Questions/builds thread.

**Ellis** · 26th August 2011, 13:00

Hi all.

Instead of making 98,056 threads or posts to ask nooby questions, I'll put them all here. I'll use this as a build thread too.

I have no access to a machine shop and very limited money, so I'm using chopping boards as against to plastic bought online, metal of all types from just around the house, etc. I bodge things, sadly robots must be bodged too.

I am quite far down the line of building a featherweight box. I can't use it to compete because I live in Spain, so for now it will literally be a box with 4 drill motors, 100mm blue wheels and the fewest electrical components possible. I'm not going to bother with kill switches or what have you, I don't see the point yet.

I'm also hoping to piece together a drum spinner beetle. I have the ideas and some raw materials. I know what components I am likely to use but, my first question is this...

Is there any particular reason not to use batteries from phones? They're low volts, just 3.6v normally, but I have one sitting in front of me that is tiny and claims to be 930mAh. What's the consensus? Stay away? Good idea? Never used before? I have many more questions but that's the main one for now since they're cheap and readily available, let alone tiny!

Thanks.

Ellis

**Ellis** · 26th August 2011, 16:39

I've just realized how hopeless a question that is. Ignore talk about phones! I'm just starting to get into Li-Po and brushless motor talk and it's all very confusing. I thought Li-Po batteries and chargers would be far more expensive than they are. Again, sorry for making such a confused introduction.

I'm likely to have Li-Po and Brushless motor questions soon. Brace yourselves! I'll try and be as light on you all as possible. :wink:

**Ellis** · 28th August 2011, 14:27

Hi, quick question... is there much of a difference between inrunner and outrunner brushless motors? I seem to see more outrunners in robots, is that for a reason?

Thanks.

**typhoon_driver** · 28th August 2011, 15:08

inrunners are similar to regular dc motors in that the inside rotates, outrunners, the outside rotates. The outrunners generally have a lower kV rating so have greater torque and lower final rpm meaning less gearing is required.

Don't look at using batteries from phones etc as these are low discharge devices and so the battery isn't designed to deliver the high currents that a drill motor requires. Chances are you would get nothing more than a very toasty battery potentially leading to a fire.

**typhoon_driver** · 28th August 2011, 15:13

I would like to add that the kV rating tells you how fast the motor will rotate at a given speed. Multiply the number of volts through the motor by this number and you will get the final number.

Also, if you are using standard speed controllers then these will generally come with failsafes. ALWAYS build a robot with failsafes. A 30lb ramming bot with 4 drills could break your ankle if it got out of control.

**Ellis** · 28th August 2011, 19:43

I made this thread only a few days ago but since making it I've learned a lot when it comes to brushless motors and Li-Pos. I'm aware that the whole shell of the motor spins on an outrunner as against to a more traditional inrunner style motor. I meant (maybe I should have specified) that if in power to weight, or cost, or if they're different in any sense like that. I see mainly outrunners in robots and wondered if that was for a reason. Thanks for the info, interesting to know inrunners generally have lower kv...

Also aware that phone batteries or anything similar is barmy. I've understood how Li-Pos work now (or enough to know phone batteries are pretty useless!) and having realized that Li-Pos are relatively cheap and that I need a high enough C rating, the right number of cells/volts, etc, I'm comfortable with simply buying some.

On a different note, today I sat down with my dad today and we begun the plans for the featherweight box. We're looking into a four-bar lifter and how something like that could fall into our design.

Thanks for the help, I'll keep this thread updated!

Ellis.

**typhoon_driver** · 29th August 2011, 20:18

Good good, this sport is all about learning

**Ellis** · 3rd September 2011, 16:50

Hi again.

So, I'm tempted to run at 18v instead of 12v. Reason is, I'm likely to use a drill motor for a lifting mech, and I happen to have a 14.4v drill laying around. Installing 14.4v for the lifter motor and using a separate set of batteries for the drive seems over complicated and pointless.

To get more torque and speed out of both the drive motors and the lifter motor, I want to run 18v. I've looked around and I'll probably get an 18v drill battery or two. That's all straight forward.

The problem is, if I choose to run 18v to power the drive, I'm not sure how my ESCs will like it? I've got 2x 12v drills on 30a Electronize each side. Will 2x 12v drills on 18v draw too much for my ESCs? Thanks!