Close

8.2 mile drive

A project log for Ultimate running aid

Eliminate everything from running but the running part.

lion-mclionheadlion mclionhead 02/22/2018 at 03:220 Comments

The HKS-9257 arrived after 2 days & was the wrong size, so into the pile it went.  Such is the peril of modern, sight unseen mail ordering.  

The latest theory was an accidental observation that none of the servos can automatically recover if they're knocked out of position by a momentary force.  They usually get off by a certain amount & stall as they try to recenter, even if the force has ended.  The servo saver improved results by always exerting less torque on the servo than the servo exerted on it, so the servo didn't get knocked off center & the servo saver still had that center position to exert on the wheels, after a delay.  

The Futaba S3003 was particularly bad at centering itself, so replaced it with the only remaneing servo, an 18 year old Hitec S311, the very 1st servo bought by a lion.  It was slightly better at centering itself.  It didn't fit any servo saver, so choked up on the servo horn to increase the force.

The 8.2 mile drive with no payload besides the speaker & no headlights sucked 2956mAh or 360mAh/mile.  The servo itself might be a significant draw, since the LM317 gets hot & it buzzes when driven at 150Hz.  150Hz was a requirement to reduce oscillation.  P=200 D=0  & it had acceptable levels of oscillation, but wasn't totally solid.

A brief test with the polecam was most impressive.  P=100 D=100 with the bandwidth=0.9 managed to stabilize it more than any previous drive.  Things started looking up for the FIR filter, with the servo change.

Rather than invest any more in servos or algorithms, the decision was made to finally scrap the lunchbox after 3 years & many hundreds of miles.  Should put on the new tires & wear them out.  Lowering it by eliminating the suspension caused problems with steering which will probably never be completely solved & there are other vehicles which can do the job without any modifications. 

A novel way to fix a stripped hex head.  The light duty cutting wheel does the job.

Original servo saver.

Shorter servo head.

Discussions