Thinking my options through

[MikeNCR]

With mixing, you can either do it on the transmitter itself or get a small plug in mixer that can be put in the robot itself.


DX6i mixing:
Lighter robot weight
Lower top speed due to how the mixing works


Onboard mixing:
Higher robot weight
Faster drive speed


I've used this one in several robots and it works great- http://www.robotmarketplace.com/products/0-DGEVMXR.html
The fingertech one works as well, but it doesn't failsafe properly, so it may not be legal if the rules require a full drive system failsafe.

[RedSawn]

Sounds like it'll be onboard mixing. Surely can't be that much weight difference, right?

I'm curious as to how these motors will control now. I've been looking for videos of other 150g bots and all I can seemingly find is servo drive, unless I am mistaken about other drive motors at this level.

EDIT: I'm eying this battery as a power source. http://www.modellbauuk.com/e-flite-200mah-battery-for-mig-306-p.asp Light, within the voltage range of the motors and will theorically last 30 minutes in use (400ma current total from the four motors, maybe it'll be more on a bigger voltage so maybe I need a 350maH). I can't find a better option.
EDIT2: http://www.google.co.uk/shopping/product/17294855120760941065?q=7.4v%20300mah%20lipo%20battery&ie=UTF-8&oe=UTF-8&hl=en&client=safari&sa=X&ei=ekzaUIOiNoWJ0AX0koEg&ved=0CDcQ8wIwAA#hsec:overview 300maH 7.4v E-Flite in the case of needing a tad higher capacity.

[SKBT]

almost no US fairyweights (150g) use servos for drive.

your smaller battery should be fine.

[RedSawn]

Sure, I just can't find any videos of 150g robots that don't look like they use servo motors. I am of the mind that the videos I am finding are of older competitions and robots where the micro geared motors were not as widely used (Apparently).

My shopping list so far, then:
x4 50:1 Micro Geared Motor HP - http://www.pololu.com/catalog/product/998/specs
x4 Lite Flite Wheel 2pk (1.5 inch or 1.75 inch diameter depending on robot height) - http://www.robotmarketplace.com/products/0-DAV5517.html or http://www.robotmarketplace.com/products/0-DAV5515.html
x4 Lite Flite Hub - http://www.robotmarketplace.com/products/0-FT-LITE-HUBS.html
x4 Micro Metal Gearmotor Bracket - http://www.robotmarketplace.com/products/0-PL989.html
x2 tinyESC v2 Speed Controller - http://www.fingertechrobotics.com/proddetail.php?prod=ft-tinyESCv2
7.4v E-Flite 200mAh Battery - http://www.modellbauuk.com/e-flite-200mah-battery-for-mig-306-p.asp
All in all about £110 and 93~96 grams. Seems like quite a lot of weight to have left, though this doesn't include the body.

To consider:
OrangeRx R610 Spektrum DSM2 6Ch 2.4Ghz Receiver - http://www.hobbyking.com/hobbyking/store/__11965__OrangeRx_R610_Spektrum_DSM2_6Ch_2_4Ghz_Receiver_w_Sat_Port_.html
500x250mm sheet of HDPE (Not sure about thickness) - http://www.directplasticsonline.co.uk/HDPESheet/Natural/

Things I already have:
Spektrum DX6i TX
Spektrum Dx5e TX (Yes, turns out my dad has one of these too, and I assume the included RX would be somewhere too)

[haz]

some modern 150g uk antweights.

http://robotwars101.org/forum/ this might be a helpful place.

[RedSawn]

Been thinking about this again for the last week or so. Sometimes you just get inspired and you can't think of doing something another way.
I want to make a 150g Madd, I think it's possible depending on what I do.



(The wedgemaker and DS tooth are only there for extra damage and RA2 flipping stability, it's really all about the spike)

The drive should be fine to keep on the shopping list, as well as the battery:
x4 50:1 Micro Geared Motor HP - http://www.pololu.com/catalog/product/998/specs
x4 1.5 inch diameter Lite Flite Wheel 2pk - http://www.robotmarketplace.com/products/0-DAV5515.html (It's pretty clear to me that I won't struggle keeping the shell under 3.5 centimetres tall while fitting the parts in)
x4 Lite Flite Hub - http://www.robotmarketplace.com/products/0-FT-LITE-HUBS.html
x4 Micro Metal Gearmotor Bracket - http://www.robotmarketplace.com/products/0-PL989.html
7.4v E-Flite 200mAh Battery - http://www.modellbauuk.com/e-flite-200mah-battery-for-mig-306-p.asp

The weapon is where it gets interesting though - unlike in RA2 I have the option of using a servo to power the arm, which can be lowered/raised to get under the opponent either way up and flip with, or kept in a neutral position for a ramming spear. With mixing the drive could be entirely controlled by the left stick, and the servo the right. Regardless the inclusion of a weapon on a motor means the two TinyESCs won't do it.

Another point is that 99% of the Micro (5-10g) servos are only rated at the most 6V while I have the 7.4V battery. This is assuming these servos (Be it as light as 6g or the 9g ones) have the power to lift or flip 150g opponents with the end of a 4 or 5 cm spike. With torques from 800g/cm to 2.2kg/cm it's hard for a lamen not to make a case. If the servo has a thickness of 9mm like some of the ones I've seen it may be possible to fit it to the front end, between the motor and the front of the bot, without removing the slots for the front wheels to stick out (It would help if the servo was smaller lengthways in that case too). I've also tried doing a diagram of a layout where the servo goes under (or over) one of the drive motors, but this is really less ideal as it complicates construction that much more. This ofcourse isn't RA2, where the parts inside the chassis are fixated in time and space.

The question is if this is doable. The current shopping list weighs in at roughly 75 grams (I hope I weighed everything because that's lighter then I thought for just trading out the 1.75 inch Flites and not including the TinyESCs), not counting the brackets as they have no given weight.

[R1885]

Ehh, fitting all of that in a 4x4 cube will be a bit dicey. I'm going to say it MIGHT be possible, but I wouldn't count on it. Why not go with a simple wedge?

[RedSawn]

Well, really because I don't want to go for a cookie-cutter design x) That, and I -never- make things easy for myself (Though funny enough it usually turns out alright in the end)

EDIT: Took a little visual planning to see I wrote myself into a corner. Arranged the parts and put it to a shell, scale I used is 3 pixels for every millimetre. Sheck is the red line.



From above, it's not so bad, if I haven't made an error. 8.66x3.81x7.66 cm (4 inches is 10.16cm) are the projected bot dimensions without a weapon, if more space or weight is really needed for whatever other parts are needed and I do end up using a OrangeRX, the case can be removed to save about 6g and a sizeable chunk of the main compartment. A few assumptions are made - such as being able to mount the micro motors sideways to save space and keeping the RX and battery sideways for the same reason, and that 1mm armor is enough for fairyweights/UK ants. Biggest problem here is that the side panels are not fixed very securely, that and only having space for a 9mm wide servo. I've found out about High Voltage micro servos that will run directly from 7.4v, but those are 11~12mm. There are still some 6V servos that make the cut, just the voltage to them has to be regulated by whatever means.



But here there's a clear problem. Using the 1.5 inch diameter wheels, even while side-mounting the motors to save 2mm of the space, and squeezing the most room out of the chassis without extending past the wheels, the servo would have to be at the most 9mm wide, 14mm tall, and still be powerful enough to lift 150g on a 4/5 cm spike. 9x14x24.

I think I'll look at the 1.75 inch wheels again and see what comes of that. 6mm might make a big difference.

UPDATE:



1.75 inch wheels theoretically allow enough space for a 9x23 servo, which gives the option of the Hyperion DS09 SCD http://www.soaringusa.com/Hyperion-DS09-scd.html or something like the Ripmax SD100 http://www.sloughrc.com/default.asp?itemid=P-SD100 Ground clearance is a bit crappy though. making the chassis taller is unnecessary too.

[Conraaa]

Anyway you could use gears or small belts to get one motor per side?

[R1885]

Dude, you're going to have serious turning issues with your wheels that close. Maybe you should use 1 1/2 wheels instead of 1 3/4 wheels.

[RedSawn]

Anyway you could use gears or small belts to get one motor per side?

That's one of the other ideas I had, and it would free up the space needed too, but I haven't built a robot before, let alone made belt drive. It might be out of reach for a first project. Then again, this bot as it stands might just be as well. Eh.

Dude, you're going to have serious turning issues with your wheels that close. Maybe you should use 1 1/2 wheels instead of 1 3/4 wheels.

I would probably use 1 1/2 anyway. I'd go for the lower profile any day when it can be helped.