sgtPancake

Heyo

I´m so very, very new in the RC and electronics world, but still I felt like trying it out. I have a huge passion for tanks of all eras.
So I started a scratchbuild of a Hetzer tank destroyer a couple of weeks ago, scale 1/6.

And now I´ve come to the point that I really have to determine the choise of electronics. My thought was to start by getting a motor and then continue with the rest.
I have been looking at motors for 2 weeks and I can´t figure it out what I will need.

I´m thinking of running the thing on 12v, its gonna weigh about 40-50kg (I guess). Power over speed, topspeed maybe around 10-15 km/h.

What motors do you use for your 1/6 scale tanks?

lposter

Good drill motors with low gearing might do

mcm308

I dont know but if I was building a 1/6 tank.. i would be looking at 12V starter motors, snow plow pump motors, etc.. The older Meyer snow plow pumps have nice small 12V motors on them...

Cold Comfort

My Feedback: (1)

Go to rc tank combat you'll find out everything you need to know about 1/6th scale. If you go to tank index my tank is T061 a T34. I would copy and post a link , but I am at work and the site keeps getting blocked by our filters. At least I can get rc universe.

Cold Comfort

My Feedback: (1)

http://www.rctankcombat.com/tanks/T061/ Here's my tank it should give you a idea of what the average setup is like in most 1/6 tanks. The site itself is a fountain of info for all things 1/6 scale.
Greg

DeadTom

Very cool build, did you do it all yourself?
Where did you get the plans for the plywood design?
If you don't mind me asking?

Cold Comfort

My Feedback: (1)

Yes I built it myself. The design was based on T005 http://www.rctankcombat.com/tanks/T005/. Unfortunately at the time there were no other paintball tanks in the area to do battle, but I see that there is three guys in the province starting builds so maybe in the future we can get together and paint each others tanks with some paintballs. It's been several years now since I built it so some reworking will have to be done.
Greg

Panther G

Now see, if I where to build or buy a 1:6 scale tank it would have to be a paintball tank. Why else build it. especially since you can get paint balls in different calibers. 45 cal, 50 cal a 68. Nice variation for different gun sizes on different model tanks.
i would love to do a modern tank with a 120mm gun or a WWII era Pershing .

sgtPancake

Fantastic build! And there s alot of valuable information! Very neat and nice built Greg!

So for an instance; I have 2 12V motors, each of, lets say (out of the blue), 20 Ampere. Then will I need a battery that is capable ot 12V and 40 Ampere to run it?

lposter

I could be wrong but....

if the tank is 60 kg and you are using 12 v motors and lets say you sent it up a slope of 30 degrees at a speed of 4 m/s (15 km/hr from your first post) ... then thats going to take, roughly, over a 1000 W of power needed to get it up the hill at that speed. At 12 V, and W=VI then you will need motors of a big size (because they could draw in excess of 100 A).

Not to mention a bloody big ESC.

And a whole lot of batteries!

Are you sure you want a speed of 15 km/hr? Thats like 4 m/s. It must surely be very fast for an armoured vehicle.....

Im not sure about maximum current draws on 12 V batteries.....but dont mistake Ahours for Amps. ie. if its a 45 Ahr battery then you could draw 90 amps for 30 minutes. The maximum draw on a car battery can be way more than 40 amps.

Its not how many amps such a battery can deliver....its how many minutes you can draw that current for. And driving a heavy vehicle up a hill at 15 km/hr is going to suck the life out of any battery you can get in there in a shorter time that you might think...

I could be wrong though...

p

sgtPancake

Thanks Iposter! That was really helpfull and the quote "The more you know, the more you know that you dont know" is getting to me

However I was thinking to just start somewhere and actually try and see what works and what is not. So I bought 2 cheap screwdrivers, they don´t give me any clue of what speed controllers I would need for them. Since I only know the volt (12v) and neither the watts nor the ampere for the motor. In the documentation for the screwdriver however it sais" Capacity 1.5Ah". I guess this is the battery?

EDIT:
Oh found something else! I have the Torque. That is 8nm and I have the RPM 550.

P = τ x n x 2 x pi (P=watt, T=Torque, N = Rotations Per Second, PI = 3,14)

That gave me 460watts of the motor and that will convert to 38A.

wright 971

Hi Disability scooter motors or wheel chair motors .Check with shops that sell and repair them ,they sometimes scrap off old ones but the motors may be good.

regards pete

lposter

That sounds like the battery......irrespective of the maker, most cheap brands of screwdriver actually use the same or similar motor. If you know what yours looks like, go online and try and find one that looks similar (and costs similar) . You can get luck and find that one shop or dealer lists more information than the other for a screwdriver that looks like yours.

And what you need to find is the torque rating (or maximum moment or whatever they call it). Its often more than you'd think as driving screws actually needs a bit of torque.

Heres a link to ao bog standard 12 v screwdriver. The torque is listed on the right as well as the rpm range.

150 inch pounds max torque is 16 Nm which is probably enough to move 40 kg around I guess.

You can caculate stall current or max current and then just buy an ESC that is a bit above that.

Dont forget you have to remove the torque limiter on these types of drills but its five minutes work and a couple of grub screws.

p

lposter

That sounds like the battery......irrespective of the maker, most cheap brands of screwdriver actually use the same or similar motor. If you know what yours looks like, go online and try and find one that looks similar (and costs similar) . You can get luck and find that one shop or dealer lists more information than the other for a screwdriver that looks like yours.

And what you need to find is the torque rating (or maximum moment or whatever they call it). Its often more than you'd think as driving screws actually needs a bit of torque.

Heres a link to ao bog standard 12 v screwdriver. http://www.harborfreight.com/12-volt...ver-69360.html

The torque is listed on the right as well as the rpm range.

150 inch pounds max torque is 16 Nm which is probably enough to move 40 kg around I guess.

You can caculate stall current or max current and then just buy an ESC that is a bit above that.

Dont forget you have to remove the torque limiter on these types of drills but its five minutes work and a couple of grub screws.

p

sorry I forgot the link and I coundt edit

lposter

I see you have an edit on your post....8 Nm might be a bit skimpy for a big heavy 60 kg tank. It may move but not uphill! Saying that its not so bad if you could reduce the weight of the tank.

Remember,,,,,,if you have two motors then the draw on teh battery will be twice what you calculate for one motor.

Screwdriver motors are the recommended motors for battlebots up to about 120 lbs so you might be OK or just on the verge of OK.

Its a pity you cannot shed a few kg off the tank. 60 kg is a monster!

If those drills wont move it uphill then you'll need either more expensive drills or wheel chair motors. But a wheel chair motor will pull your arms off, its hard to get two "matched" ones, are heavy, can be tricky to mount and if the tank gets away from you you may not be able to halt it and it could damage something.

So you will have to install a dead mans switch or something.

Id tailor the tank to the motors rather than build the tank first and then try and get motors. If you see my point..

p

sgtPancake

Yes I found the torque of my screwdriver motor, I posted an Edit my previous post:

"Oh found something else! I have the Torque. That is 8nm and I have the RPM 550.

P = τ x n x 2 x pi (P=watt, T=Torque, N = Rotations Per Second, PI = 3,14)

That gave me 460watts of the motor and that will convert to 38A."

But this calculation shows the current when using all torque there is right? Aka Max current.
So battery-wise I would need a 12v battery that is atleast 72 Ah?

sgtPancake

Ok now we´re writing at the same time it seems

The tank will most certainly not reach 60kg, I´ve started to build the hull now and found some good light-weight material. So I guess the tank will land somewhere between 30-40kg at tops. The batteries are the big weight here. I think I´ll manage with 1 carbattery and that´s about 15kg only that

And yeh Im buildng the lower hull and will now continue with the whole setup of motors/ESC/batteries and so on before I move on, it only taken me 2 hours of work so far so it´s no big deal to rebuild if I have to at this stage.

sgtPancake

Just a quick check before I lay the order; you guys think this ESC would work?

http://www.hobbyking.com/hobbyking/s...w_Reverse.html

lposter

I think thats a single esc. For tanks you usually use a dual controller or two singles?

sgtPancake

Yeh I´m gonna buy two of these, one for each motor right? And connect them to the same Reciever and Battery.

lposter

In all honesty. . . . I would wait until the hull is finished before buying an esc.

Im no expert but you need to decide if you want things like BEC (battery charging when braking)

and so on. Some of the larger robot sites have really good wizards for choosing ESCs.

Im building a tank of similar weigjt to yours, probably less, and i was going to wait with the esc.
But i think I,ll buy a dual from a robot shop so Im fairly sure it,ll do what i need it to do.
P

sgtPancake

I have the hull finished, I´ve also worked out the specs of the motor (had a long 3 hour siting with a, to me, math-genius who helped me calculate it out. Aswell as measuring the rpm and ampere)

But about the ESC. The motor stalls at 85A. Let´s say I have an ESC that is capable of 40A continious current. The motor will apply 40A at 8.26nm. 8.26nm will in my case be able to lift 18kg straight up with a speed of 9km/h. I will never reach 40A by 3 reasons: 1. I will not run it straight up, 2. I have two motors (thus 36kg straight up) 3. the tank will not weigh 36kg.

But still, let´s say I do drive my...50kg tank straight up, which will produce more than 40A. Will that then burn the ESC?
In my mind that will be the case if the ESC hasn´t got a top current (like some does, for example 100A for 2 sec). Or have I missunderstood everything? :S

DeadTom

Is your ESC rated at 40A? If so then you can have a short spike of more aperage draw in a very short span of time. But any large load like the example of the 50kg tank moving quickly up an incline will probably result in a flaming ESC or at least a very very hot ESC. Large heat-sinks and fans would help to cool overly hot ESCs.
Good discussions so far, all good stuff and thanks for sharing.

lposter

You could try and find a 30 A fuse and put one between each motor and the esc?

At least you only fry the fuse then. High amp escs are anything
but cheap!

P

MAUS45

You should be able to run your tank using two of these 45A ESC's. You could run them throurgh a v-tail mixer or mix them via your radio.