First BW Build (Orchid Mantis)

[Lemonism]

Hey everyone,
For my first robot I'm planning on building a beetleweight, but unfortunately I don't really know what I'm doing yet, so this is my ‘help me fix my idea’ thread.
I've got a quick concept CAD done to show what kind of design I want to go for, a dustpan with a gripping claw:
mantis1.jpgmantis2.jpg
Named Orchid Mantis, same as the design I submitted for the RWRA2 Mod.
I tried to make it about the right size, based on the dimensions for the wheels using 50.8mm Fingertech snap wheels. The robot itself is 30cm wide x 34.5cm long x 4cm tall, but that’s definitely subject to change based on how much room the internal components would take up, and how much everything weighs. I made the mockup with 10mm HDPE in mind for all the sides, with a 2mm aluminium baseplate and top (on the main chassis bit, not including the dustpan).
The claw on top is pretty much a placeholder – I’m not yet sure of the best shape/materials for it, nor what should power it.
Not sure what the dustpan should be made from either, or how it should be fitted. Could I maybe use a hinge to get 0 ground clearance on it?
As far as parts go I was looking at the mini 1000rpm motors and 10a brushed ESCs from Ranglebox, as well as this radio + receiver: http://www.hobbyking.co.uk/hobbyking...x_Mode_2_.html
And this battery: http://www.hobbyking.co.uk/hobbyking...Lipo_Pack.html

So am I on the right track here?
Thanks for your time

[R9000]

Looks good! I'm a beginner too, currently building my first featherweight, so probably take stuff I say with a pinch of salt. I'd expect you'd want some kind of little linear actuator for the claw, depending on how much force you want out of the end. Although obviously as a beetleweight, you're gonna want to keep the weight down. Was it just a gripper you wanted, or is it meant to crush as well? Obviously, that'll affect what you need to make it out of and power it with. In any case, you'll want to make the arm pretty solid if you're going in with spinners, I've seen even beetleweight spinners can be quite nasty, and you don't want it getting torn off or bent straight away.

You could definitely hinge the wedge, I know quite a few 'bots do. But you'd obviously have to redesign it a little, and be careful of getting stuck on things if the floor isn't perfectly flat. Also, did you check that the TX/RX failsafes on all channels? That's an important requirement.

Best of luck, there are probably a good many others who can give more valid advice than I.

[Lemonism]

Thanks!
I was just looking at making this a gripper, working on the assumption that a crusher would be quite a lot more challenging for a newbie. To that end I want enough grip to keep an opponent on the dustpan, but I don't need enough force to crush.
I've not checked those failsafes, so I'll have to look and see exactly what that involves.

[R9000]

Yeah. With the transmitter I went for the 'buy nice or buy twice' philosophy, and got me a DX6i. It might be worth making sure it'll be suitable for any future robots you make, though it probably will.

[Phill]

For just a grip a high power servo should be enough.

www.hobbyking.co.uk/hobbyking/store/__43054__TrackStar_8482_TS_910_Digital_1_8_Truggy_ Monster_Truck_Servo_30_6kg_0_14sec_66g.html

Just as an example, but that has over 1.5kg of force at the end of a 20cm arm and it weighs 66 grams.

You don't need to worry about hinging the wedge, with the wheels near the back it will sit flush on the front of the pan.

As for the arm design, if you want you can make it a combined lifter with some kind of wedge front to get under but more importantly with the right shape it will right itself even with a relatively low degree of movement.

Not sure why you have the red wedgelets on the back.

Not sure if you have thought it through but I assume the win condition for you is to grab and then drop someone down the pit (I assume this is for kinematics and assume the pit will remain a feature) so you need to consider how your pan achieves scooping them in, holding them as they try to escape and then dumping them in a controlled manner when they won't want to. Most pans are great at the first but struggle with the second and get the opponent out by spinning.

[Lemonism]

Thanks for the feedback
@R9000, I'll be keeping a look out for a DX6i on ebay. I'm also looking at the Walkera DEVO 7E, which I saw mentioned in another thread. Same thread mentioned I'd have to update the firmware for that one, but looking around that doesn't seem difficult.
@Phill:
Servo sounds good to me
About the combined lifter, are you suggesting that the wedge + gripping claw should be connected and move as one? That doesn't sound much more difficult than just the claw, so I'll definitely consider that. Using a lifter would probably solve the 'how do I win' issue too. I'm not sure if I'd still want/need the dustpan in that case.
Now that you mention it, I'm not sure why I put those wedgelets on the back... I'll remove those

[Phill]

Here is a good illustration of what I mean

www.battlebots.com/robot/bite-force/

See how the grip arm forms a natural wedge when it closes entirely. Your arm would be something like a flat surface. Its a tiny tweek but gives you a dual use weapon.

I wasn't discouraging a pan scoop design, I personally like it, just saying you may struggle to release someone down the pit if its too long. There are a few solutions the simplest is just being fast and going from full speed to zero right next to it.

[Lemonism]

Ah, got it
Yeah that sounds both simple and worth doing. I'd like to keep the sorta curved spiked shape of the claw for the gripping part on the underside, since it's sorta the theme of the bot, but making the top into a wedge shape is definitely a good idea. Hopefully having both is doable, I don't see why it shouldn't be
What do you reckon I should go for in terms of materials for the claw?

[Lemonism]

Okay, I've made some progress
Motors from ranglebox are on their way, and I've made a new claw design:
newclaw.png
Still not sure about materials for the claw, and I imagine that might have an impact on the design.
Right now though what I'm most unsure about is the ESC. Since the 10a one from ranglebox is out of stock I'm pretty lost on what to get. I looked at the recent thread asking for alternatives, but the hobbyking one that looked like the best choice for me in that thread is also out of stock. Any guidance on what I should be looking for in alternatives would be great.
Also, I'm not sure if the servo for the claw should go through the ESC or connect straight to the receiver. I'm guessing that latter?

[daveimi]

Hi, your design is great. The sides of the dustpan will get chewed up quick by a big horizontal spinner, you may be better with just a sharp flat plate/wedge that stuff rides up onto and gets clamped. Sort of like a wedge with a clamp arm sticking up out of it. The setup will work a lot more naturally.

Sort of a bit more like this type of shape. If you look closely, there is a vertical wall at the end of the wedge to stop the horizontal spinner blades without damaging the grab/crush arm.

http://vignette4.wikia.nocookie.net/...20130920120304

[Lemonism]

Good point, sounds like a good idea. I think that would still work with the claw/lifter idea too.
One thing I was wondering about, since I can't weld I'd be bolting my robot together I assume, so I wanted to know how I could get a low ground clearance on whilst it using bolts, since they'd surely stick out from the base?

[daveimi]

It depends on the construction methods really, you could use allen head bolts with a domed bolt head so they smoothly run along the ground. You could also countersink stuff.

[Andy]

I wouldn't worry too much about side/rear ground clearance since your wheels need clearance, but at the front, if you're using a wedge, you can make it come down further than the bolts so that it scrapes the ground.

After looking back at your design I see what you mean more now, you could just use countersunk bolts for mounting the wedge near the front of the machine.

[Lemonism]

Started to buy parts, I'm planning to get this servo as recommended to me: http://www.hobbyking.co.uk/hobbyking...dproduct=43054, and a feather light lemon rx. Would this BEC be suitable to power these? http://www.hobbyking.co.uk/hobbyking...ly_6_23v_.html