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Andrew_Aitchison

min lipo rating for consistent range on full auto?

What kind of spec of lipo would  need for a full auto blaster of 9 darts per second, to keep consistent range on each shot? Basically I know I need higher current for faster spin up time. Just not sure what the minimum requirement would be.
OldNoob

Take the motors you are using, read their STALL current off the data sheet, if you have a generic robot motor as your pusher, assume less than 5A, multiply STALL CURRENT by 1.3. The result is the minimum BURST discharge rating. Example 3x rhinos @8A each stall= 24 x1.3= 31.2 so you can have a 20c constant with 30c burst and that would have to be over 1000mah capacity.
BSUK has recommended packs on its site and there are specs in The Vault on the motor/battery combo spreadsheet.
SSGT

As noted it'll depend on the motors. It's also worth noting that a pack capable of supplying more current will not make a motor produce more torque (if the current pack is already appropriate) nor will it force more current through the system. 3 Rhinos on 3S will perform the same (differences in internal resistance between chemistries aside) regardless of whether the pack can supply 50A or 500A as the motors will only draw the current they require at a given moment in time. The current drawn is related to rotor speed since the back EMF generated increases with speed and opposes the supply voltage (Lenz's law) to reduce the armature current (Ia=(V-Eb)/Ra). Under load the motor spins slower, less back EMF is generated and more current is drawn (the maximum being the purely resistive stall condition).

If the motors have a total stall current of 40A then it's a good idea to spec your pack so that it has a burst rating of at least the same (ideally with an additional factor of safety - the 1.3 in Oldnoob's post but you can vary this depending on experience, pack brand/reliability etc.). It's not necessary to spec the continuous current of the pack to match the stall current of the motors since the motors should never be drawing stall current for more than a fraction of a second in normal operation, and no more than a few seconds in the event of a hard stoppage (burst ratings tend to be for 10 seconds - if a pack is rated to 35C burst with a 2200mAh capacity then it should be able to supply 77A for up to 10 seconds).

In short, you should spec the pack to meet, or exceed, the transient load placed on it by the motors. If you need more torque, and the pack can already supply enough current to meet the demands of the motors, then you need more powerful motors. Boff's motor/pack combo spreadsheet is here and the individual datasheets for most motors have been complied in this spreadsheet.

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