Hello I’m building a full scaled size styrene R2D2. I’m currently designing the feet and I was planning on purchasing the Parallax 7.2V Motor, Bracket and Wheel Kit to utilize. Would it be ok to use a 12v 15A SLA battery where the motors are connected in a series? Or is there other battery options I should use?
Thanks Ryan.
My guess it would weigh around 30-40lbs. I might try the NiMh option (6-1.2V NiMh batteries each with 2.4Ah).
Ryan.
I wasn’t going to have anything else connected to the motor batteries (lights independent battery connected in the dome). If you connect the 6 1.2v batteries in series would they total 7.2v 14.4Ah? Would you get a longer life on your battery running time.
Thanks Ryan
I just weighed my current parts and made an estimate on parts to be made (ie legs, ankle and feet), would the 7.2v motor bracket and wheel kit support 40-50lbs of weight? I was also going to place on each of the two outer legs omni foot stabilizer for balancing the weight distribution. I want to make sure my R2 is not too heavy for this motor kit. The description says it is perfect for small to medium sized robots (I’m just not sure where mine fits within this criteria).
Thanks Ryan.
How much will your full scale R2D2 weigh? You are correct in that the kit looks like it will be a good option. Note that the motors operate at a nominal 7.2V whereas you specified using 12V batteries - it would be better to use 6V (closer to 7.2v) rather than a 12V.
An SLA is quite heavy, but should last a long time (15Ah). The other option would be a bunch of NiMh batteries - it would cost you a lot more but weight a lot less. Also, you can get 7.2V exactly using NiMh batteries. The last option would be to use LiPo (7.4V) which would weigh even less than NiMh but cost even more.
Two motors will consume about 0.5A to 1A each, but then there are losses (DC gear motors are not incredibly efficient), also there is the draw from the microcontroller, lights and any other actuators you have connected to the robot. 2.4Ah might last you about 30 min to 1 hour.
6x 1.2V, 2400mAh cells in parallel = 7.2V, 2400mAh pack
In theory if you connect two 7.2V, 2400mAh packs in series, you would get double the operating time (4800mAh).
50 lbs is no longer “medium” - you are in the “heavy weight” category. Are you also considering the weight of the battery?
You’ll likely need larger gear motors, especially if you encounter even a small slope. Consider:
2x robotshop.com/planetary-gearmotor-720rpm.html (watch out for the 14.4V voltage)
2x robotshop.com/banebots-4-1-p60-gearbox-rs555-brushed-motor-kit-4.html (at least 16:1)
Consider the Drive Motor Sizing Tool:
robotshop.com/dc-motor-selection.html
For control, you’d need at least a 2x25A controller with protection.
