Scale Tank rebuild, what motors to use?
 

A few weeks ago I was struck down with the 'See it - Want It' virus, and ended up coming home with a 6th scale Challenger 11. Main battle tank for the British Army (think Abrams but with a tea urn).
At 1/6th scale this thing is big and heavy, about 80kgs with batteries. It runs on a pair of 12v motors but it can barley hit 3-4mph.
What I'm looking for is more like 8-10mph or more, but with the weight of this thing I can see the price going up with every mph over that.
If anyone can give me some pointers on a better system, brushed or brushless, I know its not the normal line of questions but i'm sure you guys can help.

cheers steve

First of all, are you going to stick with the stock radio? Because if you decide to upgrade to a better one, the only high end radio I can think of with a "tank mode" is the Nomadio.

Next, what is the gearing like? If they are close to direct-drive right off the motor, an outrunner setup should work well since they spin slower overall and still have lots of torque. You'll probably need two ESCs though...

Brian, I'm going to keep it on sticks,(Spectum DX7) simply because I need 6-7 channels for the turret / main gun / big bang stuff. At the moment the drive is controlled by both sticks Two speedos across two channels. I think this is the best way, as its easier to control turning at low speeds, although I have seen a plug in mixer that will mix left/right/forward /reverse on one stick (like the Tamiya's)
The gearing at the moment is via a big transfer box with quite a few gears in it. I was hoping bin this and use a chain drive system,( to save a bit of weight) if I can get a motor/controller that turns slow/smoothly enough.
How should I work out the gearing for this one? do I measure the tracks or the drive sprocket?

If you keep the stock gear box, you're gonna have to either calculate the various ratios, or simply turn the input and count how many times the input has to be turned to get one output turn. Mutiply this by total motor speed, then multiply by sprocket circumference. Divide that whole number by 1056 to get speed in mph.

If you want to go chain drive, you can work backwards. Take your desired speed in mph, multiply by 1056, divide by sprocket circumference, then divide by whatever radio created by the chain drive setup. This number will be your total motor speed needed to drive at the speed you want. Divide that by battery voltage to get the kv you want. Since a single chain drive setup will be pretty low, you're probably gonna want to go with a slower outrunner setup.

BTW: You might want to think about how fast you want to go. Those tank treads may not like to spin fast enough to hit ~20mph. You know what a ballooning tires does when it breaks; imagine that happening to a tank tread! :036:

When you get closer to deciding how you want to gear this, post back here and I'll show you how you can use my R/C calculator to do the math for you.

Good point about the speed of the tracks, especially as they travel twice as fast as the tank.:026:
I have been told they are good for 10mph. Which is about right for a scale top speed on tarmac. Off road is a lot less. In reality it will hardly ever see top speed, its more about tearing up the turf than setting speed records.
I'll come back with some numbers, cheers

Hey Brian, I have some figures. The Transfer box gives 16-1, but I still would like to loose it, as its so heavy.
The circumferce of the Sprocket is 361.1mm As for the Voltage I was kinda hoping that 24v would be enough, what do you think?
I am still wondering about the chain drive raitio, Is it a case of getting the biggest redution in the space available?

Got a picture of this beast? Sounds really cool!

just one :028:

http://img.photobucket.com/albums/v2...y/P1060375.jpg

I'm looking forward to crushing a few Touring Cars with it.:027:

Hi, lots of people get scale speeds wrong by just divideing the speed by the scale factor without taking account for the scale time, scale speed is actualy the square root of the scale factor. For a chalanger 2 that has a top speed of 38MPH its 1/6 scale speed is 15.6 mph not the 6.3MPH that seems logical at first.

Maybe Mike could make you some 7075 tracks that can take it.

As for the power system, at 80kg it would take less than 2KW to maintain the originals power to weight ratio, so a pair of XLs may be enough if you can gear them short enough to make enough torque. If you have the cash a pair of 3080s wouldn't hurt I'm sure.

I believe Mtronics did a brushless tank type esc a while back, it was like two esc's with a main controler. the last time i looked i didn't see it, but one might pop up on Ebay or something

I'm not an expert so I won't recommend a motor but have you tried looking into the robot website? Many battle bots are heavier and faster and use skid steering.

Eccentric, go straight to the top of the class!!!.
No I hadn't thought about it :024: , After some Googling I found the FightingRobots forum ( man they are into some serious engineering) and that led to this....http://www.technobots.co.uk/ and only 10mins drive from my house.
I can take it down for them to have a look at.....cheers

this is a cool project,once you get the drive sorted you can start thinking about weapons ey.:028:

That's a stroke of luck that technobots is just down the road,they should be able to help.another good resource for little gears and sprockets and such in the UK is this place http://www.hpcgears.com/.

Hey Gustav, hows tricks? cheers for the link.
Yup it is a right result indeed....It will take all the guess work out being able talk to people that have done it before........and no shipping to pay, that will be a first:dft012:
I'm abit restricted on what I can fire out the end though....this is England after all. but there are still a couple of choices.....paintball gun maybe, shotgun blanks are another, but again you need a firearms licence......suggestions on a postcard pls

I cant believe you'd never heard of technobots- they were/are big suppliers to the robotwars guys, back in the good old days (its an underground movement these days since the tv show bit the dust). There are a myriad of different controllers available, and compact reduction boxes too. There were plenty of tank/tracked style vehicles on the show, and they were more than capable of 20mph+ & all the abuse they had to endure ment they had tracks that could shift 100kg robots.... serious engineering indeed.

On the weapons side- you dont need an FAC to buy 9mm blanks as far as Im aware. Depends if you just want big bangs, or an actual firing turret- in which case a mini bb gun might be good (small & easily fitted inside the turret).

I used to shoot, before tony blair and Dumblain. You dont need a FAC for a shotgun, its a much less stringent shotgun licence, for firearms you need to have been an active member of a gunclub for 2 years and pass an in depth security check, my police firearms officer told me that for a shotgun licence you just need to have never been commited on mental health grounds and never been convicted of a violent crime. You need no licence at all for a blank firer

Thats interesting about the shotgun license. There is a clay pigeon club where I work (Britannia Royal Naval College), so I could roll up one afternoon with a gert big under&over beauty and not have to borrow one of theirs. Zery interesting indeed....

Yeah don't go getting arrested or anything,maybe stick to BBs.It would be cool if you could get some little mortars to work,that explode on impact like.Remember those little packets of exploding thingys wrapped in paper you could get in the newsagents,you had to throw 'em pretty hard though so it probably wouldn't work.still, mortars would be cool.

Snap-its :dft009: could get 2 boxes with my pocket money......spend all afternoon emptying them into a brown paper bag and then hurling it at some poor unsuspecting cat .......priceless

Well the shotgun blanks maybe worth some more investigation. cheers guys, I have found some plans for a 6 chamber revolving job that would be possible to make.:036:
BB's would be an easy option sure, but a bit lame don't you think, although this thing has a machine gun mounted next to the main barrel its just abit of 1/8th tube sticking out ATM but its a definite possibility.

The Challenger also has the capability to make smoke by spraying diesel into the exhaust ,check out the utube clip
http://www.youtube.com/watch?v=ZXbEDxUPX3A&NR=1
it would be nice to replicate this too. I was thinking about a 12v soldering iron as the element for a smoke genorator or mabye a glow plug from a deisel engine (anyone know how hot do they get?), but it will need an atomizer of sorts too....any idea's??

BB gun for machine gun... definately. An a revolver cannon.... hehehe.
I think a battery operated soldering iron operated via a remotely operated on/off switch would be simple to make. Then a small pump (pc water cooling system type) could be used to squirt diesel or someother liquid that smokes when hot on to the iron- use a needle from a nitro engine= ready made atomiser, and it would be adjustable too (a carb assembly could be easily modified= fuel tank-pump- fuel tube to carb with needle- sprays onto iron- lots of smoke). You might need a small fan to blow the smoke out of the dummy exhaust, since the real thing injects diesel into the exhaust like you said so the exhaust gasses force the smoke out- no such pressure in an electric model, so fan would be needed. I think that would work with a bit of jiggery-pokery to fit it all into the tank.

I knew there was a use for that old Revo Carb!! thanks Neil

I am a genius, yes. But an evil one.....

No problem- I like tanks, and guns, and burning stuff, so I look forward to seeing this project progress.

The tanks are super cool!

I want to see videos of you crushing the TC's!!!!

A little update, I have settled on a pair of 650w wheelchair motors ( after a chat with the robot bashers) and will run it on 24v.
Its all stripped down and i'm building a new steel tub as I have just bought a MIG welder ( o'dear) They do say practice makes perfect, so it may be some time before I update this again.:002:
I have found a suitable method of getting the bang/smoke from the main gun......http://www.hfmgroup.com/professional...s/maroons.html
Stage pyrotechnics :036: can be electrically fired, and my Government thinks them safe enough to let me have them with no paperwork attached......cool

My god. We can buy those with no need for any kind of license, and all those other items too? I just have this vision of one wired up to a door bell on halloween.... that should keep the annoying little trick-or-treaters at bay!
Nice find dude.

Another option for the smoke is to use a Schulze controller and route the smoke through the gun barrel. :)

Nice one Brian, your on top form tonight .......PMSL

I was thinking the same thing, made me ROFL too.

It was the first thing that popped in my head. :)

The funnies things have a ring of truth to them...

Very well said, Neil.

Brian..........LMFAO.

LMAO!

Gee Brian....tell us what you really think of Schulze controllers! :005:

lol, from what I've seen, they make better furnaces than controllers... :)