Battery help.

[Ellis]

You will bottleneck those motors with any NiMH pack I know of that you can get in weight. We bought two 18v custom packs for Tormenta 2, (4 drill motors) and put them in parallel, to get an estimated 60a-70a peak amp draw available from them. That figure would drive your motors and not starve them too badly, but the batteries will suffer a fair bit. And they were heavy.

I'd go LiPo. They're a bit intimidating at first, but smart enough chargers will stop before doing any damage if the setup is wrong, and once you suss it they're like any other battery technology. Difference is they weigh nothing and have incredible power figures.

Also, in truth, you'd pay a lot more for NiMH packs anything like close enough to the figures you'd need, than you would for a suitable LiPo pack.

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Two of those motors should get a machine moving around nicely.

[plargen]

I agree lipos are a bit and intimidating at fist but once you've use them and got use to them you won't want to go back to NiMH

[Chris230291]

Li-Ion has a serious disadvantage that makes it rather unsuitable for our application, high internal resistance. In other words, peak power is low. Try to power a robot with Zinc-Air batteries or even Alkaline primary cells...

Cheap, yes, Chinese, yes, crap, no. There are even cheaper Chinese copies, and even those have a reasonable use.

Of course, nobody will stop you buying a Schulze charger for 10S packs or so. But I believe your wallet will object. Mine does.

Ok cheers for the advice fella.
I know Li-Ion's are used to power things like electric bikes, so surely they are suitable in this application? I would have thought they used similar motors to the ones i have which appear to be scooter motors?

We are building COMBAT ROBOTS, not Barbiemobiles.

Primary cell batteries ain't in the rules either, just because they are unsuited for our purposes. But I don't believe, if you turn up with a suitable Li-Ion pack, you would be "disallowed" to compete.

If you want discharge rates, you could look at the Hawker Cyclon SLA cells. Those start @2V 2.5Ah , and those little ones have a discharge rate of 500A+ that's 200C

Haha yes.
Cheers again mate. I'll take a look

I agree lipos are a bit and intimidating at fist but once you've use them and got use to them you won't want to go back to NiMH

It's the maths that confuses me more than anything else. I'd rather the motors melt than the batteries reach their current draw limit. I'm not sure how i'm supposed to work it out :S

Thanks for all of the replies!

[Chris230291]

You will bottleneck those motors with any NiMH pack I know of that you can get in weight. We bought two 18v custom packs for Tormenta 2, (4 drill motors) and put them in parallel, to get an estimated 60a-70a peak amp draw available from them. That figure would drive your motors and not starve them too badly, but the batteries will suffer a fair bit. And they were heavy.

I'd go LiPo. They're a bit intimidating at first, but smart enough chargers will stop before doing any damage if the setup is wrong, and once you suss it they're like any other battery technology. Difference is they weigh nothing and have incredible power figures.

Also, in truth, you'd pay a lot more for NiMH packs anything like close enough to the figures you'd need, than you would for a suitable LiPo pack.

--

Two of those motors should get a machine moving around nicely.

Ok cheers mate. What numbers do i need to look for when searching for Li-Po's? Also, 60-70A? Each of my motors draw that under stall so are they really the way to go?

Chris.

[Chris230291]

Them Hawker Cyclon cells are just really expensive lead acid batteries? I guess the advantage is i can dot them wherever i have free space as opposed to having all of the battery in one lump?

I already have Lead Acids in my workshop. They're pretty much perfect for power delivery but i think the weight is the killer with those.

It's starting to look like i have to make a decision between power delivery and weight?

[Max]

In combat robots the motors are slammed from forward to reverse then stalled against a wall. They repetitive ly have to accelerate drawing huge currents. On an electric bike it sees nothing like this it has to occasionally accelerate then go along at a constant speed, and it only has one of those motors, your talking about having 4! So although lithium ion are suitable for electric bikes not so much for our applications.
If each of your motors draws 60A at stall then you need a battery that can comfortably output 240A (4x60) at burst. I would go for a 5aH battery to supply those 4 motors, this can output 5A for one hour, or 10A for half an hour, or 20A for a quarter of an hour etc. so for the 3minute fight it can supply an average of 100A which should be adequate.
To find the max discharge rate of a battery you multiply the capacity (in Ah) by the discharge rate (in C). So you need a C rating of at least 48C (240/5).
To achieve this I think you need either a Hawker Oddysee SLA battery (very heavy) or an optipower Ultra 50C Lipo like this:
http://www.optipower.co.uk/Catalogue...cat=131&cnode=
This would be very light. You could if you wanted more voltage use a pair of the 4 cell optipower batteries in series.
If you only want to use 2 motors then you only need half the discharge rate in which case I think web some of the cheap hobbyking lipos could supply the current (as long as you choose very high discharge ones- they are always overrated) but I would still choose a 5Ah battery to keep the high discharge rate.
I would listen to someone else though about what capacity(Ah) you need for those motors as I have never used them.

[Max]

Ok cheers mate. What numbers do i need to look for when searching for Li-Po's? Also, 60-70A? Each of my motors draw that under stall so are they really the way to go?

Chris.

He was saying that the 60-70A was what his Nimhs could deliver- that is not enough for your motors so you shouldn't really use NiMhs but instead lipo or Hawker Oddysee batteries.

[Max]

Them Hawker Cyclon cells are just really expensive lead acid batteries? I guess the advantage is i can dot them wherever i have free space as opposed to having all of the battery in one lump?

I already have Lead Acids in my workshop. They're pretty much perfect for power delivery but i think the weight is the killer with those.

It's starting to look like i have to make a decision between power delivery and weight?

I doubt you would use the single cyclon cells but woudonuse buy a 12v hawker Oddysee battery pack then wire 2 or 3 in parralel to get desired voltage. Hawker Oddysee SLAs are expensive but will be able to deliver the amps needed. Those SLAs you have in your workshop would probably not be suitab as they cannot deliver anything like the same amps (they may manage 50A rather than 500A) so would nt be suitable for your robot, they were used on early low power robots but are useless and weigh a ton for no gain.
For those motors your choie is only between good quality lipos or hawker Oddysee SLAs, I imagine they cost about the same so I would definatly go for the light weight lipos.

[Chris230291]

In combat robots the motors are slammed from forward to reverse then stalled against a wall. They repetitive ly have to accelerate drawing huge currents. On an electric bike it sees nothing like this it has to occasionally accelerate then go along at a constant speed, and it only has one of those motors, your talking about having 4! So although lithium ion are suitable for electric bikes not so much for our applications.
If each of your motors draws 60A at stall then you need a battery that can comfortably output 240A (4x60) at burst. I would go for a 5aH battery to supply those 4 motors, this can output 5A for one hour, or 10A for half an hour, or 20A for a quarter of an hour etc. so for the 3minute fight it can supply an average of 100A which should be adequate.
To find the max discharge rate of a battery you multiply the capacity (in Ah) by the discharge rate (in C). So you need a C rating of at least 48C (240/5).
To achieve this I think you need either a Hawker Oddysee SLA battery (very heavy) or an optipower Ultra 50C Lipo like this:
http://www.optipower.co.uk/Catalogue...cat=131&cnode=
This would be very light. You could if you wanted more voltage use a pair of the 4 cell optipower batteries in series.
If you only want to use 2 motors then you only need half the discharge rate in which case I think web some of the cheap hobbyking lipos could supply the current (as long as you choose very high discharge ones- they are always overrated) but I would still choose a 5Ah battery to keep the high discharge rate.
I would listen to someone else though about what capacity(Ah) you need for those motors as I have never used them.

Cheers Max. Thats a very helpful post right there!

The peak stall of the motors is like 90 odd Amps, but right away it drops to 60 - 70A. Like right away.

I just popped out to the workshop and i found i already have 3 of the square 5AH 12V sealed lead acid's and 1 rectangular 7AH one. It's nice to know i'm sorted so long as the weight allows them

Is the "C" rating just for Li-Po's? I noticed that when i was browsing.
I just cant justify that kind of money for a battery at this stage though I think perhaps thats something to look into if i do well in the events, or if enjoy them for that matter! (though i'm sure i will)

Thanks again. Very helpful

Chris.

[Chris230291]

He was saying that the 60-70A was what his Nimhs could deliver- that is not enough for your motors so you shouldn't really use NiMhs but instead lipo or Hawker Oddysee batteries.

Ok. I'll forget about Ni-Mh.

I doubt you would use the single cyclon cells but woudonuse buy a 12v hawker Oddysee battery pack then wire 2 or 3 in parralel to get desired voltage. Hawker Oddysee SLAs are expensive but will be able to deliver the amps needed. Those SLAs you have in your workshop would probably not be suitab as they cannot deliver anything like the same amps (they may manage 50A rather than 500A) so would nt be suitable for your robot, they were used on early low power robots but are useless and weigh a ton for no gain.
For those motors your choie is only between good quality lipos or hawker Oddysee SLAs, I imagine they cost about the same so I would definatly go for the light weight lipos.

O? So a 5AH battery doesn't mean it can cope? :S

Confuzzled! :S