gimson gro2 18volt motors

[chris knee]

hi guys, what would hapen to these motors if i ran them on 24 volts, also to get 24 volts of power do i just wire two 12 volts together
thanks

[plargen]

Re: gimson gro2 18volt motors

they might withstand it, some people run theirs on 18v and they seem to run ok but it might be worth putting a heatsink on the motor possibly with a fan

oops sorry thought they were 12v for some reason

[typhoon_driver]

Re: gimson gro2 18volt motors

Ok lets back it up and start with the basics. Power is not measured in volts. It is measured in watts. We get the number of watts that a motor will output by multiplying the voltage by the current going through it. This can be tricky to get a measured value for so the general rule of thumb that I and several others use when it comes to electric motors is to only run them at 1.5 times their rated voltage. So in theory an 18v motor could be run at 27volts in a robot and should have a reasonable life.

Do a bit of background reading into GCSE or standard grade electrical circuit physics and you should get most of the answers you need (that's right, that stuff was actually useful!)

And with your second question, 2 12v batteries connected in series will give you 24v

http://electronics.howstuffworks.com/ev ... ttery6.htm

[maddox10]

Re: gimson gro2 18volt motors

I like to use an example.

Volt/resistance (ohm)=Ampere
Volt*Ampere=Watt

An avarage brushed, Permanent Magnet, Direct Current motor has an efficiency of 80%. Meaning, for every 100W flowing trough, you get 80W of drive-power, and 20W of heat.

Now, increasing voltage does 2 things. It increases the amount of amperes that can flow, and in a PMDC it increases RPM according the voltage increase. (double the voltage,and the RPM doubles too)

************************************************** **************************
So, lets see. The Gimson GR02 18V motor runs unloaded, after gearbox, 810RPM@18V, or 1080RPM@24V

Depending on wished speed, you'll decide wheelsize. Not many options if you use commercial wheels.
80 -100-125-mm from Robochallenge.
To make it easy.
80mm wheel @18V=12,5Km/h @24V 16 km/h
100mm 15km/h 19km/h
125mm 19km/h 25km/h

But here's the rub. Powerconsumption increases with speed.
The difference between 12km/h and 25km/h will be about 4 times more power needed .
So, 18V 2A will become 24V 8A (this is a guestimate of normal, non fighting powerconsumption)
With that 80% efficiency avarage we get
18V*2A/100*20= 7.2W of heat.
24V*8A/100*20=38.4W of heat.
As long the fan in the motor can keep air flowing, the motor can handle it. BUT
In a fight you'll have conditions that increase powerconsumption. From full forward to full reverse is the most heavy - this is also the moment were the less well build and engineerd mechanical driveparts will fail-

But the worst case scenario is stall. (stall means the motor is powered, but can't turn)
Zero speed, max amp draw. Efficency 0%. Even with a good current limited speedo the motor will heat up fast.
25A current limit is for most drill powered feathers enough. (the Gimsons are very nicely enginered batterydrill based drives)So, at 18V 25A, you're having a 450W heater, on 24V it's 600W.

In non current limited speedo setups, it's the question what will fry first. The motors, the speedo or the battery. Most of the roboteers have seen it all before.

[chris knee]

Re: gimson gro2 18volt motors

wow that was interesting reading, i think the best thing to do is stick to what it is meant to be run at, you guys certainly know your onions.......thanks

[typhoon_driver]

Re: gimson gro2 18volt motors

Lol when you can start to measure the time you have been in a hobby in decades (well over 1 decade) then you pick a few bits and pieces along the way

Actually if you want a good book to start yourself off then get this one here,

http://www.amazon.co.uk/gp/product/0954 ... 02_s00_i00

It was written by the team captain of team typhoon and covers a good deal of the theory behind a lot of the different parts of robots. Also a good bit of theory on spinning weapons. Only second hand copies kicking about these days as only 1000 were made

[maddox10]

Re: gimson gro2 18volt motors

wow that was interesting reading, i think the best thing to do is stick to what it is meant to be run at, you guys certainly know your onions.......thanks

If you stick to the known things, innovation dissappears.

On the other hand, understanding basic parts helps avoiding unpleasant surprises.
So, do you feel innovative and can cope with magic smoke, please try.

In short.

Time*funds*creaticity= Active combat Robot.

[chris knee]

Re: gimson gro2 18volt motors

im trying but i must admit i am finding it harder than i thought......wish my boy took up train spotting or stamp collecting now lol, on the up side it is giving me a bit of education, and at my age that aint a bad thing