Chief Delphi - Reducing the speed of motors

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Rangel

27-01-2011 18:37

Reducing the speed of motors

Hello, my team has just got one of our robot chassis built. I then ran tank drive code on the robot and one thing we noticed is that it drove fast. Real Real fast. So what we want to do is cut the speed of the robot in half. How would you give less signal to the pwms.

Vikesrock

27-01-2011 18:45

Re: Reducing the speed of motors

If you just want to cut the whole range in half, simply multiply the joystick inputs by .5 before passing them to whichever drive VI you are using.

Mark McLeod

27-01-2011 18:51

Re: Reducing the speed of motors

Increase the size of your wheel sprockets...

Ether

27-01-2011 19:19

Re: Reducing the speed of motors

Quote:

Originally Posted by Rangel(kf7fdb) (Post 1009960)

What you really should do is change the overall gear ratio on your robot so that when you are commanding full voltage to the motors, you get the vehicle top speed you want.

You can do this by increasing the size of the wheel sprockets (as Mark suggested - if you are using drive chains), or by using smaller diameter wheels, or by using a Toughbox gearbox (12.75:1 gearing) instead of the CIMpleBox (4.67:1 gearing) supplied in the KoP.

If you reduce the speed by simply scaling down your joystick outputs in software, you'll wind up with a robot with low acceleration and without much pushing force.

Rangel

27-01-2011 19:22

Re: Reducing the speed of motors

Quote:

Originally Posted by Vikesrock (Post 1009962)

If you just want to cut the whole range in half, simply multiply the joystick inputs by .5 before passing them to whichever drive VI you are using.

Thanks. I guess I forgot to mention that we wanted to go that fast but not all the time. Now we can choose how fast to go.:D

PAR_WIG1350

27-01-2011 22:41

Re: Reducing the speed of motors

Quote:

Originally Posted by nckureghian14 (Post 1009989)

reducing the voltage?

No, that would mean less power. Technically, this never happens anyway, but i don't think we need to get into that.

Quote:

Originally Posted by Mark McLeod (Post 1009965)

Increase the size of your wheel sprockets...

Yes, this allows you to leave the code alone and still get full power. To cut the speed in half (approximately), the wheel sprockets should be about twice the size. As a bonus, you also get more torque.

EDIT:

Quote:

Originally Posted by Rangel(kf7fdb) (Post 1009983)

Thanks. I guess I forgot to mention that we wanted to go that fast but not all the time. Now we can choose how fast to go.:D

OOPS, I missed that. In that case, forget what I said.

Vikesrock

27-01-2011 23:01

Re: Reducing the speed of motors

Quote:

Originally Posted by Rangel(kf7fdb) (Post 1009983)

Thanks. I guess I forgot to mention that we wanted to go that fast but not all the time. Now we can choose how fast to go.:D

Ok, so what it sounds like you want to do is use a mapping function to give you more control on the low end with the same maximum signal. This thread talks about various mapping functions, x^3 or variants of it is a common choice.

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