Motors

joey_picus · Post by **joey_picus** » Fri Apr 23, 2010 10:02 pm

To put it simply, speed and power

they've become almost universal since people started using them, at RRC 20 only about two or three ants were using servos for drive.

http://www.youtube.com/watch?v=JUJTEw6iWTU is the first video I can find that demonstrates it, although a search for 'Antweight World Series' or 'Reading Robot Club' on Youtube throws up quite a lot of videos with both geared motor and servo robots. Terrior uses gearmotors, Valliant used servos in that incarnation, and the differences in speed and torque are obvious even with larger wheels on Valliant.

Aside from the speed and power I also find it easier to attach wheels directly to them as they have a 3mm D shaped shaft as opposed to a splined servo shaft, and you can get mounts and wheels specifically for the gearmotors which work very well for very little weight. The only potential disadvantage of gearmotors I can think of is the complexity, and possibly if you happen to find some servos that come with their own RF shielding although with 2.4ghz that's not an issue.

Post by **BeligerAnt** » Fri Apr 23, 2010 10:11 pm

Geared motors have metal gears which are much stronger than the plastic ones in most servos. Many metal-geared servos do not have a full output gear, so cannot be used for drive.

Servos are designed for high torque, so have high-ratio gearboxes. Hence they are slow. Motors are usually available with a range of gearboxes so higher speeds are possible.

Speed controllers give better proportional control than modified servo boards. Also speed controllers are designed for continuous operation. Servo boards (especially the smaller ones) are not really suited for continuous operation and burn out after a while.

The biggest driver is usually speed. Whilst the Park HPXF servo appears to use a very similar motor to the Sanyo/Technobots motors, the gearboxes are completely different.

Philip · Post by **Philip** » Sat Apr 24, 2010 7:37 pm

Thank you. The video demonstrated the difference quite well.

If I used motors, such as the Pololu 30:1 Micro Metal Gearmotor (High Power), what speed controller would you recommend? I don't need a weapon switch on the speed controller.

Post by **BeligerAnt** » Sat Apr 24, 2010 9:49 pm

The Sabertooth 2 x 5A controller is popular and more than man enough for any antweight application:
http://www.technobots.co.uk/acatalog/Sh ... r_530.html
(probably also available from other suppliers)

The old Scorpion Minis were good. There is a new version out now which I don't know much about, but probably worth considering:
http://www.robotpower.com/products/scor ... _info.html
(you don't get mixing with the Scorpions, and you need one for each motor)

Not sure whether the Barello Ant 150 boards are still available.

The cheap solution is to use the control boards out of cheap standard-size (45g) servos. These can often be found second-hand at your local model shop, or bought quite cheaply on ebay. They are capable of driving the Pololu motors, but the control is not quite so good as a proper speed controller.

knightrous · Post by **knightrous** » Sun Apr 25, 2010 2:41 pm

Philip, check out http://www.robotgear.com.au/
They have full range of the Pololu gear motors and at decent prices.
I'm about to order a few gear motors myself to try out

Philip · Post by **Philip** » Sun Apr 25, 2010 7:43 pm

Good find, Aaron. Thanks for your advice, Gary.

Which wheels go best with Pololu motors? Would the Pololu Wheel 32 x 7 mm 3.4g be good for ants?

joey_picus · Post by **joey_picus** » Sun Apr 25, 2010 11:54 pm

They work well enough on Jigsaw at the moment, it won the speedway event at RRC 20 last month

they stay on the shaft well and are very durable as long as the tread doesn't get hit by sharp blades (as Dave found out with Little Devil)

They are on the narrow side but depending on your design the lack of traction might not be much of an issue.

peterwaller · Post by **peterwaller** » Mon Apr 26, 2010 7:51 am

Philip I see from the previous page you were looking at the Pololu 30:1 HP motors. You might find them a little fast as the HP motors are around twice as fast as the same ratio standard motors so you might do better with 50:1. I know you don't have to run them at full speed but you might as well have the extra torque and more control. Here is a comparison of most of the motors from my website.
http://www.antweightwars.co.uk/MotorSpecs2.pdf

Philip · Post by **Philip** » Mon Apr 26, 2010 9:02 am

That is a handy table, Peter. Thanks.

It is good to hear that you had positive results, Joey.

alasdair · Post by **alasdair** » Tue Apr 27, 2010 5:02 pm

I have a new Q concerning motors. Does anyone know where to get really torquey, 50:1 motor that could preferably power a 100 gram axe?
Yes, you heard correctly. 100 grams. 8)