Hi,

I have had a DSI Pro ccd camera for some time, but haven't had the time to try it out until this weekend. I was taking some unguided images of Jupiter with my C8 and decided to try building a RA axis autoguider for the C8. I had a spare Meade 492 motor and it only took a couple of hours to fabricate a simple system that sits inside the forks and rotates the RA adjustment knob. Below are a couple of photos of the prototype. This sytem seems to work pretty well. The Autostar motor can rotate the RA adjustment knob and move the telescope. There is a fair bit of backlash in this adjustment knob and this system wouldn't work for full goto operation, but for autoguiding it may be OK. A rough test with a guiding program and my webcam shows that the autoguider will drive the Autostar system. I need to adjust the friction wheel that contacts the C8 RA knob and will probably add a small belt or rubber strap for better contact and to reduce torque on the worm wheel axis. Otherwise the prototype works very well for only a 3 hour project, and was a pretty simple and quick way to add autoguiding (RA axis only) to an older SCT.

Bill

Hi,

I had to modify the original autoguider design to remove the little friction wheel that turned the RA adjustment knob. Unfortunately the friction wheel required a small amount of pressure to give a good contact and this negatively affected the Autostar motor, giving drive and unbalanced load error messages. I replaced the friction wheel with a small cup, that fits directly over the RA adjustment knob. I filled the cup with hot glue and molded it to the RA knob. It easily pops down over the RA knob and grips very well. The entire assembly is mounted on a nylon kitchen cutting board and just slips inside the forks. The cutting board can slide parallel to the declination axis within the forks, and the motor can slide perpendicular to the forks; it sits within two aluminum rails and is held to the cutting board with strong elastic cord. The sliding motor assembly allows alignment of the worm wheel axis with the C8 RA adjustment knob axis. The autoguider system just slips into place inside the forks and is easily removed, keeping the C8 in an original-unmodified condition. I plan to construct a similar autoguider to turn the Dec axis fine adjustment knob (another rainy day project). Below is a photo of the final system and I will ASAP update my webpages with complete construction details.

Bill

Hi,

I finally had a few hours to finish this project and added a declination axis autoguider. I had hoped to directly couple the Autostar axis to the C8 declination fine adjustment knob, but this would mean having a motor portruding out of the fork. I decided to mount the motor on the side of the fork and use a small belt drive to turn the adjustment knob. Below are a couple of photos of the final autoguider. The top photo shows how I modified the Autostar worm wheel mount to accept a belt drive. The bottom photo shows the declination axis autoguider mounted on the C8 fork. The assembly is mounted to a piece of nylon cutting board that slips inside the fork and is held in place by a strong elastic band. I hope to get all the construction details posted on my website in the comming days.

 Bill

After what seems like 3 months of overcast weather, there was finally a clear night. I tested the C8 autoguider and it was able to move the C8 in both axis. The dec. axis motor worked perfectly. The RA axis motor also functioned OK and rotated the C8 in RA. Unfortunately the RA axis gear reduction was too large and the Autostar motor couldn't rotate the C8 fast enough to track! It was just a little bit too slow.

Since I used the Autostar worm gear assembly in the RA axis autoguider, this gave a 60:1 reduction. The C8 RA adjustment knob also has a gear reduction from the large C8 spur gear. So together these two gear reductions combined to a total gear reduction that was just too large for the Autostar motor.

I have just finished RA axis prototype nr. 3 and will test it tonight. This prototype uses a belt drive and is pretty similar to the dec axis autoguider. I am not too wild about belt drives on telescopes, but since an autoguider is a feed back control system, it should be OK. I would prefer to link the Autostar to the C8 without a belt, but its proving difficult to orientate the motor inside the forks without getting in the way of the OTA. It looks like I need to settle for a fork mounted RA motor and link it to the RA adjustment knob via a belt. I will post the next functional testing results ASAP.

Bill

Had a clear but very very cold evening this last weekend, and I had a chance to test the latest autoguider prototype. A first test in my workshop was successful, however an actual outdoors test gave problems. It was about -2 deg. F when I tested the autoguider. The elastomer materials (pully and belt) didn't react too well to -2 F; they became glassy and the pully couldn't grip onto the belt. Since the autoguider works OK in my workshop (at room temperature) it appears the problem is with the elastomer materials and not the overall design. Since warmer weather should be around the corner, I will retest this design as soon as the temperature rises a bit. I will have to search for an alternative elastomer material and replace a few parts in the fall. I may try to find a small sprocket and chain, eliminating slippage problems. In any event, the basic design seems to function OK and I just need to find a few alternative materials.

Bill