[Second Series]

I messed around with trying to reverse engineer the DRAC for many hours. I have some components to play with, but many more hours will be required for that project.

I rebuilt an old speedometer that I had. It might be a 1948. I don’t know what I did with the original ’47 speedometer that came with my panel truck, it was missing the needle. I had been using a newer speedometer from what I don’t know. The newer one had ’63 written in pencil on the inside. I got a refacing kit for the ’48 speedo and lubed everything. After that I noticed the high beam indicator lens was busted, so I found a refresh kit. I reassembled and then discovered the spindle had become independent from the speedcup. I glued that, but don’t know the correct orientation. The speedcup was binding so removed the glue and shimmed the speedcup and reglued, still not knowing the correct orientation.The speedcup still was binding, I loosened the screws for the speedcup assembly, and the needle bracket and was able to shift it enough to get free movement of the speedcup, and then tighten the screws. The orientation of the spindle to speedcup was off, the needle didn’t bottom out at zero. I tried to rotate the speedcup past the stop, but then the speedometer wouldn’t overcome the spring tension. While trying different things, the stop broke off. I let the spring at rest, preloaded the spring about 20 degrees, and glued a wire as a stop. The needle had a visible fracture, but was o.k. It broke during final assembly. I didn’t want to wait another week for a new needle, so I glued it. Now the speedometer that I plan on using is working smooth and quiet.

I had made a new bracket for the motor, so now I can finally try it. The motor connection has to be precise so it doesn’t bind or change. That could throw off the code and change operation of the needle. The new bracket threads onto the speedometer. Like the first bracket it uses standoffs to mate to the motor. I’m using a drill press, and it just is not precise. I had been wanting to use grommets somehow for both as sound damper from the motor, and to add some wiggle room to prevent binding. This is not ideal, but I located some small grommets and overdrilled the motor bracket holes. Untimately it would be good to have the bracket assembly machined to spec, but at this point this one off works.

I struggled with getting a good curve equation for this speedometer. I wasn’t doing something right, or the speedometer was just too funky to work, or maybe both. I finally found that I could remove the outer data points to get the torque curve, and then use the full range for the smooting curve to compensate for that. So now this speedometer reads acurately between 20mph and 74mph. The top speed is 80, so I can fix the top end in the code. The low end will use the optical disk, so I’ll dial that in too. The motor starts to turm the speedometer at about 4mph though so I could probably get away with not using an optical disk. The freshly lubricated speedometer makes a huge difference.I was working on some code that compares the optical disk speed and the input frequency, so I’ll implement that too. Later on I’ll research PID, but for now it should be good.

The arduino and motor control board, I’ll modify the motor control board so it powers the arduino and mount them both in a box. I’m currently powering the arduino via usb.

I’m still planning on connecting this to my 1990 k2500 and comparing the stock speedometer with mechanical speedo side by side. But as of now I can state that you can slap a motor on the back of your mechanical speedometer and connect to a modern transmission.