I’m prototyping a robot for a class that I will teach next fall. It has mecanum drive (http://www.robotshop.com/en/mecanum-wheel-set.html) powered by your motors: (http://www.robotshop.com/en/6v-285-rpm- … coder.html), and two of these motor controllers: (http://www.robotshop.com/en/10a-5-30v-d … river.html). I’m controlling the whole thing with an Arduino Mega.
I’m powering the Mega with an off the shelf 9V alkaline battery.
My problem is those four motors. How the heck do you guys power them? I’m using one of these 6V, 4.5mAh lead acid batteries (https://www.amazon.com/Rhino-SLA4-6-4-5 … B00G5GXY4C). It performs splendidly. Problem is, it’s HEAVY/BIG/CLUMSY. Is there a lighter alternative that I can use to deliver the same punch? I wouldn’t mind using two smaller batteries if that’s an option…
My second question has to do with a robotic arm that I’d like to mount to the robot. It will be use five of these: (http://www.robotshop.com/en/hitec-hs422 … motor.html). I have 4aa and 6aa battery holders – Can you recommend a pack or rechargeable AA batteries that I can use for the arm? Since both the servos and the motors require 6V, would it be possible to use one battery to power the motors and the servos?
Thank you for your help!
I think the link to the motors didn’t copy/paste well, so here it is again: https://www.pololu.com/product/1573.
I know these motors are 6V…Can I run them with 7.4V lipos?
What else would you suggest?
You should be able to operate both your servo and the 25D gearmotor from a single battery source. Since most rechargable AA batteries are 1.2V, you should probably use your 4-cell holder. That pack should output about 6V when fully charged, which is fine for both the motor and your servo. For longer run times between charging, you should choose batteries with the highest mAh rating you can find (somewhere around 2000mAh is common for AA batteries). The 7.4V Lipo you mentioned is fine for the motor, but you should check to see if the servo can handle that much voltage.
In your post you talk about a 4.5mAh lead-acid battery, that sounds like a typo for a battery like that, it is probably 4.5Ah.
Thank you for sending the updated link for the motor. If you are not aware, you can edit your previous post to fixed the many broken links (Only one is working)
I’ve dug up some NiMH batteries and a lipo, so I’ll give them a try. I only have a 6xAA pack handy, which would give me 7.2V from the NiMh’s. But now that I know that the slightly higher voltage won’t negatively affect the motors, I feel much better about testing those out. Assuming I drive the motors such that they draw 25% of stall current, the four together will draw 6.5A (right?). So a 2000mAh pack should last about 20 minutes of continuous driving, right?
On that note, do you know how much current those batteries are able the discharge continually? Lipos prominently display that info, but finding that data for AA’s is like finding needles in a haystack. Considering the stall current warning that you guys have posted for the motors, I’m wondering: If all other things are equal, maybe I should go with the NiMH if the current they can discharge is limited to a fraction of the motor’s stall current as opposed to a lipo which I understand can throw out almost as much current as these motors would take. Is my thinking off base?
Thank you again for all of your help!
Your 6-cell battery holder will give you almost 9V when fully charged, which is probably too much for your servo to handle and higher voltages can have a negative impact on the motor lifetimes.
You will probably get a little less than 20 minutes, I would think closer to 15-18 minutes. The discharge rates will vary by the battery capacity and manufacturer; you should be able to find some generic discharge characteristics with a brief Internet search, and the manufacturer of the batteries you have might have a datasheet on their website. You might find the information in this forum thread helpful as well.
Please note that with such a high discharge rate, you will probably get a significant voltage drop with NiMH batteries. For high current draw applications like running multiple motors, I personally tend to prefer LiPo batteries for their power-to-weight ratio and high current discharge capabilities.
Regardless of the battery type you use, the batteries will only provide the current that your motors draw up to their maximum discharge rate (e.g. they will not “push” current through the system).