect to have a functioning rover in time for the 2013 AVC (full-time job, wife, 2 kids...), but I'd like to start making some progress towards the AVC goal.
This one looks close. Just under 10" long, brushless motor, but an inch too wide. I've ordered to see if the width can be reduced.
This one has silly tires, but it's the right size.
I emailed Team Associated about it a while back. Their 1/18 truck and buggy are also about an inch too wide. They said you can put the shorter arms on the Truck/buggy, but you're basically just going right back to the wheel travel of the RC18R, so you don't gain anything.
I saw the same problems in the micro dimensions; I didn't realize any 18th scale would fit. Glad you found one. The 1/24th scale cars are really small and the 1/36th scale are microscopic. I doubt they could make the ramp jump reliably with the weight of all the gear on top.
You're probably going to need stiffer springs to support added electronics weight. The weight of everything is going to be critical. How much does an ArduPilot board weigh? Can you use a GPS with a micro gps chip antenna or other lightweight antenna like a helical?
I don't believe high clearance is good. I think it's bad because it increases center of gravity and hurts cornering performance. That's why I modded my high clearance chassis for a much lower than stock ride height. It definitely cornered flatter after that.
Noise in sensor data is inevitable. The real question is at what frequencies it occurs, and whether you can filter at those frequencies without impacting signal. And if not, how can you move the frequencies so you can filter them.
Some gyros, I have found, are much more sensitive to vibration. Things may be better now. My current stance is that anything that works on a quad/heli will probably work on a rover.
I use an L3G4200D and it was fine from a noise standpoint. I had it hard-mounted to the chassis to ensure vibration was in the upper frequencies. It had an onboard low pass filter that as far as I can see from the plots must have worked.
We're also talking about AVC and rovers (but not ArduPilot, more of a roll-your-own crowd) on diyrovers google group.
Something to consider... contact patch may be too small to support high cornering speeds. Hard to know without testing.
I ran into that problem with a 1/10th scale RC car. The thing slid all over the place with the tiny little car tires versus my 1/10th stadium truck with 2.8" rims/Anaconda street tires.
Here's another 1/24th one the Losi Micro 4x4. Slightly expensive at $150, but the dimensions are good: 7"x"4"x5"
I saw some other 1/24 ones, but I don't think I saw that one. So wee, but I think the setup looks decent.
Hey Chris, did you have a chance to mess with the width on this one?
I'm looking to order an RC in the next couple of days. Currently debating between the (now discontinued) one mentioned above:
And the 4wd stadium truck (which barely fits in the 10x6)
Just an update. A few months ago I purchased a Team Associated SC18 which fits just within in the Sparkfun Micro category (technically a tad too long, but I just have to trim down bumpers). I eventually got my APM 2.6 + GPS ordered, along with a new Radio. Being a complete RC noob, it took a me a while to figure out exactly what I needed (modules and whatnot). But it all came together.
Had a trial run this weekend and it worked great!
Pretty much the only change I had to do was reverse the steering. I was amazed how plug 'n play the APM + Firmware + Mission Planner was. Great work!
I am going to get a more permanent solution for the electronics surface (sparkfun box cardboard right now...) and I also might try integrating the sonar.
I'll see you folk in a few weeks!
Nice chassis and the performance looks good.
If you have not competed in the AVC before, please be aware that the start of each heat can be deadly and you want to make sure that your chassis can suffer a direct or glancing hit from a competitor's chassis and keep on going.
From your video, I noticed that you have the same post turn overshoot across the heading towards the next waypoint that my APM equipped 1/10 scale Traxxas Slash 2WD rover suffers from when making a right or left hand turn.
A way to help mitigate the overshoot is to use active braking and slow the rover down more in the turn which helps to reduce the overshoot because the turn speed is slower or install a PX4 or Pixhawk and use EKF which totally eliminates the post turn overshoot.
I managed to stuff a PX4 and all of the associated components into a Traxxas Fiesta 1/16 Rally chassis, but it is about an inch too long even with the removal of the front foam bumper:-)
Good luck with your chassis.
TCIII ArduRover2 Developer
That's a great point. I'll have to work out some sort of roll-cage or similar. Man I wish I still had access to a machine shop...