Tinkering with the Servos, a New Catch and More Sensors          

M53660L

I converted the Power 1501MG servos to have their positions digitally read and then sent speed PWM signals to them instead of position signals. This method works much better for fast moves and now the servos do not accidentally loose their positions. But another quirk of the 1501MG’s internal logic seems to be that for slow speed moves, there is a built-in delay of up to two seconds!***  I am going to scrap the electronics inside these servos and replace them with standard M51660L servo controller chips (eBay $2.50).  

Ultrasonic distance sensor.

I installed an ultrasonic distance sensor (ebay $3.98) on the cart frame to monitor how high off the ground the legs have lifted the cart. It uses two Arduino digital channels, one to trigger the ultrasonic pulse and another to detect the echo.

Break switch.

I made a break-peddle activated switch to tell the Arduino that I’m pressing on the break.

Hall effect wheel speed sensor.

I made hall-effect wheel sensors to detect how fast the cart wheels are turning. It sends a positive pulse to the Arduino every time the cart moves forward eleven inches; that is ¼ of a turn of the cart’s wheel.

Caliper

I am redesigning the leg catch system. In addition to freezing the position of the leg at the hip when the leg is all the way back, I may want to lock the leg in the forward position as well. I made pneumatic calipers that ride on the front of each leg that can grab on to an aluminum bar and are able to stop the leg swings at any position. The calipers are cheaply made out of a 2” PVC fitting and a piece of rubber inner-tube. A couple of 24 volt pneumatic MAC valves from the junk box activate the calipers. Unfortunately, I have to do quite a bit of disassembly of what I’ve already built to make the change.




*** The 1501MG servos are good. See July 19, 2014 entry for explanation.