ATRIAS 2.1 Handbook/General Information/Cost of Transport Definition

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At some point the info below should be distilled down to useful info and presented in a wikipedia/textbook/encyclopedia format. This email chain was provided to me [Jesse Grimes] by Jonathan Hurst concerning cost of transport


I misspoke on the phone. If you are at 0.5 A and 50 V, then you are using 25 Watts. Let's say you are moving at 1 m/s and the ATRIAS Monopod weighs in at 20 Kg.

THEN....and you will like this.............

Mechanical Efficiency = 25*1/(g m distance) = 25 / (10*20*1) = 25/200 = 1/8 = 0.125

The number for a human walking is 0.05......and ATRIAS is hopping. Your robot may be a game changer!

Here are the numbers given by my simulation, with torso stabilization:

Step 50 completed at time t = 18.7972, Stride duration = 0.37769, Speed = 1.588, Stride length = 0.59976, cmt=1.028, cet=0.12047

ATRIAS is much closer to the net power, which allows negative power to be shunted to the battery, than to the efficiency estimate that looks at positive work and gives no credit for negative work.



I was confused about the difference between CMT and CET. The paper by Ruina, cited by Koushil below (see link) clarifies this. In my simulations, I had been focusing on CMT because that is all we can estimate for MABEL. For ATRIAS, it is easier to do the CET, from what I understand.


Dear Prof. Grizzle,

Sorry, missed your mail. Prof. Geyer is specifically talking about CET, the specific cost of energetic transport. We have never measured this value for MABEL. We calculate only CMT, the specific cost of mechanical transport.

This paper [pdf] (refer pg. 2, column 2) mentions human CET = 0.2, and human CMT = 0.05.

MABEL min CMT = 0.1, and we are a factor of two away from that of humans in this regard.

Thank you,


NOTE: Said .PDF file was not attached to my email. -Jesse Grimes


Here is some COT data on humans and horses for different gaits.

For the human data, assuming a body weight of 70 kg gives a walking minimum of COT = 2, or if divided by gravity, CET = 0.2. For running that will be about twice as much.

For the horse data, the weight is about 140 kg, and 1ml_O2=20J, yielding the same values for minimum walking COT and CET as those for humans. However, horses reach the same minima in other gaits at higher speeds as well.


File:COT horses.jpg
Cost of transport of horses at various speeds and gaits
File:COT human.jpg
Cost of transport of humans compared to other various locomoting things