Author Topic: Thinking my options through (Read 5705 times)

RedSawn · « **on:** December 19, 2012, 08:38:13 AM »

Nothing is really solid right now, but I might as well get the word out for opinions and advice.
I'm thinking of building a UK ant (0-150g) at some point. Probably when everything falls together. It is to my understanding the class sees a lot of action, so yeah.

Personal notes here:
- With a minimum budget of £150 and a surveying of the potential parts I will use on the Robot Marketplace money may not be too much of a problem, but the weight of parts is.
- I do not have real experience with metalworking, and only lower-school experience with electronics, but any equipment required should be attainable, and it may be possible that I have local sources to assist a project. I have previously cut wood and plastic (PVC I believe?) with workshop tools, powered and not.
- We have electric RC cars and a model airplane that may be possible to raid for parts, if only for the free battery and some crystals if required. Possibly wheels too but they may not be suitable for the job.
- Currently I am only referring to the Robot Marketplace for parts. Armor will be something to think about.
- I still have no bloody idea how I'm going to create the shell.

The primary idea:
A four wheeled box rammer/pusher inspired by New Blood Storm 2, or perhaps more simply, a lower profile, highly mobile Eye Poker (ya'know, from Stock AI) without the spikes. Even simpler if need be, Tornado.

And here's my would-be shopping list for it so far:
x4 30:1 Micro Geared Motor - About 9.64 grams each and about £9.79 each - http://www.robotmarketplace.com/products/0-PL1093.html
These seem to be the motor I should use for 4wd given if I go for the heavier 35:1s ( http://www.robotmarketplace.com/products/0-GM19.html ) half of the weight of the bot would be taken up by the drivetrain. It really depends on if the other components allow for it.

x4 1.75 inch Lite Flite Wheel 2pk - About 6.52 grams each, currently discounted at about £2.45 a pair - http://www.robotmarketplace.com/products/0-DAV5517.html
They seem to be a respectable choice. If the projected height of the bot is small enough I'll go for the 1.5 inch wheels ( http://www.robotmarketplace.com/products/0-DAV5515.html ) instead - drilling the axle hole shouldn't be an issue.

x4 Lite Flite Hub - 1.2 grams each and about £3.06 a pair - http://www.robotmarketplace.com/products/0-FT-LITE-HUBS.html
To attach the Lite Flites, ofcourse. Probably the most convenient because of the adhesive fixture of the wheels.

As for motor mounting I'm not sure: There's the choice of the smaller ( http://www.robotmarketplace.com/products/0-PL989.html ) and the extended bracket ( http://www.robotmarketplace.com/products/0-PL1089.html ) for these micro motors.

The total cost for the motors, wheels and hubs would be about £50 and they weigh in together at about 69.44 grams, leaving 80g and £100 for other stuff.

The backup idea:
In the case four wheel drive is not viable I could instead have a fast box 2WD rammer/pusher with a resilient front end, which particularly makes me think of All or Nothing (BBEANS) except with a ramplate instead of the rows of spikes.

Would-be shopping list for it so far:
x2 35:1 Micro Geared Motor - 15 grams each, about £11.66 each - http://www.robotmarketplace.com/products/0-GM19.html
Without the need for four motors, I can definitely use two of these heavier motors. Same again though, if the weight of the other components allows it it may be possible to go for a 1:30 COPAL ( http://www.robotmarketplace.com/products/0-COPAL30.html )
x2 1.75 inch Lite Flite Wheel 2pk - About 6.52 grams each, currently discounted at about £2.45 a pair - http://www.robotmarketplace.com/products/0-DAV5517.html
x2 Lite Flite Hub - 1.2 grams each and about £3.06 a pair - http://www.robotmarketplace.com/products/0-FT-LITE-HUBS.html
An issue here would be if I go for a caster for both sides up or just have the robot's front drag across the floor.

This setup weighs about 45.44 grams and costs about £28.33 - certainly a lot cheaper and lighter, leaving 105 grams and £121.

Building a prototype in RA2 won't be a problem. Actually drawing them up is a bit hard without all of the necessary components.
Which idea is the primary and which is the 'backup' may change as describing the backup plan as All or Nothing makes me a little fonder to see it in action.

R1885 · « **Reply #1 on:** December 19, 2012, 01:16:45 PM »

Might I recommend Botbitz gear motors? You wont have to pay the price of brand names. They're just a little bit heavier than the brand name gear motors, but way cheaper.
I approve of lite flites, but I would suggest Lectra lites. They are exactly the same as Lite Flites, but are thinner and weigh less.
The type of plastic you want to use is either UHMW or HDPE. Most US builders prefer the former, and most UK builders prefer the latter.
Crystal based radios are a dieing breed, go with a inexpensive 2.4Ghz radio.
That's my say.

RedSawn · « **Reply #2 on:** December 19, 2012, 02:13:33 PM »

It's fairly worrying that the Botbitz 1:30 motors have less than half the free-run RPM for the same weight and not much difference in price than the 1:30 gearmotor I picked out, considering speed is paramount to the design (I am also speaking like I actually have an idea what I am doing and 475 RPM may really be enough and 1000 too much). Will think about it if the projected costs are higher than expected.

Hmm, when you say the Lectra Lites are lighter, I was expecting more then 0.28 grams a wheel (though saying that it's not insignificant on something so light already). If I do have to use a 1.75 diameter wheel I'll certainly think about it, but if I can use smaller diameter wheels, the 1.5" diameter Flites mentioned are 1.7 grams lighter per wheel out of the box then the 1.75" Lectras.

Thanks for the choice of plastic, having a few alternatives to metal will help.

That's a pretty damn cheap 2.4Ghz radio. I was aware of 2.4Ghz but I mentioned the crystals just to say "I -do- have a free (if lacking) alternative."

RedSawn · « **Reply #3 on:** December 19, 2012, 04:59:08 PM »

Thanks for the tip on BotBitz and armor Vertigo. Very true with the thickness of the wheels, certainly a reason to go for the Flites over the Lectras.

RA2 prototypes! ~~In my opinion it needs more razors~~

R1885 · « **Reply #4 on:** December 19, 2012, 05:28:51 PM »

Narrow wheels have the advantage of self cleaning when they lose traction. Lite Flites and Lectra Lites have the issue of being lint rollers, trust me when I say this.
Also, you can get 1.5 inch Lectra's at finger tec robotics. They weight 4.25 grams.
If you want to build a rammer/wedge, I would suggest the 50:1 motors, not the 30:1. The reason is that you need to have very quick acceleration, like a bullet. Speed is meaningless unless you can get up to that speed quickly. This was the secret to Tornado's success.
Also, I have both a Hobby King brand radio and a Spektrum Dx5e, you have room in your budget, I would suggest the Dx5e, as it is way nicer than the Hobby King radio.

RedSawn · « **Reply #5 on:** December 19, 2012, 05:34:12 PM »

Alright, I'll look at the 50:1s on offer when I get the chance. It was a bit of an assumption to go 30:1, as while I don't know my ratios, 1000:1 is described as fine, precise movement.

Isn't there some sort of manual method to clean foam wheels?

R1885 · « **Reply #6 on:** December 19, 2012, 05:45:55 PM »

Your hands are the only good tools, the wheel is too porous to use a cleaning solution.

SKBT · « **Reply #7 on:** December 19, 2012, 08:50:54 PM »

Quote from: RedlineM203 on December 19, 2012, 05:34:12 PM

Alright, I'll look at the 50:1s on offer when I get the chance. It was a bit of an assumption to go 30:1, as while I don't know my ratios, 1000:1 is described as fine, precise movement.

Isn't there some sort of manual method to clean foam wheels?

yeah, its picking crap out of them or doing a burnout or something to spin the wheels against a non moving surface.

robot speed is simple math. for mph its (tire diameter * axle shaft speed / 336 = mph) for feet per second its (tire diameter * axel shaft speed / 240 = fps)

i'm not sure what usual uk ant speed is but 5mph is "fast" for a "us" 3lb or 1lb bot.

a "quick" robot can get up to speed in about 1 robot length.

if i was you i'd go with lite flites because they are thicker. if a chunk gets ripped out of one of them there will be more wheel left than if the same size chunk was ripped out of a lectra flite.

RedSawn · « **Reply #8 on:** December 20, 2012, 01:20:46 AM »

Quote from: SKBT on December 19, 2012, 08:50:54 PM

yeah, its picking crap out of them or doing a burnout or something to spin the wheels against a non moving surface.

robot speed is simple math. for mph its (tire diameter * axle shaft speed / 336 = mph) for feet per second its (tire diameter * axel shaft speed / 240 = fps)

i'm not sure what usual uk ant speed is but 5mph is "fast" for a "us" 3lb or 1lb bot.

a "quick" robot can get up to speed in about 1 robot length.

if i was you i'd go with lite flites because they are thicker. if a chunk gets ripped out of one of them there will be more wheel left than if the same size chunk was ripped out of a lectra flite.

That's smart thinking with the burnout. Would any reasonable surface do?

So if my calculations are correct, with the 1000 RPM micro motors and 1.75" wheels that's a theorical top speed of 5.2 mph (4.4 mph with 1.5" wheels) on something I'm going to be able to measure on a 15cm school ruler? Those are.. impressive values. I'd love to get a scale speed on that.

Another good point with the wheel thickness, I'm more inclined to go for the Lite Flites at this point.

I'm looking at the battlekits ( http://www.robotmarketplace.com/BK-BKT60.html ) and how the wheels protrude particularly out of the rear. This would solve the potential problem of being tipped onto the rear, and it would save a few grams of armor too, but I doubt it is viable with foam wheels?

RedSawn · « **Reply #9 on:** December 20, 2012, 03:20:28 AM »

If the speed and agility would be comparable to a Rotax Max kart I've experienced something with such ludicrous speed first hand x) I've raced RC cars and 80 mph karts indoors and outdoors at varying levels. Nothing with tank steering, but it's not like I'm going at it with absolutely no experience.

It is a pretty slim chance, yeah, true.

EDIT: I found out that when I was referring to 1000 RPM I was thinking of the 1050 RPM 35:1 Micro Geared motors, the big ones currently intended for the 2WD concept.
Anyway, I was looking at the 50:1 motors on the Robot Marketplace.
http://www.robotmarketplace.com/products/0-GM11A.html 56:1 Micro Geared. 7.8 grams, 480 free run RPM. Would replace the 4WD motors well; they actually weigh .4 grams less but are the same size, draw nearly the same current, almost runs at the same RPM as the 30:1s (which are actually 500 rpm) but apparently has 58% more torque. Seems like a good tradeoff if you ask me.

EDIT2: I have now also found high power versions of the 30:1 and 50:1 micro motors. The current is higher across the board but performance is significantly improved.
http://www.pololu.com/catalog/product/1093/specs 30:1
http://www.pololu.com/catalog/product/998/specs 50:1

EDIT3: I have realized I got myself confused. There are two "30:1 Micro Geared Motors" in the Robot Marketplace store. One says it does 1000 RPM and the other does not (500 RPM). I must assume one of them is the HP version but unmarked as being such.

RedSawn · « **Reply #10 on:** December 20, 2012, 11:38:15 AM »

1000:1 30:1s? Confusing x) Odd how they supposedly weigh significantly different. They're still 10 grams, shouldn't cause too many problems.

This is where I am now, a fast and agile 4WD box rammer/pusher with a tough front end to go head-on with whatever. A box will make for a simple first build.
It's probably in my best interests to go with the smaller micro motors in that case. Anyhow, here's a list of all three different powers of the 30:1 and 50:1 micros. It's hard to really say anything because every site has different readings for the capabilities of the motor, and the only thing they can agree on is the dimensions and weight.
Low Power 30:1 http://www.pololu.com/catalog/product/993/specs
Medium Power 30:1 http://www.pololu.com/catalog/product/2364/specs
High Power 30:1 http://www.pololu.com/catalog/product/1093/specs

Low Power 50:1 http://www.pololu.com/catalog/product/1098/specs
Medium Power 50:1 http://www.pololu.com/catalog/product/2365/specs
High Power 50:1 http://www.pololu.com/catalog/product/998/specs

It seems I must decide among these, baring in mind the motors, wheels and hubs will take up 69.44 grams though a bit less with 1.5" inch wheels, that I'll need to find and fit a battery in there suitable for the total current of whichever motors I use, and these choices must allow for the speed controller and shell of the bot :s I really have no idea what all of this is going to weigh.

RedSawn · « **Reply #11 on:** December 20, 2012, 12:47:15 PM »

Oh x)

Sure, it'd still go fast and it'd have the pushing power too. Now I need light enough batteries to power the motors. And a speed controller.

I was turned off from the wedge because we'd literally have the same bot! Just you have Lego wheels and whatnot.
It does bring up an interesting thought though - perhaps the front could be interchangeable, a flat plate of armor or a wedge. Hell, maybe even a scoop. If it's designed to be as simple as undoing a few screws here and there, ofcourse.

RedSawn · « **Reply #12 on:** December 20, 2012, 03:21:13 PM »

Well I'm based out of Kent, and I'll consider places as they come up.

Naturally, though it hinged on the simplicity of fixating the plate/wedge/scoop. It looks like the wedge on your bot is held on by the four large screws, which doesn't look particularly taxing to take off and put back on.

RedSawn · « **Reply #13 on:** December 20, 2012, 05:38:50 PM »

Aaaah x) Well yeah, I only need one bot for now.

So I have the drivetrain, what about the power, speed controller and whatnot?
http://www.robotmarketplace.com/products/0-SABER2X5-RC.html I'm only really aware of the Sabertooth 2X5 for a speed controller and that seems a bit heavy for UK ants/US fairys.

http://www.hobbyking.com/hobbyking/store/__11965__OrangeRx_R610_Spektrum_DSM2_6Ch_2_4Ghz_Receiver_w_Sat_Port_.html Glad to see OrangeRx was mentioned. Super lightweight 2.4 receiver compatible with Spektrum transmitters that costs just under $6? Bloody

.

EDIT: When I searched for the Spektrum Dx5e I knew it looked familiar, and lo behold, it (kinda) did. It turns out my dad's model aeroplane uses the Spektrum DX6i ( http://www.spektrumrc.com/Products/Default.aspx?ProdID=SPM6600 ). Since he basically never uses it I may of scored a free TX. There'll be no issues using it, right?

R1885 · « **Reply #14 on:** December 21, 2012, 01:26:59 PM »

I would recommend the Finger Tec ESC. They are very light weight, and very easy to use.

RedSawn · « **Reply #15 on:** December 21, 2012, 01:43:26 PM »

Convenient link since I actually had to poke around: http://www.fingertechrobotics.com/proddetail.php?prod=ft-tinyESCv2
You weren't kidding when you said those were lightweight. Would I need to do anything to them other then hook it up to everything? I.E is it combat ready out of the box or must I do something?

R1885 · « **Reply #16 on:** December 21, 2012, 02:02:20 PM »

You have to solder on both the motors and battery connectors, other wise, it's ready to go.

RedSawn · « **Reply #17 on:** December 21, 2012, 06:23:08 PM »

Quote from: Vertigo on December 21, 2012, 02:01:47 PM

The problem with them would be that you would need 2 to drive 4 motors, which then brings up the problem of mixing (which can be done on the DX6i if you're willing to mess with the settings but is still a pain in the neck).

That doesn't sound like something I can manage. Seems I'm still with the Sabertooth but isn't there a speed controller that can handle 4 motors that doesn't weigh over a tenth of my weight limit? I'm still not sure what battery I'll need but what I can tell that'll be a significant chunk of weight too, and it feels like it is adding up.

SKBT · « **Reply #18 on:** December 21, 2012, 09:57:53 PM »

go with the tiny escs. I've never been happy with the quality of the sabertooths. if you have any questions about mixing and wireing let me know.

RedSawn · « **Reply #19 on:** December 22, 2012, 06:58:57 PM »

Yeah, since I'm getting all of the technical stuff and such out of the way before I even think of buying the parts I'm going to need to know how to before I can consider the Tiny Escs, or anything for that matter.