http://cgi.ebay.co.uk/9-6V-3700mAh-NiMH ... 33572d80baI have four 18v drills which need to be powered by 18v batteries, but I can't find any at the moment nimh wise.
Two packs of these connected in series will give you 19.2V and a decent running time.
Technobots for the LED. They do 12V and 24V ones that contain internal resistors, so you can just connect it directly to your battery supply. If using the packs above at 19.2V, get a 24V LED. They also do a selection of sizes of silicone wire that you pay for by the metre. Relatively cheap too.I need an led + resister, power switch and wiring.
For a power switch, just use a pair of Deans connectors and a small loop of wire. GiantCod has 10 pairs for £4, which is good value:
http://www.giantcod.co.uk/deans-style-u ... 03931.html
Without delving too much into physics, the equation for Power is Voltage x Current (P=IV). When you apply a voltage to a motor, the motor draws current (amps) from the source (aka a battery). This combination of volts and amps gives you power, which is visible to the eye in the form of the motor spinning. If you know the power rating of the motor, you can work out how much current it will draw when you apply a specific voltage to it. Rearranging P=IV to calculate current gives I=P/V.But I don't understand speed controllers, I mean I know how they work, I just don't understand what the max ampage etc. is talking about. Is that the maximum drain from the motor on the battery? Or is that the maximum ampage it'll let the motor drain?
Taking a Bosch 35 motor as an example; the motor's maximum power output is 35W and you want to run it at 12V. The current (I) is power divided by voltage;
So 35/12 = 2.91
This means your motor will be drawing 2.91A when running at 12V.
However, this is only when the motor is at its most efficient, i.e. it is spinning at a constant speed without any load being exerted on it. If you attach a wheel to the spinning output shaft and then create resistance by, say, pressing the wheel against a surface, you are applying a greater load to the motor, and it has to draw more current in order to maintain the power output. So when your motors are in your robot, they will draw more current when you try to push another robot than they will if you are driving along unimpeded in a straight line. Your motors will also draw more current when accelerating from a standstill and when changing direction rapidly.
Often during these instances, the current draw can spike up quite high for short periods of time. A figure of 4x the normal current draw is a good estimate of what the motors can be drawing. So if your drill motor draws 10A under normal conditions, then it could be seeing as much as 40A when rapidly changing the motor from forwards to reverse.
So when it comes to choosing a speed controller, you need to pick one that will be able to handle the amount of current being drawn from the battery by your motors. I like to use 10A as a standard current draw for drill motors (although this varies between each motor and could either be more or less), so you want a speed controller than can take at least 10A continuous, with the ability to handle higher currents for short (1-2secs) periods of time.
It's best to over-spec the speed controller slightly so that it's not performing right on its limits all the time. With the 10A example, I would use a controller with a 15A continuous current handling capability. Most speed controllers can cope with the larger bursts of current for a limited time but if you pull the high (stall) currents through your controller for long periods, that tends to be when the magic smoke comes out.
- FRA
- Forum
- Robots
- Events
- Media
- What's New?
All times are GMT. The time now is 06:21.
Reply With Quote
Bookmarks