Portable Dynomometer

[salt-racer]

Portable Dyno Update:

I finally figured out how to post a photo and establish an album (thanks John) Hooray!
I had originally attached a message to explain the photo but who knows where it went...another story of it's own.
Anyhow, this is where we're at with the dyno. I had to redesign the hydraulic drive system as the original cog belt drive proved to be inadequate and skipped teeth with any significant load.
I decided a roller chain set-up was the next logical route and proceeded to gather the necessary parts (thanks to E-Bay).
Onward to a quality # 40 pre-stretched roller chain, sprocket and some machining.
Now comes the Big test! Although I designed this dyno primarily for my little Yamaha 100cc Land Speed Racer (LSR), I also wanted it to be capable of handling my friend Steve's (Bonneville teammate) '99 Honda 250 hawk (turbo) who will also share my pit at the salt flats next August.
This is where John H. and his Honda 250R comes in. We strapped it to the dyno and ran it to see how well (or not) it worked out with the new chain drive (remembering that the Kawi KE 100 skipped teeth on the old drive when we loaded it down). We fired and warmed-up the 250R and proceeded to apply load until the valve was fully closed and all the pressure was being diverted through the relief vale at 2,800 psi, wow, John's Honda had brought the dyno to it's knees...
Back to the drawing board, again...
Oh, btw the knobby rear tire tracked real nice on the 5.00-5" aircraft tire even at speed w/o slippage, great news!
After further thought and shop discussion, John and I realized the dyno needed greater load capacity and the easiest way was to increase the hydraulic flow (pump rpm). The Vickers vane pump is rated for maximum flow at 3,000 rpm and I was currently running it close to 1,500 rpm at 100mph wheel speed. Sooooo, now I have ordered a larger drive sprocket. I will step-up to a 25 tooth and remove the current 16 tooth.
To be continued.....
George, Tri-mac Speedsters race team

[salt-racer]

OK, I promised an update...
I removed the 16T sprocket and installed the larger 25T sprocket in it's place on the drive wheel axle. The object was to increase the load capability of the dyno by increasing the pump rpm's (flow, gpm). The new ratio is 0.83:1 whereas the old was 0.53:1 and results are GOOD!
I can now run John's XR250R at WOT in 6th gear on the Dyno (still can't load it to 'stall' but very close). I figure when I run my teammates Honda 250 at Bonneville with tall LSR gearing (100mph), that it will create additional load and be sufficient for his tubo'd 250 cc (@ altitude 4,400 ft.) and still be in test-range for my 100cc Yamaha.
Post Dyno run, John and I were talkin' about how nice it would be to know the surface speed or mph that the drive wheel was spinning. I did a little digging and found several digital bicycle speedometers, most are wireless with a little magnet attached to the spokes and a transmitter to the fork leg and they are rated at up to 99.9 mph. This may be an adaptable speed system for the dyno. I was wondering if anyone in the group has had any experience with these speedometers or may know of some other alternatives/suggestions....??
Speedless in Blyn,
George

[salt-racer]

Hello guys

http://www.denbrook.com/Motorcycles/BC800/index.htm

The last entry on the dyno I had asked if anyone had any experience with the small bicycle speedometers as I was contemplating installing one on the portable dyno for actual speed indication (how fast will this puppy go?). Tom saw my request and happen to have a couple of the old bicycle units laying around and offered them to me to try out. One of the units was a Sigma Sport #BC800. It is the same speedo that was used in the above article I found while searching out info. Seems I'm not the only one wanting to install on of these tiny speedos on a motorcycle application. The above link on the internet shows one being installed on a sport bike. This is just one of several articles I stumbled onto.
Last night, as a test, I decided to install it to the rear wheel of my LSR Yamaha on the table. I lengthened the wires (necessary for a motorcycle install) and using a small fractured piece of rare-earth magnet (from and old hard drive) taped to the to outer rim, I started and ran it up to speed on the stand..... and the readout quickly indicated 85mph.... perfect!
Next step is to install on the small 13" diameter drive wheel on the dyno and see if works on it!
Later guys
George