Comments on: Wheel assemblies for Decimus 2 http://www.micromouseonline.com/blog/2008/01/10/wheel-assemblies-for-decimus-2/ A micromouse builders blog Tue, 06 Jan 2009 15:11:54 +0000 http://wordpress.org/?v=2.3.3 By: peteh http://www.micromouseonline.com/blog/2008/01/10/wheel-assemblies-for-decimus-2/#comment-236 peteh Thu, 07 Aug 2008 22:51:25 +0000 http://www.micromouseonline.com/blog/2008/01/10/wheel-assemblies-for-decimus-2/#comment-236 They are 6 Volt motors. Even if you ran them at a full 7.2v, they would be fine with the loads presented by a micromouse. A couple of things make the voltage relatively unimportant. First, there will be some loss in your motor driver so you may well not get as near to 7.2 V as you think. Second, these motors are very overpowered for a micromouse and you may find you never get to run them at full 100%PWM. Or not for long anyway. Acceleration from a standstill only needs about 0.75V. Do the sums, that really is all. Worst case is acceleration/deceleration while running at top speed. Then you may need all of the battery voltage to get enough current through the motor because of the back-emf generated by a turning motor. To summarise ... The motors rarely run at full voltage. Even then it is not for long. They never get warm to the touch - they are horribly overpowered. They are 6 Volt motors. Even if you ran them at a full 7.2v, they would be fine with the loads presented by a micromouse. A couple of things make the voltage relatively unimportant. First, there will be some loss in your motor driver so you may well not get as near to 7.2 V as you think. Second, these motors are very overpowered for a micromouse and you may find you never get to run them at full 100%PWM. Or not for long anyway. Acceleration from a standstill only needs about 0.75V. Do the sums, that really is all. Worst case is acceleration/deceleration while running at top speed. Then you may need all of the battery voltage to get enough current through the motor because of the back-emf generated by a turning motor.

To summarise … The motors rarely run at full voltage. Even then it is not for long. They never get warm to the touch - they are horribly overpowered.

]]> By: Siddharth Chinoy http://www.micromouseonline.com/blog/2008/01/10/wheel-assemblies-for-decimus-2/#comment-235 Siddharth Chinoy Thu, 07 Aug 2008 21:43:50 +0000 http://www.micromouseonline.com/blog/2008/01/10/wheel-assemblies-for-decimus-2/#comment-235 What is the rated voltage for your motors? I have the 6 volt ones, and I'm afraid to use them at a higher voltage since they cost a bomb. Is it safe to exceed the said limit? I am also planning to use a 2 cell LiPo battery, but I was thinking of stepping down the voltage to 6V to drive the motors. It would save me quite some trouble if overvolting them by a volt or so doesnt harm the motors.(I'm quite sure it doesnt matter, but I'm being extra cautious just in case.) What is the rated voltage for your motors? I have the 6 volt ones, and I’m afraid to use them at a higher voltage since they cost a bomb. Is it safe to exceed the said limit? I am also planning to use a 2 cell LiPo battery, but I was thinking of stepping down the voltage to 6V to drive the motors. It would save me quite some trouble if overvolting them by a volt or so doesnt harm the motors.(I’m quite sure it doesnt matter, but I’m being extra cautious just in case.)

]]> By: peteh http://www.micromouseonline.com/blog/2008/01/10/wheel-assemblies-for-decimus-2/#comment-232 peteh Thu, 07 Aug 2008 17:27:52 +0000 http://www.micromouseonline.com/blog/2008/01/10/wheel-assemblies-for-decimus-2/#comment-232 You are quite right. The top speed referred to will be the most I can manage from the encoder resolution rather than what I can get from the batteries. However, the actual top speed is a little over 3m/s since I use a 2 cell LiPo battery. With a 3 cell pack it could reach the 5m/s. You are quite right. The top speed referred to will be the most I can manage from the encoder resolution rather than what I can get from the batteries. However, the actual top speed is a little over 3m/s since I use a 2 cell LiPo battery. With a 3 cell pack it could reach the 5m/s.

]]> By: Siddharth Chinoy http://www.micromouseonline.com/blog/2008/01/10/wheel-assemblies-for-decimus-2/#comment-231 Siddharth Chinoy Thu, 07 Aug 2008 15:15:13 +0000 http://www.micromouseonline.com/blog/2008/01/10/wheel-assemblies-for-decimus-2/#comment-231 You have stated that your reduction ratio is 4:1, wheel dia is 27 mm and that your top speed is about 5 m/s. But, the 2224 motors that you use have a no load rpm of 8000, which on reducing by a factor of 4, result in a 2000 rpm wheel speed. This results in a speed of approximately 2.8 m/s, which is inconsistent with the stated 5 m/s. Am I missing something? If possible, please show your calculations. You have stated that your reduction ratio is 4:1, wheel dia is 27 mm and that your top speed is about 5 m/s.
But, the 2224 motors that you use have a no load rpm of 8000, which on reducing by a factor of 4, result in a 2000 rpm wheel speed. This results in a speed of approximately 2.8 m/s, which is inconsistent with the stated 5 m/s.
Am I missing something?
If possible, please show your calculations.

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