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Re: Mechanical speedometer drive solution
My initial plan was to use an off the shelf solution, I found a couple available. In my search I also found discussions of building your own. I also discovered that I can replace the tail housing and use a mechanical speedometer cable, there are several signal sensors with pass through for mechanical cable available. It’s good to have options. I’m having fun playing with electronics.
I received the motor from Dayj1, Thanks again! It is a DC motor with optical disk, not a stepper. I found it is used in a Lexmark printer for paper feed. It does run at 2,136rpm for 128mph, but I couldn’t get it to run slower than 160rpm that works out to 9.6mph. I could gear it down, but 1.5:1 would get 6.4mph to 85mph. I like that it has the optical disk, I’ll play with that.
Part of the issue could be my test setup, I’m using a BJT transistor for the motor supply, a FET might be better. The PWM is 12v, I could try different frequencies, or voltages. I may fine tune it at some point, but it works for now.
Someone tore apart a broken vacuum at my work, I found the motor in the scrap bin. It’s from a Dyson cordless, unfortunately the shaft was bent. It kind of worked, I tried to unbend the shaft, and it has a good range, but too fast at 100rpm to 8,000rpm . The shaft is 2.3mm and I have some gears from the hobby shop for 2mm. I set it up with 5.5:1 gears and it’s good for 3mph to 100mph. It is a Johnson motor, but I was unable to cross reference the numbers on their website. I did locate a similar motor by looking at size and supply voltage. There is also the spec. of Stall Torque, that may be related to how slow it will run. I’ll order a few different motors to test. I’m still curious about using a stepper motor, so I’ll keep searching.
The code has some bugs and needs to be cleaned up, but it works for 2Hz and up. I’m ready to connect my speedometer to these motors to see how it effects the motors.
It looks simple enough to build a DRAC. I can use an op-amp as a Schmitt trigger to clean up the VSS signal and produce a nice square wave.
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