First featherweight!

Hey everyone, I've been reading around on the forums and now I believe I've got the majority of parts decided on. If you could just quickly have a look over before I confirm the ordering of everything.

So its just a simple wedge robot, which will most likely involve a lifting arm using a car jack, or an actuator. 2WD using Gimson motors (the 14.4v version) to power it. The wheels are 78mm from the Gimson site although I may also get the blue robochallenge wheels (100mm) too.

In terms of batteries I was looking at hooking up two 9.6v NiMH packs in series most probably 3.7Ah, 4.3Ah or 4.6Ah (advice please).

I've got a spare 16.8v drill around which I may be using on the car jack. I've already got the transmitter and receiver. Entire armour and chassis will be HDPE, most likely 10mm-12mm.

The main thing I'm unsure about is speed controllers. I've seen many recommendations around the forums such as electronize and botbitz. I myself was looking at the Sabertooth 2x25 (or the 2x12 is it doesn't need to handle so much current).

Thanks in advance for any help! Dan : )

Also, this bot is most likely not going to be competing or anything, its just something I've always wanted to make (since robot wars is awesome!). Perhaps I'd make and compete with a second FW :D

The Gimson GR01 14.4V want a tad more amps. I would advice a Scorpion XXL, or else the Botbitz controllers.

We use a Gimson GR01 9.6V/Scorpion XL combo, and it moves well, is very controlable, but doesn't have an abundance of power.

I know, a tad more expensive; on the other hand, all the XXL's and XL's Team RCC has in use didn't fail us. Except 1 time, and that was a bit of swarf , after removing the speedo worked again.

Concerning batteries. LiPo batteries ain't as expensive anymore, and the more strick rules don't offset the advantages.

A 4S ( 14.8V) 3000 mAh pack costs between £20 and £45 delivered at your door.

Would the Scorpion XXL offer anything much over a Sabertooth 2X25 though?

From what I can see the sabertooth is the same price but 25A and 50A continouous and peak respectively, 5A higher than the XXL for both. Also there'd be shipping involved for the XXL (and I'd probably want to get the mounting case/fan too!)

It seems the XXL has tad higher dependability.

But that could be me.
Team RCC prefers the Robot Power speedo's.
Hannibalito III uses the XXL, Hannibalito 4 the XL.

Kashei and Bullfrog use the Sidewinder .

if your not going to compete then the sabertooth 2x12 would do just for driving it round at h0me

Used all the above speedos, my review of them all;

Electronise.... relays sticking is a common fault, and control is pretty weak.

Sabertooth.... Everyone I've had seem to forget the centre point during a fight... Don't like any dimension engineering products.

Scorpion XL ... Probably give the best control of all 4, good customer support, very reliable, current handling is a bit low for the price. Nice and small... Would need to make your own surround.

Botbitz tz85a.... Great value for money, reliable, good customer support, good current handling, good all rounder... Would be my choice.

Botbitz tz85a.... Great value for money, reliable, good customer support, good current handling, good all rounder... Would be my choice.


Could you post a link Sir, so I can purchase some :)

Google is your friend

http://www.botbitz.com/

see ESCheap85

Doesn't Cobalt use a Scorpion XXL? The way that thing drives it must be pulling more than 20amps?

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Originally Posted by maddox10

A 4S ( 14.8V) 3000 mAh pack costs between £20 and £45 delivered at your door.

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In terms of power I was thinking of 19.2V because it's still within the limits of the Gimson and I'd get a fair amount of extra torque and RPM. As for LiPo, I don't particularly mind paying the extra, but just quickly looking on eBay there are so many different makes, any particular recommendations?

Also the botbitz suggestion seems fine, I'm guessing I'd need one per motor or can they control two? Is there anything else I'd need to go with them (a BEC?, from what I've gathered it's just to not require an external battery pack powering the receiver although I have a few external packs already.)

Thanks, Dan

Edit: This Lipo pack for example. Would that be suitable? Also what's the additional ribbon cable attached to it, is it for charging?

I think Calum particularly recommends flightpower lipos :rofl: :rofl: :rofl:

The other lead is for balance charging- you need a charger than can charge lipos. For cheap lipos I recommend the gens ace range on giant shark, it hasn't failed me yet

There's a thread on here somewhere, where I asked a series of questions about Li-Po.

The cells need to remain in 'balance' and this is achieved by using a charger that monitors the voltage of each cell individually. This is done via the extra cable, one lead for each cell and a ground.

i have botbitz escheap85s.
looking forward to see the way it drives

Quote:

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Originally Posted by Mokichi

In terms of power I was thinking of 19.2V because it's still within the limits of the Gimson and I'd get a fair amount of extra torque and RPM. As for LiPo, I don't particularly mind paying the extra, but just quickly looking on eBay there are so many different makes, any particular recommendations?

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5S is 18.5V nominal in LiPo, but 21V fully charged.

On recommendations. We have fairly good results with the Turnegy Nanotech in Hannibalito 4. But that's a 3S 3300mAh (11.1V) pack powering the Gimson GR01 9.9V combined with a Scorpion XL.

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Also the botbitz suggestion seems fine, I'm guessing I'd need one per motor or can they control two?

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Botbitz controlers are single motor controlers, so you'll need 2 .

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Is there anything else I'd need to go with them (a BEC?, from what I've gathered it's just to not require an external battery pack powering the receiver although I have a few external packs already.)

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A BEC is a battery eliminator circuit.
The main advantage is that you have flat reciever batteries when starting up the machine and realising D'OH , I forgot to turn off the reciever pack.
Moost modern speedo's have a BEC. But I fear it's one of the weak points of the Robot Power products. Those BEC's were designed when 40MHz was the norm, and an old school 40MHz reciever doesn't need as much power as a Dual 2.4GHz Spectrum BR6000. I don't know how the more modern recievers are concerning power, but the older DSM1 type recievers are hungry.

The BEC on the tz85a is 5amp.... wont struggle to power most rx's. Ive used botbitz on dsm1 and dsm2 and it worked fine on both.

Gimsons arrived a few days ago, and botbitz ESC's have been ordered.

In terms of battery I was looking at either Opti power LiPo or a cheaper (local) alternative

Otherwise two 9.6v NiMh packs from similar to this

I would prefer to voltage to be above the 14.4v of the Gimsons so I get a bit of extra speed/power. Also for either option could someone please recommend a good charger/balancer, thanks!

For a base plate I may use thinner HDPE (6mm) as there's less play room that I thought between the Gimson's plastic mounts and the 78mm wheels! I may purchase a couple of 100mm robochallenge wheels for this reason.

Hannibalito 4 uses 170mm wheels on a set of 9.6V Gimsons. Speed is fine as you can see here, even if we only use a 3S LiPo pack.

I can imagine the speed would be fine if my calculations are correct! xD

17cm x pi = 51cm ish
51cm x 530 (RPM) = 27030cm/min
27030cm/min --> mph = just over 10mph

Because of the smaller wheels I'm using, either 78mm or perhaps the 100mm robochallenge ones, I'd need to use more voltage to get a more adequate speed. Again my calculations would suggest that without increasing the voltage.

78mm wheels = 5.2mph
100mm = 6.8mph

Probably the maths is wrong though xD

RPM is a tad higher. 9.6V=530 rpm= 55.3 rpm/v so 11.1V gives us 613 rpm= 19.6km/h (12mph), and that nominal.

Full LiPo's are 4.2V, so add another mph when starting.

Quote:

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Originally Posted by Mokichi

Also for either option could someone please recommend a good charger/balancer, thanks!

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I've got two of these chargers:

http://www.giantshark.co.uk/power-a606- ... 05325.html

Can't really go wrong with them. They do everything from SLA through to various lithium types, come with a bunch of different charging leads, can be powered off the mains (a lot of chargers only have DC inputs, so require either big batteries or a separate AC power supply unit) and, best of all, they cost less than £30.

The downside for lipos etc is that you can only charge up to 6S packs as it doesn't have balance charge inputs for any larger packs. Depends on whether you envisage using larger packs in the future.

For a feather you wouldn't be using anything higher than 6s and if you are you would likely use two 5s packs for a 10s pack

Quote:

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Originally Posted by Mokichi

Because of the smaller wheels I'm using, either 78mm or perhaps the 100mm robochallenge ones, I'd need to use more voltage to get a more adequate speed. Again my calculations would suggest that without increasing the voltage.
78mm wheels = 5.2mph
100mm = 6.8mph

Probably the maths is wrong though xD

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Unfortunatly,upping the voltage has another effect next to increasing the speed.

Basic principle, double the voltage, double RPM and double the amperes drawn.

RPM is per volt, and a constant for every type of permanent magnet brushed motors. The Gimsons 9.6V, after gearing do 55.3rpm/V

We also know that 30A is nice , and will allow motor and speedo to survive stall for a reasonable time- meaning, unless you're a utter fool and keep the power on for seconds even if Sir Killalot is parked on the feather- meaning 300W is our aim for these. Compared to the Speed 900 setups we use, it's absolutely anemic. But it does the job for a reasonable pricetag and ease of use.

Now, 300W ain't the max stall current in these motors. 9.6V*85A=800W+. Imagine what a 800W soldering iron can do.

But double the volts, you also double the amps flowing. Ergo 19.2*170A=3264W. Yes, but not as a motor, but as a fast melting heater. Magic smoke, thank you.

A rule of the tumb. Commercial motors -like Bosch 750, Iskra , wipermotors, window lifters, Maxon gearmotors and such can be overvolted safely for our purposes to 150%.
Batterydrills are a strange duck in the pound here. Some will cope, others will burn. The better the brand, the more will cope.

RC motors, if the brand says max XX volt, be assured it's the max, and even a tad over it.

But remember, an electric motor will only draw as much power as required to do the job. Dave's spinner proves that. During spin-up the amps go trough the roof, to taper off to very acceptable levels once up to speed.

Add this info to the fact that normal , and affordable, brushed motors are only 75-80% efficient, you can imagine that after a fight even non overvolted motors will get warm. Drawing 100W means 20-25W are converted into heat, and we solder a lot with a 20W soldering iron....

Here is a great page on the Biohazard website on motors. Also check out the other pages.

http://www.robotbooks.com/motor-tips.htm

Heat is proportional to current squared. So doubling the motor voltage will quadruple the heat!

Also the iMax B6 is a popular cheap charger. I think I got mine for £8 from Hong Kong! Although I believe it to be a copy as most cheap ones are.