Calculating Distance

General discussion of using Roboclaw motor controllers
User avatar
IMC Support
Posts: 824
Joined: Thu Feb 26, 2015 9:45 pm

Calculating Distance

Postby IMC Support » Sat Oct 17, 2015 12:10 pm

This a post to describe how to calculate the distance of a movement for the SpeedAccelDistance commands.

The simple distance formula is d = V*V/2a. This assumes starting or ending with a velocity of 0.

First you need to calculate the distance needed to accelerate to you speed and then to deccelerate back to 0. We'll call those d1 and d2.

If d1+d2 is less than or equal to the distance you want to travel then subtract d2 from the distance you want to move(will call that D) and use that for the first SpeedAccelDistance command distance. Then send a second SpeedAccelDistance command to deccelerate to 0 speed. The distance it takes to decel to 0 will be equal to d2 as calculated.

If d1+d2 is greater than the distance you want to travel you have to calculate things differently. You need to recalculate d1 and d2 using the ratio of the distances first calculated with the distance you want to move. The formulas are simple enough.

//Here is some psuedo code
//D, speed, accel and deccel are defined by you
float d1 = (speed*speed)/(2*accel)
float d2 = (speed*speed)/(2*deccel)
uint32_t dT = d1+d2
if(dT>D) {
d1 = d1/dT * D;
d2 = d2/dT * D;
d1 = D-d2;

SpeedAccelDistanceM1(0x80, accel, speed, d1, 0);
SpeedAccelDistanceM1(0x80, deccel, speed, d2, 0);

Return to “General Discussion”

Who is online

Users browsing this forum: No registered users and 3 guests