RC-Monster Forums  
RC Monster

Go Back   RC-Monster Forums > Support Forums > Crawlers/Scale Vehicles

Reply
 
Thread Tools Rate Thread Display Modes
Scale Tank rebuild, what motors to use?
Old
  (#1)
cabking
Guest
 
Posts: n/a
Scale Tank rebuild, what motors to use? - 05.07.2007, 04:06 PM

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
   
Reply With Quote
Old
  (#2)
BrianG
RC-Monster Admin
 
BrianG's Avatar
 
Offline
Posts: 14,609
Join Date: Nov 2005
Location: Des Moines, IA
05.07.2007, 04:21 PM

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...
  Send a message via Yahoo to BrianG Send a message via MSN to BrianG  
Reply With Quote
Old
  (#3)
cabking
Guest
 
Posts: n/a
05.07.2007, 05:44 PM

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?
   
Reply With Quote
Old
  (#4)
BrianG
RC-Monster Admin
 
BrianG's Avatar
 
Offline
Posts: 14,609
Join Date: Nov 2005
Location: Des Moines, IA
05.07.2007, 05:53 PM

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.

Last edited by BrianG; 05.07.2007 at 05:54 PM.
  Send a message via Yahoo to BrianG Send a message via MSN to BrianG  
Reply With Quote
Old
  (#5)
cabking
Guest
 
Posts: n/a
05.07.2007, 06:35 PM

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
   
Reply With Quote
Old
  (#6)
cabking
Guest
 
Posts: n/a
05.08.2007, 06:39 PM

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?
   
Reply With Quote
Old
  (#7)
jhautz
RC-Monster Mod
 
jhautz's Avatar
 
Offline
Posts: 4,216
Join Date: Apr 2006
Location: Chicago, IL
05.09.2007, 01:13 AM

Got a picture of this beast? Sounds really cool!


I can't decide if its more fun
to make it...
or break it...


Silent...But Deadly


   
Reply With Quote
Old
  (#8)
cabking
Guest
 
Posts: n/a
05.09.2007, 07:24 PM

just one :028:



I'm looking forward to crushing a few Touring Cars with it.:027:
   
Reply With Quote
Old
  (#9)
nativepaul
RC-Monster Aluminum
 
nativepaul's Avatar
 
Offline
Posts: 522
Join Date: Jan 2007
Location: Sussex, England.
05.09.2007, 09:46 PM

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.

Last edited by nativepaul; 05.09.2007 at 09:48 PM.
   
Reply With Quote
Old
  (#10)
crazyjr
RC-Monster Dual Brushless
 
crazyjr's Avatar
 
Offline
Posts: 3,786
Join Date: May 2005
Location: georgia
05.10.2007, 01:03 PM

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


Work because i gotta, play because i wanna

People here hate Nitro, I love it. I start it, run it about 50 ft from me and it dies, I go after it. Perfect exercise
   
Reply With Quote
Old
  (#11)
Eccentric
Guest
 
Posts: n/a
05.14.2007, 12:04 PM

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.
   
Reply With Quote
Old
  (#12)
cabking
Guest
 
Posts: n/a
05.14.2007, 07:46 PM

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
   
Reply With Quote
Old
  (#13)
Gustav
RC-Monster Aluminum
 
Gustav's Avatar
 
Offline
Posts: 916
Join Date: Jul 2005
Location: UK
05.15.2007, 07:16 AM

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/.
   
Reply With Quote
Old
  (#14)
cabking
Guest
 
Posts: n/a
05.15.2007, 05:04 PM

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
   
Reply With Quote
Old
  (#15)
suicideneil
They've been naughty boys, havent they Mr. Flibble
 
suicideneil's Avatar
 
Offline
Posts: 7,491
Join Date: Feb 2007
Location: Devon, England
05.15.2007, 05:55 PM

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).
  Send a message via MSN to suicideneil  
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



RC Monster




Powered by vBulletin® Version 3.8.1
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
vBulletin Skin developed by: vBStyles.com