Reliable High Discharge Lipos

I am looking for a fairly low capacity lipo, say 2500-3500mAh, that can do discharge rates of about 240A. (So for a 2500mAh battery it would need to do 100C, or a 3500mAh would need 70C). As you know there are loads of lipo brands out there but which are reliable, safe and long lasting.

The ones I have seen have been...
VoltON
Desire Power
Turnigy
Venom
Thunderpower
Poweredge

What experience or rumours have people heard about these different lipo brands. I am currently using Gens Ace lipos but they dont seem to do a Lipo with a low capacity that does a high enough discharge rate.

Note: I know its a little mad but I don't want to give away the details if this new design turns out to be viable! :wink:

I'm sure you have your reasons, but why not just up the capacity? Would be the easiest solution.

I use FlightPower Li-Pos, seem pretty popular.

Its partially to do with size; bigger capacity, bigger battery, and you end up with left over power. I ran 4 fights at GSL on my 4000mAh drive battery without recharging. I recharged after the 1st fight but the charger could only put 600mAh back into the battery. (well I was only in the area for 1.5 mins not 3)

Theoretically the bigger capacity you have, then the larger continuous current you can deliver for a lower C rating.

Helpfully the Flightpower website has Continous and Burst ratings for all it's batteries do you don't have to do the maths.

An alternative would be to have 2 batteries running in parallel, gives you more options for space. But what on earth do you want with 240a!?

240amp 3.5amp that won't last a fight will it?
I also found this http://www.giantshark.co.uk/gens-5000ma ... 06494.html
which is expensive

what do you need 250 amps for and at what voltage?

try OPTIpower lipos their some of the best lipos on the market

I need a 4 cell, 14.8V, though the motors nominal is 12V...

The motors pull just under 20A at their most efficient, but with the loading they will be under I doubt I will get anywhere near that...

I have found a 4 Cell 4000mAh 50C on the Gens Ace site but its germany only for some reason...

This is still just an idea, it may not even work but hey, we like to set ourselves a challenge!

Once again I'll ask, why do you need 250amps?

How long do you need to pull the 240amps for? Could you have a bank of capacitors in there to give the surge current?

I don't know how long really. The maximum draw of each motor is 120A so the idea is to make all that power available when pushing and driving rather than being prevented by the limits of the battery and ESC's.

I the basic idea is to make the most powerful and robust full body hammer possible. But I have given over 3Kg to a small disc system so when brute force isn't enough we can turn around and use that.

Think a featherweight Tornado and then imagine what happens when you devote over a third of the robots weight to the motors and gearbox's in a featherweight. I think Tornados weight distribution was similar to that in its first iteration without the disc.

Bloody hell, what motors are you using?!?!?!

Why not make just that: a FW Tornado? Same weapon configuration and everything? Do it do it do it do it! :lol:

Also, as I am sure you are aware, power is useless unless it can be put down. I am assuming you'll deal with that with magnets?

You shouldn't be reaching anywhere near 1776W (120 x 14.8V) with even the most powerful featherweight drives - you're fundamentally limited by how much traction you can get on the floor as to how much you'll be able to use before you spin the wheels (unless you're using magnets?) - might be useful to have a play around with this http://www.architeuthis-dux.org/torquecalc.asp


edit: looks like someone was a minute ahead of me!

Assuming I have set up the calculator right says that when I get to 30A of a possible 133A the wheels will spin. and I need 86 oz-in to spin the wheels or 6250g/cm... can someone explain what that actually means beside i have WAY to much power

There's some variables which you're unlikely to know with too much accuracy: the coefficient of friction of the tyres (which will be different on different surfaces) which obviously effects the point of wheel-spin, and also the inefficiencies in the drive-train (friction, heat etc.) which will add to power consumed when reaching wheel-spin. As far as your battery is concerned you only need to rate peak current at a little over the wheel-spin condition, the 'possible 133A' you mention is surely the stall condition (?) which you shouldn't be aiming to reach, the closer you get to it the more power you'll be expending as heat rather than movement.

is there any real point in such powerful motors if I cant get the power down or can you put slick tyres on and the like to give more traction

You could use tracks, depending on how you do it that could increase the friction giving you lots of power. But on my tracked bot the tracks slip on the ground rather than the motors stalling so still not enough friction on my design but that's partly due to the fact the bike tire I used wasn't very grippy and the lack of a wheel in the middle and suitable tensioning means in the middle of the track not much weight holds it on the floor.

The obvious thing you can do to boost traction is to increase the contact surface area by both changing the tyre material and wheel count. Think how Storm II is a 6WD machine with custom tyres specifically designed for the arena environment- specifically for this reason.
Although using a softer rubber compound generally helps, it's worth bearing in mind it can become 'gummed up' with dust and debris from the arena or just wear down too rapidly to be of any use. The orange banebots compound seem like a good compromise between wear resistance and traction from my experience, they're a little softer than the Robochallenge 'Blue' wheels but are not as wear prone as the (incredibly soft) green versions.
Other than that if you're aiming specifically for the Robochallenge arena magnets ought to be worth considering, though they bring their own complexities.

I was going to use 8 of the green banebots wheels, but I know 30S is very soft, I had considered tracks but I know of now way to make featherweight tracks. it seems now that its not a question of power but a question of traction so now I just have to figure out how to maximise traction!

MORE WHEELS!!!

A lipo with a 100A discharge will be more than enough for a rammer

What speedo are you planning on using, seeing as most heavyweight controllers are current limited to about 120amps per side?

Victor 885's, but given I will only be able to use 30A before the wheels spin I am going to need to rework the design to make using that much power worth while. I am certain we can do it and use all that the motors have to offer its just figuring out how. I can see myself doing some tests when I get back to uni on what grips best to Hardox 800.

It seems now that power is not the issue but just fundimental grip. Thanks for your input guys, it never crossed my mind that I would not be able to put the power down. I am going to have to design the Bughatti Veyron of robots to make use of all that grunt!

Take cues from Dave's 540 and go for magnets with 6WD- that's probably the best set-up for mechanical grip that's realistic for a feather.
Also if you're going for the 'Bughatti Veyron' of drivetrains then look into sensored brushless motors & speedos for drive- can't get much better than them these days & they're now pretty affordable, worth a browse on Hobbyking.

I have read nothing but bad reviews about hobby king and rubbish customer service... yet some people seem to have no issues which is strange, its one extreme or the other...

With the Cellite and Ti to make the chassis it is probably possible to make a seriously grippy and torquey robot cos you can devote much more weight to the drive train! I will just have to be careful I don't go up in a cloud of smoke like 540 every other fight, never understood why that happened.

I have to admit I don't have any complaints about hobbyking.
Especialy not if you take care of ordering from the German warehouse.
Also, ordering out of stock stuff won't help a lot.

And of course, you get what you pay for.
If you buy a £10 100 gram brushless with a 3.2mm shaft and a max power of 3S 100A to power your spinner you can expect broken axles.

For everyone that just did what I did:

http://www.teamnovak.com/tech_info/brus ... rless.html

540 on paper and is an awesome machine with a serious amount of power. But that was it's undoing. With that much power there's always a weak link, and when you're fighting that will always be exploited.

Read this the other day and it confirmed what I've always said.

Fights are won in the arena, but the Battle is won in the pits

Your machine can be awesomely destructive, but if you can't last the weekend then you aren't winning the championship. Just look at how well BitzaMk1 did, and that had the side of a dish washer for a front!

LOL the first thing you get in google when you type in sensored brushless :)

Was it 540's motors that kept burning out? It was superbly engineered, I don't know if we can get close to that in terms of mechanical accuracy, all our wheels will probably be out of alignment. (But hey, so were Conkers and that didn't really matter)

Like I said before its just another idea, but it would be a fun robot to drive and Tornado was always a crowd favorite, so hopefully it will be fun to watch to!

540 burnt his motor's out as the magnet was just too much, and geared too fast for the size of the motor. It's fine going off that chart that tells you 30A is fine, but thats not realistic for for more than just driving around.
As soon as you slamming forwards and back, that burst current will shoot right up. Also when you underneath someone with their extra weight giving more grip will shoot that current rating up. 540 needed LOADS of power to stop and change direction due to all the grip, and the motor's just couldn't take it.

If your running without magnets there's not much to worry about on this front - get a decent lipo such as OptiPower of the new thunder power 65C packs (pretty pricey these though) and work from there. With all that power your more likely that the motor's can't hack it rather than the rest of the system if they're particularly small in size.

So am I right in saying that to avoid the same issues that 540 had I would need to fit larger motors and then gear them down further OR use 1 motor per wheel as I do atm with conker. Both of these would ensure that I had more power to deal with the increased grip.

What motors did 540 use then I know that I need to go up from there or change the ratio, that thing was seriously fast so reigning in the speed would probably help

540 used some dewalt motor's, not the big ones though. Very powerful but as you could see just stupidly fast. Being geared that fast reduced a huge amount of torque so by the time the magnets are on its stalling the motor's quite a lot. To get round those issues you would ideally want motor's more powerful than you need, and gear them to a sensible speed, somewhere in between the fast and low speed of what 540 had would be pretty reasonable. I usually aim for around 800-1000rpm at the wheel maximum on 75mm diameter wheels, but that's just my opinion. Any quicker and you are just stressing the motor's more than needed. If you do it this way you'll have less problems if you decide to put magnets in for extra traction.

The way you drive will massively help as well - to help get around these problems in our smaller kits as theyre running for hours is to have custom software in our speed controller's with acceleration ramping built in so that the current when changing direction is massively reduced.

Acceleration ramping and non linear control will be a big help in reducing the spikes.

540 upgraded to Speed 900s to help with reliability at this years champs, but they went too. I know Dave also had trouble with stripping gears, snapping drive belts, burning out motors... There's always a weaker link and getting drive that powerful has it's costs.

Not always. I'm not sure whats causing the problems with the gears keep breaking, maybe too much flex in the gearbox or something. If you make fully enclosed gearboxes with the right ratio's you shouldn't have any problems at all. Dave's gearing still is too fast even with the speed 900's in. He would probably get away without burning up motors if the magnets weren't in.

Ploughbot for example uses astroflight motor's. Much smaller and lighter with plenty of power, but being smaller they're easier to burn out. I use them on 15:1, and will probably make the next set at 18:1 as they're still plenty fast enough. I have fully enclosed 2 stage gearbox with TINY gears in. I'm using MOD 0.5 on the first gear stage and MOD 0.7 on the second. I've never had one strip or break or anything and not burnt a motor out on this set up.

What would people reckon to this set up...

6x (3 per side) RS775 12V Motor + Banebots P60 16:1 Gearbox + 2x 98mm Banebots wheels

I have calculated a speed at the output shaft when running on a 14.8V lipo to be ~560RPM and have a top theoretical speed of 10Km/H.

And at peak efficiency I should get... 16.4Kg/cm at the ground, which seems a little low... hmmm maybe I have duffed that last bit of maths...

That's not a huge amount - I've just ran through your calcs and they look about right.
Those motor's are less than 300w each, fairly high speed so not that powerful really. You'd be better off even saving weight just using speed 900's with a custom gearbox.

Just as a comparison, on Ploughbot running 24v with good lipo's on the AstroFlight 940 motor I am getting 1000rpm ish at the wheels with some losses, 75mm wheels gives me 14km/h or 9mph. Thats a pretty decent speed.
Torque on the floor at stalling is quite different to your 16kg for 6 motors, more like 116kg at stall with 1 motor per side. The astro's are 750W continous, on 24v thats about 35A draw with the effeciency losses. At stall they're 100A max, which takes the power to around 2000w each, probably more like 1500w with losses.
That torque is enough to just about push my old saxo along ;)

would a Speed 900 at 22.2V (6 cell) on a 10:1 ratio work (1 per side, though I did think of using 2 :) ). David runs 6:1 on satanix with his 120mm wheels but he is only using 2 wheels not 6. The bane bots 124mm would be the wheel of choice as we can easy change the shore value of the tyre

Satanix has masses of power. Once underneath I didn't see it struggle once. Thing is, there isn't much point in having drive that is incredibly powerful, because a drill powered robot (such as ours) doing 10mph will hit just as hard as a 1000w drive monster bot doing 10mph. Only benefit I can see to lots of power is if you can get up to speed in a small distance, i.e., lots and lots of torque. Even if you can accelerate to 20mph in the size of the Robochallenge arena, it'll be stupidly hard to drive. 2 drills and a low enough scoop and you're there, in truth.

I'd focus more on making a machine tough and reliable. Rarely is it power alone that wins robot events. In NST's case, it was flawlessly reliable, and it had a powerful weapon. Winning combination.

My point is, a solid Gimson powered box will be just as competitive (if not more so) as a Formula 1 featherweight.

I am not really after speed, my driving is terrible so if I was given a missile like satanix I would struggle. I am kind of after just pure grip and push, like 540 had and then putting plots of armour on to prevent NST from ripping it to bits again. But I am adamant that it will have some kind of active weapon be it a disc or a lifter. (this has veared severely away from the title of the thread!)

Quote:

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Originally Posted by Ellis

In NST's case, it was flawlessly reliable

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Except for that one fault where the weapon motor gets stuck on, yeh it's flawless!