I hinted at another project i had in the works in my 81 ATC200 build post.... Well here it is! I have all the initial parts together, parts designed, prototypes made, and its come together enough for a sneak preview!
My 200ES has a speedometer which is nice because we city ride them here, but we are required to stay under the posted speed limit. The speedometer has gotten me out of a few arguments already when someone accused me of "tearing across town" and i showed the cops the speedometer which they didn't expect me to have. So for my 81 ATC200 i wanted to do the same thing but finding an affordable Hondaline Speedo is not an easy task these days. So i went searching for other possibilities. I did look at cable drive options, ones that used inductive sensors, you name it i looked into it. Then someone told me about a GPS speedo they have on their boat, although that one is calibrated in knots instead of MPH. However these GPS units are available in MPH also!
Cost was $53 shipped to my door, thats pretty cheap honestly. The body is plastic, the face is a metal ring and polycarbonate lens, not glass unfortunately but for the cost i wasn't really expecting glass. It has the most basic of connections, Ground, 9-32v DC for the Speedo, and 9-32v DC for the backlight, so just three wires. The GPS antenna is a separate unit that connects with small coax and SMA connector. I tried to find a speedo unit with a built in antenna but the choices were rather limited, and i suppose that makes sense as generally its going to be in a dash not in the open like it will be mounted on my 200 so a remote antenna is required.
I started by taking the original Honda speedo bracket and drawing it up in Fusion360 and then laser cut a wood prototype to compare to my OEM bracket, then i modified the dimensions to fit the GPS unit. It was actually not that far off on the hole spacing, the GPS unit is 70mm center to center on the mounting studs, the OEM Honda is narrower. So i just moved out the outward hole a bit, added another hole for the SMA connector to peek through the bracket, and then cut another prototype.
The end result was a perfect fit! Now as for the bushings, i did find bushings available from McMaster that would work for the GPS speedo and the stock bracket hole size of 1/2", but i didn't want to order 50 of them to get a couple. So i designed and 3d printed the bushings in TPU, TPU is a thermoplastic polyurethane, which is the material bushings and bumpers are made out of. I have had good luck with this material making grommets and bushings for other projects, headlight bushings, plugs, etc. So i made up a set for this. I did make them as two pieces though so they were easier to print and install in the bracket. Then i took some 6061 aluminum rod to the lathe and turned it down to 1/4" OD and drilled a through hole of 4mm to pass through the studs from the GPS speedo, the end result is an OEM style isolated mount.
I just got done designing a cup that will go around the speedometer, as well as cover and hide the wires exiting the back of the unit. Its currently printing, so once thats done hopefully later today or tomorrow i can get that all put together and get some more pictures of the design. The cup is going to be sanded and painted black to look like the normal metal can of a speedometer. It will all make more sense when its done and i get some pictures!
The mounting bracket design has been sent off for cutting in metal, i should have that next week i hope. I went with 6061 1/8" thick aluminum. I know the originals were steel, but this speedo is very light... Like less then a pound light, and even with the cup i am making to go around it the weight will not be such that the bracket will be stressed in any way, plus there won't be a speedo cable hanging down to the front wheel, etc. There just wasn't any reason to go super heavy on the bracket. The cost vs steel wasn't much different, but my plan was by going aluminum that i can anodize it black if i want, no painting, no rust, etc.
Anyway, that's where this project is for now, more updates as they become available. I also have a small rectifier/regulator that i am testing with the ATC200's AC output to give me the power i need for the speedo. The speedo is very forgiving, rated for 9-32v input, i tested it on my bench supply it gets a GPS lock in seconds after its first initial cold start, and works great across the entire voltage range. So that info will be shown when i get that done as well. The GPS antenna is going to go up in the headlight bucket, it will just get bundled with the DC wiring and get stashed in there. The plastic bucket won't cause an issue with the GPS signal. But the coax is long enough you could put it anywhere on the ATC front to back no problem. Just needs a clear view of the sky.