Starting Point

[zoll]

Re: Starting Point

So the two batteries will power all 4 motors for a reasonable time then?

[psycho_fling]

Re: Starting Point

yeh easy

[typhoon_driver]

Re: Starting Point

I advise doing the mathmatics for the problem rather than assuming they will be fine.

The basic way to think about it, batteries capacity is given in Amps per hour (Ah). In other words if a battery is sold as 2Ah then it will provide 2 amps of current for a solid hour (at least in theory it will). Now we can use this to work out if the battery will last in battle. A battle is around 3 minutes long. That is 1/20th of an hour so the 2Ah battery will be able to supply 40amps for that battle (again in theory, it does depend on the batteries internal chemistry if it can make this figure). Good batteries should always be able to tell you their constant discharge rate and their short term discharge rate. The second being used when a large amount of current is required at a motors start up. With regards to a drill motor, I'd say a good average for the time in battle will be of the order of around 10 to 15amps average over the entire battle. Lets say because you are using 4 drill motors each motor needs 10Amps average to push featherweights around for a full 3 minutes. So your drive will require 40amps continuously over the entire battle. You can then use this figure to see if your battery will last the full time.

There are always assumptions in this calculation (there always are in any engineering question) but the key is to reduce their impact on the real world solution. I therefore always like to over engineer robots, throw in more capacity than is required and beef things up. Of course this comes with weight problems but its all part of the bigger problem of coming up with a reliable machine.

[zoll]

Re: Starting Point

Cool so by that logic 3.7 provided by those batteries should be enough (i assumer 3700mAh =3.7Ah)

[psycho_fling]

Re: Starting Point

it does i let you work out Gary's math

you will see with robnoteers a slight split one side being the math side really getting things perfect so they 'shouldn't' go dodgy others will guess and hope for the best. saying this i myself differ with approaches depending on what robot i'm building

have fun,
alex

[zoll]

Re: Starting Point

whats the difference between the batteries you linked for me and say http://cgi.ebay.co.uk/7-2V-3800mAh-N...item35a4af5dc8 is it just the make, ie cheaper brand worse quality even thought they claim to do the same thing?

[typhoon_driver]

Re: Starting Point

Yes those are worse quality. When buying parts for robots you pay for quality. You can get away with going cheaper but you must know which batteries or components specifically you are looking for.

I can almost guarantee that those batteries will run flat very quickly and won't be able to provide you with the current you are after.

[zoll]

Re: Starting Point

Just ordered some HDPE, what would you recomend for fixing it together, angle iron and pop rivits or box section and bolts?

[muchalucha]

Re: Starting Point

pop rivets arent a great idea for hdpe , and you would still need somehting to rivet it to. So i would suggest angle iron on all the right angles , with bolts and using wood screws and blocks of hdpe for unusual angles joints or joining 2 flat pieces togethor. Have you decided ona weapon ?

[zoll]

Re: Starting Point

Well i wanted an axe or lifter but dont really have the knowledge to make one, so might just not have a weapon and build one in at a later date.

It was suggested that I could weld HDPE has anyone done that and does anyone know where I can get the attachment for a heat gun to do this in the uk.

If not i will got the bolt and angle iron route, will i need any special tools to cut and drill this?

[muchalucha]

Re: Starting Point

to weld hdpe you will really need a crash course from someone who has done it before. As for a weapon, a humble scoop would be good a s a first weapon , this bot should have quite a bit of power to so a scoop would make a very competitive bot.

[zoll]

Re: Starting Point

anyone have ian watts email please?

[zoll]

Re: Starting Point

Also have just purchased a DX6 (http://cgi.ebay.co.uk/ws/eBayISAPI.d...=STRK:MEWNX:IT) anyone know if this charger will work?
http://cgi.ebay.co.uk/2-4GHZ-SPEKTRU...item588439d408

[muchalucha]

Re: Starting Point

ahhhhhh , plnaet 5 planet 5 planet 5 . I may e wrong but i think you will regret pruchasing a spektrum systems. Many people are happy with them but for a first robot i dont personally think its a good idea.

[psycho_fling]

Re: Starting Point

why isnt it a good idea its a great set ?