Beach Detecting Rover project

[fixstuff]

chassis updates

Well, I made a lot of progress over the past week on the Rover. I have gotten most of the chassis complete. I have stripped out and cleaned up the old enclosures I'm going to use. I still have a couple pieces to add to the chassis and seal up and paint the enclosures.

I also started work on the Propeller sensor boards. First section is working fine, which is the SHT11 temperature/humidity sensor. I'll add the other sensors this weekend to complete that board.

Still working on some ideas for the coils. I haven't started on the jib crane yet, so I'm still trying to decide how I want the coils to look. I've been considering a coil array also of some sort. Has there been any work using a large transmit coil, and a bunch of smaller receive coils with individual receiver circuits set up for different windows? I'm really not wanting a large moving arm on this if I can figure out a good way for the coils. Maybe a dual large coil array with a large coil on each side of the rover out from the side... Any thoughts on that?

I still want to build a custom detector of some sort. Any ideas or suggestions is appreciated. I will be trying out a blanket coil as well. I'm still looking for a nice non-metallic grass seeder or similar assembly I can hack to make that. If anyone has seen something that would work for that, please send a link or something. I'd also be willing to buy a blanket coil from someone if they have made one that works. I'm willing to make one, but making one will have to wait till late, and I want to make sure I have one ready due to time constraints.

Another thing. I'd be more than willing to test anyone's detector design and coil design on this system. Once it's running, it might be helpful to quantify detector performance on a common platform.

Anyways, here are some recent pictures on the build.

[Farside]

Hi fixstuff,

I'm looking at your build and thinking that it might not fit in the trunk of your car

Seriously, I'm thinking about the weight. Have you done any rough calcs with regard to this?

The reason I ask is that the rover might get stuck in dry sand and may even sink in soft wet sand (which happens with cars and trucks all the time)

[fixstuff]

weight

Nope. Won't fit in truck of car. It is intended for a trailer being towed, or partial disassembly. I am designing everything to be taken apart into subassemblies. Wheels will be attached to quick disconnect collars. Frame comes apart into two pieces. Enclosures are removable. Generator is attached by strap. Connections everywhere are removable, etc.etc.

I fully intend to ship this via trailer. Think 4 wheeler. It wont fit it trunk. That is unless you have a really big trunk . Same with this rover. If I make the rover small enough to fit in a trunk, it wouldn't be big enough to support the detector arm, or do all the stuff I want to do with it (like tow giant coil arrays).

The motors and wheels I am using are freaking huge. If I made the rover smaller, they wouldn't work. The motors are each capable of 200lbs of weight on each wheel. 4 wheels gives me 800lbs. I don't expect this rover to weigh that much. I'm looking at the 400-500lb range. That gives me 100-125lbs per wheel. I'm thinking that this is similar to a large person's foot pressure. Granted, a human stride is different than a wheeled movement, but I'm hoping that the rover will move similarly. I will just have to see. I completely agree that loose beach sand will be very bad for the wheels I have. I intend to use balloon beach tires if I want to use this in that environment.

My first use of this rover will be normal dirt and desert scrub area. I won't be in loose sand in those areas.

If I do end up in sand, the following rules will be working in my favor: I will keep my tire pressure as low as I can and still maintain the tires. The motors will have very long accel and decel cycles, to keep spinning from happening.

I have calculated the rover ground pressure to be in the 10-15psi range. By increasing my tire surface (i.e lowering tire pressure), I can lower that even more. A human walking is in the 8psi range, so I'm figuring some beach sand will be fine, some won't.

I used these sites for reference:

http://en.wikipedia.org/wiki/Ground_pressure

http://www.dirtopia.com/wiki/How_to_Drive_in_the_Sand

Four wheel drive will also help. Although I don't have encoders on the driven wheels, using an encoder per wheel could give me some anti-slip capability.

Anyways. Hope this helps clear up some of that. Ultimately, we'll have to see how it does in real tests, but I'm hopeful.

[fixstuff]

updates

Hello all,

Here is a new pic of the chassis and controls/amplifier enclosures. Doesn't look like much but it was a solid weekend of work getting that knocked out.

Next steps are wheel mount brackets, knocking out fan/inlet holes in enclosures, and starting on the coil sweep arm.

[fixstuff]

new updates

Here is another picture of the rover in progress. Right now the wheels are mounted, the chassis is almost complete. Only 1 more piece to mount and the chassis will be finished (other than cleanup or painting).

After that, the generator will be mounted next, along with the batteries, and all of the electronics parts inside the enclosures.

[fixstuff]

updated site for project

Hi all,

I created a blog site to document the rover a little better. I will still post to the Geotech forum with major updates, but I will keep files, video links pictures etc. on the blog, since it can be updated when changes occur, etc.

I haven't done this before, but there are some useful stuff on the blog such as links to the websites for some of the software and hardware I'm using, a download section, and videos of the project on the bottom.

Another thing that I think is nice is the translate feature on the side. Since there are a lot of countries represented on the forum, I thought this would be a good feature.

Tell me what you think!

http://fixstuff-thots.blogspot.com/

[Farside]

Nice job as always fixstuff!
Does that surf coil actually work or is it for "test purposes" only?

[fixstuff]

It works fine actually. I could detect my gold ring about 6 or 7 inches with it, but that's as far as I tested with that.

[fixstuff]

More updates to rover

I added some more hardware to the rover. Here are some pictures of the progress..

link to the build detailing everything...

http://fixstuff-thots.blogspot.com/

[jon-ecm]

Awesome work!

This is looking awesome man! Such professional work!
Can't wait for the next update! Be sure and keep us posted...

Jon

[Farside]

Yes very impressive Fixstuff. This thing is gonna last longer than my personal vehicle!

Considering this is a beach rover, have you thought about how you'll keep the wind blown sand and salt out of that box? I noticed some pretty big venting holes. there is some pretty cool open cell foam around that can help but sand gets into absolutely everything.

It never ceases to amaze me how it does that

I bookmarked your blog BTW

Edit: Come to think of it. That is a pretty big metal box which means it's also a pretty big heat sink...

[Qiaozhi]

I added some more hardware to the rover. Here are some pictures of the progress..

link to the build detailing everything...

http://fixstuff-thots.blogspot.com/

You're making rapid progress with this project.

I'm interested to see how you plan to mount the coil(s). Not only will the rover itself make a rather large target for the detector, but the electrical interference might be a major problem. Watching with interest ...

[der_fisherman]

It will, but whit break torque not exceeding one in normal (drive) condition, more or less, may not be sufficient in some situations. Heavy machine can be accelerated slowly, but if it needs to stop rapidly, significant (kinetic) energy must be wasted somewhere quickly, then, without some mechanical means, motor itself will not be able to do that, not only shorted but even using reverse drive (drive power control is current limited).

12K$ for this project, without Ebay, is very optimistic!

As Davor suggested, shorting or partially shorting the motor (after removing power!) will make it slow down very fast. It may then just creep if the load is large and the slope is steep.
Till you have tried it you will not believe just how effective it can work....
My suggestion is to use a suitably rated number of resistors as you probably don't need an "emergency stop" function!!
Best of luck
regards
Andy
PS Its also how "good" hand tools are stopped when switched off, almost instantly, with a short across the motor.
By the way this works on almost all DC motors (I don't know of one personally that does not work in this way!) and all AC motors that I have ever seen....

[fixstuff]

@der_fisherman: I've got brakes on all the motors (except one ), Looking at how big this thing is, I originally intended to keep the brake energized all the time (disengaged), but now I'm thinking when it's not actually moving, I will turn the brake off (hard stop). I also will have the brakes tied to the ESTOP circuit. If I lose comms or hit the ESTOP button, it will shut off power to the motors instantly. Also, all of the motor drive boards have shorting brake functionality which I will use also.

@Qiaozhi: If you notice the arm I have so far, its an aluminum tube. To finish it, I will mount a wooden dowel or PVC tube into the aluminum tube, secure it, and have the coil also on a wooden or PVC dowel down to the ground. I will have an adjustment at the insertion point for the dowel into the tube, and I will have it extend WAY out from the rover so I don't pick up a metal signature. I'm hoping about 3 or 4 ft will be enough. During scanning, I will have all motors off, with the exception of the arm rotation motor, and the arm extension motor only on during indexes. So hopefully, motor noise will be vastly minimized. I will try scanning with the rover moving just to try it, but if I do that I will swap out to a huge square coil, say 5ft or wider, and not sweep with it, just operate in a fixed position.

@Farside: All the holes are now plugged. Any holes I add now will be IP67 water splash resistant. I am going to "try" to see how warm it gets with the box closed up and no ventilation. The base of the box will be bolted down flush to the treadplate, and should provide a pretty good heatsink. Each power supply has a fan mounted on it, so the air inside the box should be stirred up quite a bit. I've run enclosures like that before, and they do get hot, but I'll have to see. I might even plumb up the box with a self-contained water cooler system. I'll have temp monitoring on both boxes to make sure I don't fry anything also.

@All: Thanks for all the positive feedback! I'm trying to build it to last, I'm sure the workmanship could be better, but man it's hard to build in metal on this scale.

[6666]

With the sweep arm, you will basically need the coil as close to the ground as possible
has the arm got any "give" in it, as the rover bounces along the uneven and pot holed beach
you have the possibility of the coil hitting the ground and bending / damaging the arm.