Speed?

[thebeardedone]

Hi there,

I have a question regarding the speed of the motors.

I am looking two possible motor choices:

1) Modified SuperTec HPX F/BB
@6V
Transit time = 0.05
RPM=10/0.05=200

So, I can work out that the RPM of this servo is 200, so using a 1.5" wheel that means that the speed equates to 15.7in/s or 29.87cm/s.

That seems to be a reasonable speed to me and the torque is quite high (3.6kg.in). I would be using four of these.

2) Pololu 50:1 HP
@6V
Unloaded RPM=625

Using a 1.5" dia. wheel means that the speed is 49.07in/s or 124.63cm/s. This seems to be incredibly fast. Maybe even too fast for my requirements but it could be limited by other means. The torque is also low on these pups (1.0Kg.in). Once again, I would be using four.

So, based on these figures I wanted to know how much the 150g weight will be a factor in reducing the speed of these motors.

Also, what is the size of the ant arena, so that I can work out some travelling figures and what is the base material?

Finally, this is going to be a push bot so it is important to have the torque for pushing out the ants? I appreciate that the ants are low weight and that 1.0kg will be plenty of torque for getting an ant out but then the speed would mean that control was an issue (for me anyway :p). I also understand that there are other factors that I need to consider before I can make a real decision (coefficients of friction, how much torque my wheels can take before they just spin etc) hence why I am questioning the arena base material.

Regards,
Sam

[EpicentrE]

Regarding speed, I always aim for around 1.2m/s+ top speed for my ants, and nothing below 1m/s if possible. Some of the faster robots go even faster than that. The trick is learning not to always drive at full throttle, otherwise yes, it can become uncontrollable, but having the speed there if you need it can give you a big advantage if you need to outrun another fast robot, circle a spinner, or get out of a sticky situation.

Regarding torque, I've never seen any motor used for antweight drive stalling. With the small weigh of the robots, it's simply not possible to get enough traction with wheels to cause the motors to stall, they'll just wheelspin instead. Using smaller-than-standard motors (such as geared pager motors) or tracks might make it possible, but even then I'm doubtful. Pushing power in ants is pretty much dominated by how much traction you can get (wheel width, tyre material, wheel spongeyness, etc) and the distribution of weight within the robot (more weight over the wheels is always better, but have too much weight too far back and you risk wheelying), not by the torque of the motor.

[thebeardedone]

Hmm, I can see why the extra speed would be useful, Scott.

So, the servos in terms of metres come in at roughly 0.4m/s whilst the motors are roughly 1.24m/s. Still seems really fast to me.

Any videos of ants reaching this speed in an arena?

Regards,
Sam