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Battery and Power
Regulator Background
BEC's are used in remote control airplanes so that 2 battery packs are not required. Good [background info] (http://www.dimensionengineering.com/info/bec)
Battery Physics
Contacting dimension engineering to make sure it fits our needs
Note, a 12C pack at 3100mAh, results in 12x3100 = 37200mAh = 37.2 A is max discharge rate. Good thread
Battery Operation Guideline, recommended batt source
This battery was bought.
- Net Weight 360
- Gross Weight 401
- capacity (mAh) 2200
- max cont. discharge (C) 30
- max burst discharge (C) 60
- max cont current (A) 66
- max burst current (A) 132
- Series (S) Parallel (P) 6S1P
- Length (mm) 104
- width (mm) 35
- Thickness (mm) 43
- wire gauge 12
- balance connector type JST-XH
- connector type 4.0mm Banana Connector
- Vol. Gap 22.2V
- IR (mohm) 35
- Wire length (C/D) cm 4/9
THE BELOW WAS NOT PURCHASED B/C COMPANY WOULD NOT SELL IT
Attempted to buy 22.2V, 2.5 Ah for the following reasons:
- It can discharge a maximum 5A which will service all 6 motors running @ .4nM, which Greg calculated to be the torque required for a leg to stand the robot up. The current drawn by the motors is proportional to the torque the motors supply using the conversion factor, 25.8 mNm (A^-1)
- Event though the motor is rated for 24V, lowering by 1.8V, reduces the power to the motor given a fixed current, yet its anticipated extra current will be drawn to offset this.
- If our robot weighs 4.66kg, the battery will comprise 8.3% of the robot's weight, which is in the range of the EduBots Section 3.3 ratio.
- Energy density is 144.23 Wh/kg, which is slightly less than the EduBot, (158 - 187)
- This charger was also purchased, should charge in 2hrs.
/#workinOnTday
The motors will be wired in parallel and fused individually(I've emailed Maxon to see if a particular fuse is preferred) to provide the greatest protection. We can insert a "By-Pass" capacitor near the power source if we find we are getting too much high frequency noise, Radd has these.
For the CPU, The decision was made not to get a USB battery pack because of additional weight concerns and reading this article. Instead, we will start off using a voltage regulator from our battery, which is a simple, lightweight chip I have experience using. If it turns out that the motors cause too much voltage fluctuation (which cannot be filtered out by the regulator), then a separate power source must be used as the BeagleBoard (and any logical unit for that matter) is very sensitive to voltage levels as this is how logic is expressed.
This place seems to have similar batteries to the other sites but much cheaper: http://www.hobbypartz.com/
We'll need to buy a battery in the 12-24V range to supply our six motors. We also need to figure out if we need a second battery just for the CPU, or if we can figure out a way to combine them.
We also need to think about fuses and how that's going to work. The motor controllers probably require a certain type of fuse, which we should look into.
For battery type, it looks like lithium ion, lithium sulfate, and lithium polymer have the highest energy density. Nickel based batteries are about 2x less.
Custom Polymer Li-Ion Battery: 22.2V 2500mAh (56.25Wh, 5A rate) with PCB (4.5):
http://www.batteryspace.com/Customize-Polymer-Li-Ion-Battery-22.2V-2500mAh-56.25Wh-5A-rate.aspx
- 390g
- 10A PCM
Custom Li-ion Polymer Battery: 22.2V 3Ah (66wh) 30AR w/ PCM & 8" Open Wire Leads (CU-MM146 PID# 5398) (5.4):
http://www.batteryspace.com/Custom-Li-ion-Polymer-Battery-22.2v-3Ah-66wh-30AR-w/-PCM-and-8-Open-Wire.aspx
- 650g
- 40A PCM
Potential x6 fuse box, compact with attaching holes:
http://www.delcity.net/store/6!way-standard/p_10959.r_IF1003?gclid=CJD9p-qu97MCFQyk4AoduikA2Q
- $4.55
- 65 amps max