[...] so that I can save some money on postage and buy it together with the smaller motors and other things.
I don't know how shipping within England is priced, but they had to know the total weight of what I bought before they could tell me the shipping price (and they sent it in two separate boxes :-/). So there may or may not be a saving in getting it all at once (depending on national rates).
I just tested one of the motors and it won't start running at anything less than a setting of around 1..2A, but that may be the foldback current limiting of the PSU I used, as it dumps the voltage to close to 0V on over current draw.
It starts reliable at around 0.7V, as long as it's allowed the current it needs - stall current is around 2.5A to 3A at 0.7V.
At 3V, you cannot stop the axle with your fingers without getting a friction burn and it can take 12V just fine (but I'd add a temperature sensor if I was to constantly overdrive it).
I am still going to use the smaller motor for my first experiments and bots - learn from it and than go onto something bigger. Hope I have cleared this up. So what batteries should I buy ?
All cleared up
Since the larger motor accepts a higher voltage and the controlling element (transistor switch or whatever) will have some small voltage drop, not forgetting the discharge voltage range of the battery, I'd go for 10 AA's
, which would be from ~14.5V fresh out of the charger, down to ~9V (at that high a current, ~11V on low current draw).
This will ensure full speed until the batteries are discharged and using PWM, you would get 9V from the fully charged battery by using a duty cycle of 62%
For the 6V motor, 6 NiMH AA-cells
will give you from ~8.7V down to around 6V over the discharge life of the cells (again depending on discharge rates), with a duty cycle of 69% to get you 6V initially.So, 10 cells for the large motor and 6 cells for the 6V motor is my best recommendation.
If you search a couple of R/C-sites, you might find battery packs with an equivalent number of cell at lower prices and/or higher capacity, but stay off Lithium based batteries (anything starting with "Li") until you know enough about them to stay safe.