New Roboteer!

[ajw]

I don't know if someone could offer some advice, but I've just been testing a couple of 300rpm 9g gearmotors from China driven by 9g servo boards off 6V nimh, and without creating a chassis to mount them on they appear to be running slower than I expected. Just wondering what you guys' experience is with these motors, for example what wheel diamter you use? I'm beginning to wonder if I should have bought the 540 rpm models or whether I should drive them with a higher voltage from a different controller? Cheers

[Remote-Controlled Dave]

Jim (earthwormjim) had a similar problem. Are they the cheap motors? I think they might just be poor quality. When he switched to the more expensive "official" types, the problem was cured.

[ajw]

Thanks Dave, yes they're the cheap ones from ebay. Having said that the motors could well be going 300RPM and I'm just used to the speed of speed hacked servos so I don't want to do the motors an injustice if they are in fact performing to spec. Looking at my servo driven ant, it seems to move at about 1m/s and that's with a wheel circumference of about 8.5cm. I guess from this that it's moving at about 700RPM assuming no tyre slipping. Would that be roughly correct or is this theory nonsense in real life?

[peterwaller]

I have used quite a few of the cheaper ones and not had any problems.
If you are using servo boards to drive them presumably they are running at 5V which makes quite a difference.
If we assume the motor is 10 ohms to keep the maths simple then on 5 volts it will take 0.5 amp and you will get 2.5 watts power.
If we go to 8.4 volts the motor then draws 0.84 amps giving 7 watts which is almost three times as much.
The HP motors are 4 times as powerful as the standard ones but the cheap ebay ones seem to be the same as the standard ones.

[ajw]

I'm running them off a 6V nimh, I'm assuming that's what the PWM pulses from the servo boards are too. Thanks Peter, that makes sense, I've ordered a couple of 540rpm ones as well to have a play around with as for the moment I'll be sticking with 6V. Hopefully will have at least one new ant by AWS37.

[earthwormjim]

Yo,Yo.
I bought 300,400,and 540 rpm cheap chinese motors from ebay,and then some 50:1 hp ones.
On 30mm wheels,the 540 rpm,and the 50:1 hp's were pretty quick.But the cheapies were easy to stop with one finger.Not much power behind them.
IMHO,speed wise they would all be useable in an antweight arena.The faster ones I am running at 50% speed for turning,as they are a bit lively!
The main difference is certainly the power.
Laters. 8)

[ajw]

cool thanks Jim, I guess I'll just experiment and see what gives the best results once I have something resembling a chassis. This'll be for the second of two robots if I get a chance to build it before the AWS.....running out of time!!!