Combat Heavyweight

Let's Make Robots Projects Showcase
1

As if my current plate wasn’t full enough, I just got it into my head that I absolutely HAD to make a battlebot.
What’s more, this bugger absolutely needs to drive me around my school campus (how cool will that look?!).
:smiling_imp:

So, I found some real nice (and cheap!) motors from SurplusCenter.
surpluscenter.com/item.asp?UID=2 … =10-2301-C
36V 2500 rpm 14.4inlbs.
ROAR!

They happen to come with a #25 11 tooth sprocket already affixed to their shafts, so I appropriately chose two #25 54 tooth sprocket and some #25 chain.
With the 6" semipneumatic tires that I’ve chosen, 500 no load rpms will still be more than fast enough for any of my purposes.
And 60inlbs of torque should be more than enough to haul me around when I sit on it.

I’ll be using 1/8"x1"x1" structural aluminum angle for the frame.
The tires and sprockets will be welded to a 1/2" steel shaft.
The tires have bearings in them, so, I’m just going to weld the bearings until they’re completely filled to ensure that the tire is tightly fixed to the shaft.
I could find real tires for it with pretty mounting hubs, but these are only 5 bucks a pop.
Then I’ll just sit both ends of the shaft in cast iron flange bearings.

For batteries, I picked up three cheap 12V 5Ah gel cells.
That way, I’ll have the ability to compete in local friendly competitions, since most don’t allow SLAs.
I’ll only get about 10 minutes of run time out of them, though, if these motor’s spec sheets are accurate.
:stuck_out_tongue:

I’m still debating on what to do for a weapon, but I think I’ve settled on pneumatic hammers.
I’ve got to borrow my brother’s, though, to see what it can do.
Does anyone happen to have one?
If so, do you think it can poke through 1/8" aluminum/steel?
I know that it does mufflers and body work, but I think those tend to be around 1/16" or less.

My main goal isn’t really to cut appart the other guy, although that would be nice, too.
Instead, I’m thinking that the vibration of the tool will be sufficient enough to damage the opponent.
If these guys are anything like their jackhammer brothers, then that should be the case.
Circuit boards are easily protected from direct physical contact, but I very much doubt if other opponents will bother to isolate their essentials from vibrational damage with rubber mounts.
Some of the most effective battlebots (Blendo ,BioHazard, and Rhino, off the top of my head) threw their opponents into the air and let gravity do all that brutal damage for them.
Rather than wasting the energy of putting the opponent into the air, I figure that it’d be more effective to create those same sort of physical shocks at a much faster rate.
:smiling_imp:

2

It might kill your chances of getting a date until you change schools. :wink:

3

Women are too expensive, anyhow.
Whoever I (eventually?) settle down with will just have to understand that they take a back seat to my robots.
:stuck_out_tongue:

Oh, here’s the schematic for the H-Bridge driver.

img296.imageshack.us/img296/5036/simplifiedmosfetgatedribx5.th.png

The above schematic just outlines what’s needed for the driver.
On my speed controller, each mosfet that you see up there is actually 4 MOSFETs in parallel, for a total of 16 in each bridge.
I’ve also left out all those passives that keep the bridge from dying (like the transient voltage supressors, brownout capacitor, base limiting resistors, etc.).

I’m using optoisolators for simplicity’s sake, because I’m not a transistor guru.
Optos have never failed me.
Simple transistors would probably be a direct replacement, in this circuit, though.
Basically, the bottom two FETs just get 12V stuck right into them.
The top two get the motor battery voltage (30V in this case) plus 12V stuck into them.
And there’s also an optoisolator on each gate to connect it to ground.

All FETs have a slight capacitance, so when you take 12V off of them, they stay on for a while until those volties dissipate.
Grounding the FET’s gate turns it off “imediately”.
The 10 ohm resistor needs to be there to keep the transistor from passing a brief infinite current and theoretically frying itself.
It might be OK to do without it, but I’d rather be a bit safe.
The upper FET gates will release 42V / 10 Ohms = 4.2A, when grounded.
That’s well above what an optoisolator can do, but with a gate capacitance of only a handfull of nanoFarads, that 4.2A will shoot through so quickly that the optoisolator should not heat up at all.
It’s necessary to use seperate control lines for grounding the FETs’ gates because if I were to, say, ground the lower right gate when turning on the lower left, I’d have shoot-through.
The 10 ohm resistance gives an RC constant of about 50ns or so, which means the lower right FET would be at least partially conducting during that extra time.

I’m gonna go start building this circuit now, but I don’t think I’ll get it finished today.
When I have more free time, I’ll draw up the complete speed controller circuit in case any of you guys want to play with your own.
I’m “supposed” to be writing an Art paper, this weekend…
:wink:

4

Well, as it turns out, I can’t find my bucket o’ optoisolators, so I haven’t been able to physically test the circuit.
I did test the circuit with MultiSIM8, a pretty powerful circuit simulation tool that my school uses.
It worked well for switching a simulated 50V 100A load up until I reached high frequencies around 30kHz.
I’ll only be using it at 1kHz or under, anyhow, so all systems are go.
I’ll have to see if I can get my teacher to loan me a handful of optos.
:laughing:

So, what I got done was this:
img396.imageshack.us/img396/2833/windtunnelbo3.th.jpg
As you can see, I slaved for about five minutes to bolt these together.

I did get a lot done with the robot itself, though:
img396.imageshack.us/img396/3751/witfrontzf7.th.jpg
Note the penny placed on the motor to the left, for size reference.
Those motors are HUGE!
And boy, do they PURRRRRRRRRRR!

Oh, yea, you might notice that things are a bit crooked.
No worries, though.
The wheels are attached (until tomorrow) on only one side by a bearing.
That bearing is self aligning, so it can swivel about 5-10 degrees or so in every direction, which is why the wheels seem a bit crooked.
Tomorrow, I’ll be welding together the struts to mount the other sides of the wheels to.
Then I’ll have to whack on some casters and actually weld the motors in place (they’re just laying there in that picture).
I could bolt them on, but I’m lazy and I’ve really been enjoying how fast welding gets done, as compared to the slow, imperfect, and less strong process of drilling and bolting.
After that, I need to strap on the #25 chain (go ahead and tell me that #25 isn’t strong enough :stuck_out_tongue:).

img394.imageshack.us/img394/5601/witisometricqs9.th.jpg
An isometric view.
You can see the flange bearings that I’ve used.
They’re rather beefy.
:wink:

img371.imageshack.us/img371/8472/witdrivealignmentpf9.th.jpg
Note the cat.
She’s rather annoying.
I almost welded her to my bot, yesterday.
:stuck_out_tongue:

I’m going to be strapping a FIRST controller onto it when the base is done, so the kids at my local FIRST team can practice driving on my bot.
This bugger will be REAAAALLLLLYYYYY twichy, much more torqy than they’re used to, and very fast, so it’ll give them good practice with joystick finess, which they drastically need.

5

Oh, almost forgot…
The batteries that I got were a lot smaller than I’d thought.
I highly doubt if I’ll get any run time out of them, at all.
For now, I might just run the motors on a cheap 12V car battery.
It’ll be slower and less powerful, but I gave it a try, already, and it’s plenty enough to pull this behemoth around.
When I can afford it, I’ll buy a deep cycle 12V battery.
Right now, this guy is already 33 lbs, and it’s less than half finished

Then I’ll buy 3 1:2 transformers and arrange them in a 1:6 stepup combination that shares the power across each (huge wattage transformers are really expensive).
Speaking of that, anyone know a good place for surplus transformers?
I’ll use a MOSFET to chop the 12V coming in with a 100kHz frequency at 50% duty cycle.
That 6 effective volts goes into the transformers and comes out as 36 effective volts.

Then, that goes into my speed controller which might be operating at only a couple hundred Hz or so, so the 100kHz noise that it’ll be switching probably won’t be a problem.
Any electronic gurus see a problem with that?
I’m hoping that the 72V peak (36V effective) cominging out of the transformers won’t be a problem, considering that I’m building the ESC for around a 50-60V overall rating.
Now that I’ve gotten rid of the driver (fried it :stuck_out_tongue:) and am making my own, the only thing that limits it to 50-60V are the caps, so I can replace those, if need be.
Or, do you guys think I really need to rectify it back to a purely DC signal?

6

You know, they say… “Curiosity kills a cat” :laughing:

I know what you mean. My daughter’s cat jumps up on the desk and stands right in front of the monitor, usually wanting something.

7

ill battle your Combat Heavyweight with my future secret rover project (that you know about btw the way) i think the bets on me, as long at me can battle on some ice that is just thick enoguh to support the weight of my bot but not yours, we on? :laughing:

btw, llooks good, keep up the good work :smiley:

8

Thanks, guys.
:slight_smile:

I almost finished the welding today, but I ran out of stainless steel welding wire.
After I pick that up, I’ll only have the motors left to weld.
I should probably redo one of the casters, too, as I placed it a bit higher than it should be.

After some minor realignments, I’ll be ready to head to town on the electronics, full force.
On Tuesday night, I’ll be going down to the South Jersey Robotics Group meeting, so I hope to have all the mechanics working right by then, so I can show her off.

Oh, not sure if I mentioned it before, but her name is, “Where It Counts”.
I plan to engrave that on the body armor that I’ll eventually be plating her with.
And yes, she’s female.
:wink:

9

aren’t robots more amazing when we think of them as female??? :smiley: