FAQ
Over the years, I have received many questions from micromousers all over the world. Here's a list of the frequently asked questions and answers.
Questions
Q1. Is a lighter mouse better?
Q2. How does the width of the mouse affect performance?
Q3. How do you make use of the gyroscope?
Q4. How can your mouse make what is apparently the same curve turn even at higher speeds?
Q5. What is the relative importance of straight line speed, turn speed or acceleration?
Q6. What do you use for your micromouse tires?
Q7. Is a bigger or smaller wheel better?
Q8. Where do you get your parts?
Answers
Q1. Is a lighter mouse better?
Grip wise, a heaver mouse will be able to exert a larger force on the floor, since the grip of the tires is about proportional to the weight of the mouse. However as a heavier mouse needs a proportionally larger force to accelerate the same amount, in the end the lighter and heavier mouse have no difference in terms of acceleration. This is provided the motors are powerful enough.
What would be more important is how the mouse is balanced. Ideally, the cg of the mouse should be over the drive wheels. This allows the maximum amount of force to exert by the tires since the grip of the tires is proportional to the force pressing down on it. In addition, if the heavy parts of the mouse are very far away from the centre of rotation, this makes the mouse sluggish during turns.
Q2. How does the width of the mouse affect performance?
A mouse that is very slim would be less stable in the curve turns, since what happens is that the weight transfer is greater and the inner wheel loses grip faster. This limits the speed at which the mouse can turn. However a slimmer mouse has more allowance during a diagonal run. In addition, during a V-turn my mouse comes to about 5mm from the pole. This is not a lot and thus my mouse cannot be too wide.
Q3. How do you make use of the gyroscope?
Basically control of my mouse has two sections, a translational position PD control loop and an angular position PD loop. In making use of the gyroscope, basically the angular velocity is read from the gyro rather than from the differential velocity of the motors. However the gyro null point tends to drift thus it is important to read off the null point just before the run. During a short fast curve turn the drift is acceptable. On straight runs the sensor data helps to compensate for drift.
Q4. How can your mouse make what is apparently the same curve turn even at higher speeds?
During the curve turn, the radius of the curve is dependent on the angular velocity of the motors and the translational speed. As the mouse turns faster, the maximal angular velocity must be increased proportionally. The mouse should cover the same distance irregardless of the turn speed.
As the turns get faster, my mouse routinely exceeds the traction limit of the tires. The result of this is that my mouse will drift sideways as it turns faster. To compensate, I turn earlier as the speed increases.
Q5. What is the relative importance of straight line speed, turn speed or acceleration?
I would think that the most important is turn speed. The mouse routinely makes a lot of turns during it speed run and a higher turn speed helps to maintain a higher average speed. After which is acceleration and the maximal straight line speed.
Q6. What do you use for your micromouse tires?
I used to use table tennis rubber. I found it easier to use the inner layer, which gives a fairly good grip. Quite a few of the top Korean mice used the inner layer. Of course, the outer dimple layer is peeled off.
Nowadays, I use Linatex rubber. However on my newest mouse Min4A I actually use the tires from a small rc racing car called Mini-z. Idani was generous enough to give me a sample of the mini-Z tires he was using and that's how I started using it.
Q7. How do you determine your wheel size?
For stepper mouse, the wheel size is very much determined by the stepper motor size since the wheel is normally directly mounted on the motor shaft. Thus the wheel needs to be big enough to accomodate the motor size.
For DC motor, it's much more complicated. If tires are too small, the uneveness on the floor will be more pronounced. Big tires will ride over the small hump. Another big advantage of big wheel is that the amount of dirt/surface area pick up is less, which can affect mouse reliability greatly.
But if the wheel is too big, the c.g. of the mouse is likely to be raised. The wheel moment of inertia is likely to be higher too, unless special care is taken to lower it.
Q8. Where do you get your parts?
I obtain my parts through local shops or distributors in Singapore. For the international brands you might be able to find a local distributor if your not from Singapore.
Motors: Manufactured by Minimotor SA.
Local Dealer:
uia_pl@pacific.net.sg
Gears: KG stock gear
Local dealer:
Tripod Trading Pte Ltd
10 Dickson Road Singapore 209498
Mr Edwin Tan
Tel: 6295 0933
Fax: 6295 0233
Linatex Rubber as well as wheel manufacture and bearings
Shinko Bearings & Beltings Pte Ltd
803 King George's Avenue #01-140 Singapore 200803
Mr Jason Ng
Tel: 294 2493/ 294 6263
Fax: (65) 298 1309
LiPo Batteries
Singapore Hobby Supplies Pte Ltd
An alternative source would be WorleyParsons Singapore representative.
Screws
Pan Sun Hardware Pte Ltd
Blk 803 King Geroge's Ave #01-174
Tel : 2963180