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View Full Version : [Discussion] Kit Comments/Suggestions



Mike.
04-27-2015, 03:00 PM
I hope it is ok to start this tread... unsolicited opinions, right?!? Everybody has one.

Soft pack Lipo’s are very sensitive to physical damage (indentations or dents from dropping) or deformations (bending). I've got some experience with these types of packs from RC helicopter and competition 1/8 scale off-road racing. I typically would go through a set of packs a season in 1/8 off-road just due to the physical abuse the packs would take from tumbling the car. The outside cells were always the first to go because they took the brunt of the physical abuse. These cells would always discharge faster than the inner cells.

For production kits of the HROS1 I would definitely recommend hard packs if the robot can withstand the extra weight, they are inexpensive enough from places like HobbyKing or other direct overseas sources; there are good reasons why ROAR requires them in sanctioned races. Don't get me wrong, even softpacks can be very durable provided the user is knowledge about the pitfalls.

I would also recommend including a charge bag in the kit for indoor use (however, this does not excuse unmonitored charging). Today’s chargers are doing a better job of monitoring batteries. Definitely use the included battery monitor when the robot is in operation; this is a great included extra to monitor the batteries health. I would recommend putting some heat shrink or something around the unused pins of the monitor to act as insulation. Integrating a battery monitor in the servo board would be even better. This would allow for the possibility of implementing an auto-shut down feature using some depletion mode FET’s just in case the robot is left on unattended. It may also allow for onboard monitored slow charging through the balance port with the FET’s off.

I have noticed that the battery goes from 3.7V to 3.3V unexpectedly fast and seems to charge from 3.3V to 3.7V unusually fast as well. Of course, this may just be that I spent hours working on the Edison over wifi from 4.2V to 3.7V (very low battery drain) and then started using rme and within 10 mins (probably with servos fighting each other) was at 3.3V under load quicker than expected. I still need lots more data points to warren any kind of concern. I'll try to cycle the battery with a good load in the next few days and measure the packs capacity; if it comes near the rating I would have no concern.

Finally, I’m a little concerned about the servo wire routing through the metal frame holes. Only time will tell if this is a valid concern, but I will be keeping an eye out for any wire chafing in these areas. Due to the manufacturing process, the metal in these areas may be sharp, or I should say that I expect it is sharper than the plastic bioloid parts they replace. Not sure what a good solution for this would be, grommets, edging, or wire wrap?
http://www.devicetech.com/products-wire-protection-grommet-edging/spring-fast (http://www.devicetech.com/products-wire-protection-grommet-edging/spring-fast)

Hope this helps,

Mike.

KurtEck
04-27-2015, 05:47 PM
Hi Mike, as I mentioned in the other thread, I was wondering some about getting the battery in to the correct position, such that it is more out of harms way.

I appreciated your comments there and will try to carefully bend some of the harder shrink wrap material as to make it have more length.

I was also debating with myself on plug it in first or plug it in later. I also was nervous trying to plug it which presses the connectors into the side of the battery. But from the other robots, they recommend unplug the battery unless you are using it as to take care of either accidentally turning it on or forgetting to turn it off and over drain the battery. (I have killed a few).

I am hoping the Arbotix Pro has some monitoring of voltages built in and tries to do some things as to as much as possible turn off the servos when the voltage level gets too low. Also hope that it allows the RPI2 or Edison to monitor as well.

As for wiring, I am thinking of using some of the braided cable wrap I purchased earlier when I was building some of the Orion Robotics robots that have sharp metal moving brackets. At that time I purchased a 50' roll of: http://www.grainger.com/product/2RMC7?gclid=CjwKEAjwvPepBRCoqo37teOD1XsSJAC7v6WQ1V fnDWqVazzqeNKje8xP6QOq_zsoiFONsFjNEAs8dhoCVxXw_wcB&cm_mmc=PPC:GOOGLEPLAC-_-Electrical-_-Wire%20Management-_-2RMC7&[email protected]:20150427224035:s
I ordered it from McMaster-Carr (9284K513).

Kurt