power supply help!

johnproko

i have a robotic arm which is controlled by a bs2 processor. the power supply is the standard 4AA batteries 1,2 volts 2500mamps. when i lift lightweight stuff such as small sponges and a AA battery things are ok. when i try to lift heavy things such as a servo it crashes and restarts the whole process from the start. i tried to power it from a power supply that has 16 volts and 4amps. it can lift very heavy objects but it goes very funny. it shakes and vibrates and i think it is going to explode or brake into thousand pieces...

can anyone tell me what power supply i must use in order to lift heavy loads but also run smooth? there are 5 motors, 2 connected with the same line bottom servos, and most of the times there are 3 servos working ( 2 connected as one, and another one).
if i use a 7,5v and 1 amp plug power supply will it have the ability to lift heavy loads?
for the record i have switched the pin from Vin to Vdd and works smoother but loses the ability to transfer heavy loads from a point A to point B. still does better than the 4 AA battery.
thank you in advance!

Mike Green

Your 4 x AA rechargable battery can supply at best 4.8V to the BS2 and that's less than it's supposed to get. When using rechargable (NiMH or NiCd) batteries, you really need at least 5 cells to get 6V and you need to connect that to Vin (NOT Vdd). Servos are generally happy at 6V, so run them off Vin. You probably will need larger cells (real C or D cells) since servos can draw 1A or more when heavily loaded and you have more than one servo operating at the same time. Personally, I would either use two battery packs, one for the BS2 and any digital circuitry (sensors, etc.) and one larger one for the servos. Alternatively, I would use a 6V Gel Cell battery for everything and make sure the BS2 is running off Vin so there's a little "headroom" for the regulator on the BS2 module. Make sure to use a couple of large electrolytic capacitors across the 6V power supply connected close to the servos (1000uF 10V or 16V) to smooth out the power spikes.

johnproko

if i get a http://www.parallax.com/product/750-00009 for the power supply will it do the job for heavy loading? i cannot understand how much power the servos need and how much the processor.
"Personally, I would either use two battery packs, one for the BS2 and any digital circuitry (sensors, etc.) and one larger one for the servos." connecting one battery pack on the board and the other at the positive of the servos?
thank you for your answer!

johnproko

There is also a 12v 1amp power suply on parallax store. Will it work or fail?

Mike Green

Re Post #3 ... That's not what I said. When you have more than one power supply (for different parts of the mechanism), you connect the negative terminals together at one ground point (usually at the motors where there's the highest current flowing ... see "ground loop" on the Wikipedia for an explanation).

A 12V power supply will damage the servos and may cause the BS2 to overheat. Servos are designed to work with a voltage between 4.8V and 7.2V. The BS2, although it will work with a Vin of up to 9V, really works best (from a heat dissipation standpoint) from 6V to 7.2V, similarly for the Board of Education. Both the BS2 and the Board of Education should work with a 12V supply, but the regulators will produce a lot of heat and may shut down to protect themselves if they get too hot.

johnproko

im really thankful for your reply! im dont know anything about electricity. just good old bs.