Newbie - designing a new heavy weight

12th August 2009, 12:16

Hi everyone,

Im new to this forum, just wanted to introduce myself and say Hi.

Also, I am designing Heavy Weight combat robot and had a question with regards to its locamotion:

Currently i am probably going to use 2 x S28-400 magmotors, with 26Nm torque per magmotor at stall. With two motors my cobined torque will be 52Nm (in theory), once geared down, i have 628Nm total torque (at stall with a 12:1 ratio). If i have four of these motors, i will have 1256Nm at stall.

I guess im being a bit greedy, but i want very high torque and a relatively fast travel speed to maximise ramming impacts. If i use four motors (when i have the cash to by two more that is ) then i could easilly put out the 628Nm of torque without stalling the motor but run the robot at a higher speed as well (when compared to the 2 motor set up). Note: my motors are not attached to the wheel axle, but will all be geared down via chain and sprocket.

I guess this will demand more juice from the batteries and also require larger ones, thus increasing weight. But if its a sensible soultion then I might give it a shot. Though i will need an ESC capable of handling such high currents (most i've looked at can only deal with 120 to 140A for a short ammount of time.)

I want to use the four motors in a differential steering set up, but dont know quite how to wire this up to a speed controller which would normally do 2 motors, maybe i would need two speed controllers, but i cant find alot of info about it. I guess i could wire the motor in parrallel?

Are four motors common amoungst heavy weight bots?

Hope that all makes sense

Any advice would be most appreciated.

P.s, I have seen the superheavyweight category in the FRA regs, is this a standard weight, as it mentions giving prior notification to the FRA before comencing build on a SHW?

Cheers

Mech King

**blazerbotics** · 12th August 2009, 20:06

Hi, nice to see your interest. If running 4 motors off one contoller than you would wire them in parrellel, but the only controller i would look to run 2 mags on is the single channel roboteq, which means you would need one controller per side, anything else would be pushing it. Most robots use just 2 motors, and if they need more power then either up the voltage or get bigger motors, 4 motors does give you a redundency factor but also means twice as much to go wrong! Big Nipper runs 2 mags and has plenty of speed and power. Battery wise i would run at least 3 nicads packs, 4 if you went for a higher voltage. If weights not a problem than 16ah Hawkers would do.

What sort of design are you going for, is it a pusher and will it have a weapon?

There aren't any super heavys in the country (a few in the USA) they would just be too powerful to run in the current arenas.

Alan

**gravity** · 12th August 2009, 21:43

so basically... you have designed a box with wheels ?

You might want to think about a weapon...

12th August 2009, 21:55

Hi Alan,

Thanks for the insight on that. I have been pondering over the Roboteq (AX2850HE) and the Vantec RFDR47E ESCs. Which would you recomend?

Yes, i think i will try and stay with one ESC and two mag motors then. I've been looking at more powerful motors, but they are closer to Â£600 each :shock: .

I am going for a 'technical' pusher, with a hydraulic actuated grapple/flipper, however this may change. I am just finalising the sums and am going to build a simple base to test my motors,wheels,ESC etc on to ensure its functions ok and runs as i have calcualted.

Cheers for the info Alan,

Amir

12th August 2009, 21:57

Originally Posted by gravity

so basically... you have designed a box with wheels ?

You might want to think about a weapon...

Hi gravity, no just chose not to give too much away :wink:

**blazerbotics** · 12th August 2009, 22:20

If just 2 mags then a Wotty 360 would probably be ok, the Vantec has no current limiting which might be an issue if you push the motors hard, also you cant get them repaired if they blow, a Roboteq is about Â£170 to be fixed. You looking at a Storm 1/Draven weapon (http://www.teamstorm.com/storm/index.htm)?

13th August 2009, 08:45

ye similar principle, some interesting pit falls there to learn from, armour wise.

There is scope for change at the moment - im just enjoying being able to design what ever i want without having to ask the permission of my MD, what a great hobby.

Is the roboteq genrally a good controller? Would you recomend that to control 2 mags? I quite like the heat sinking on it and general design......... im a bit of a sucker when it comes to aesthetics. Can these ESC be purchased in the UK or are they all USA based?

**geeza** · 13th August 2009, 22:17

Like Alan says no you won't get a vantec repaired. And the state of play as I understand it is that Vantec have halted production of the big end speedos. A wotty is a great controller and you can get repairs in the UK, a roboteq will require sending to the US. However the roboteq does have a track record with mags, did Big Nipper try a wotty in it at some point?

14th August 2009, 14:18

Hi chaps,

cheers for the info.

I contacted Ian Watt and have the specs for the Wotty360EV. Looks like a winner, and can handle 160Amps for 5 mins.

One thing i forgot to ask was what it looks like,how its packaged and if its heat sinked

**geeza** · 14th August 2009, 16:44

The fets are straight onto an ally heatsink 180x25x20 mm ish. Then this is bolted onto the cast ally case. approx dims are 170x110x60mm - you can have any colour as long as its red!

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