Jump to content

sgl_imaging_challenge_2021_annual.thumb.jpg.3fc34f695a81b16210333189a3162ac7.jpg

HEQ5 - Experiments with belt drive


Recommended Posts

Following on from this thread http://stargazerslounge.com/diy-astronomer/159157-eq6-belt-drive-modification-2.html the two sets of pulleys and belts arrived from Motionco.

First thoughts was how the heck will I fit them in the mount ! - The large pulley's like the ones in Georges thread are 15mm thick. However as it looks like I need to fit them inverted, I'm not intending to have the 3mm milled off their face to start with. I'll get them bored out to fit the shafts, then do a dry fit to check alignment of the belts and then see if I can reduce the thickness. My main concern is that the pulleys stick out too far that it becomes impractical to fabricate a cover.

It's going to be a few days before I can take parts to a local precision machine shop to get them bored out, and I'll post up a few pictures as I go...

Link to post
Share on other sites
  • Replies 115
  • Created
  • Last Reply

Top Posters In This Topic

LOL - I've only just removed the motors from the mount and you're suggesting I put together a kit - but I like your thinking :)

First stumbling block.. It appears unlike the EQ6, the small gear on the motor is push fitted on the shaft rather than attached via a grub screw. This means that if this can not be removed without damage (bear in mind I want the option to re-fit the gears if the mod doesn't work) then the modification ends here. If the mod proves successful and kits are made, it would be down to the user to cut the brass cog off the shaft.

I'll know more later when I take the parts to the chap that machined my pier adapter. I'll also ask the question how much he will charge to bore out and machine batches of these pulleys, and use that as a basis of costing out the kits.

post-23388-133877681481_thumb.jpg

Link to post
Share on other sites

Thanks for the suggestion, and it may be one my machinist may use. He seems to think it was bonded using a superglue type agent - anyway, hopefully I'll find out later. I'm sure it can be removed safely

Link to post
Share on other sites
good luck mate! I always thought th heq5 and eq6 used the same stepper motors?

Matt

Matt, I thought the same... mind you, I purchased this mount second hand, and I beleive it wasn't too old, but it may be that Synta have changed their design in recent months ?? It may be the same motors, but the cogs may be different

Link to post
Share on other sites

OK... had the parts bored out and skimmed, and spent the past couple of hours fuffing about trying to make this work. Here are my observations:

1) - to get the 5:1 ratio the 12t pulley has very little meat left when bored out to 5mm.

2) - like George, one of my pulleys seem to be bored slightly off centre so wobbles a small amount - the other is nice and true

3) - even having 4mm milled off the face of the large pulleys the grub screw is very close to the top of the RA and DEC shafts. Result of this is that they pop off the shaft quite easily. This could be resolved by drilling and tapping a second hole for a second grub screw (maybe this is why Synta use two on the gearing ?) or drilling and pinning throgh the pulley and shaft.. but that is something I'm not prepared to do

4) - Due to stock belts you have to file out the slots in the motor mounts to get enough movement to get tension on the belts. There is more tolerances for this in the DEC axis for this than the RA. However this results in the stepper motor encroaching on the view through the polar scope

5) - The stock belts increment in 10t. Whilst the 90t can be tensioned fine (other than the point mentioned in item 4) the 80t results in a very tight fit, putting a lot of tension on the belt and the shaft, more than I'm happy with.

6) being ali, it's very easy to knacker the grub screw trying to overcome point 1 - as has happened

7) the mount is nice and quiet when it did run with the ramp up/down of the motors hardly noticeable.

Whats really needed is a 3mm or 4mm belt, with increments of 2t so that tension can be easily maintained, and this would allow the pulley to sit further down the shaft and overcome points 1 and 6 It should also allow the cover to be re-fitted without any need for a gasket type spacer.

Cost - as a one off the machining cost me £40 (ouch). If done in batches it would be less.

Right, I'm off to try and put my mount back together.... unless I can find an alternative supplier for the parts more suited to this modification

Link to post
Share on other sites

regarding 3) couldn't you drill and tap a hole for a grub screw between the teeth of the pulley? With the belt going about half way round the pulley, there should always be enough grip on the belt, even with a small hole between 2 of the teeth.

Edit: This will obviously not work with the 12T pulley but might be a solution for the bigger ones.

Edited by yesyes
Link to post
Share on other sites

thats one possible option. I also noticed that the grub screws on the SW gear are larger than the ones used on the pulleys... I'm going to revert the mount back to stock gearing for now as tomorrow is reported to be clear, and will try and source some alternative belts. I'll also look at getting a tap and die set with sime meater grub screws... If I can I'll also pop the pulleys back to have a few more mm taken off if I can find alternative belts of the same pitch - the 12T pulley is fine - as it's quite deep on the shaft

Link to post
Share on other sites

For the EQ6 conversion its better to skim whats needed off the tooth end of the pulley as the hub gives a perfect spacing for the cutout in the casting, this means Ive not had the problems with grub screws you have.

GOTOS have become slightly better which means Chris's alternative ratio code for EQmod is spot on, tracking is also spot on with PHD, unfortunately you need around 40 minutes of data to get a meaningful PEMPRO graph......hopefully soon :)

Link to post
Share on other sites

George, I had the guy machine around 4mm off the tooth side of the face, which left enough meat on the pulley for the thickness of the belt. The problem is that unlike the EQ6, on the HEQ5 the pulley is in effect mounted inverted on the end of the axis shaft, leaving the grub screw little to grip onto. Having more metal machined off would allow the grub screw to sit lower down the shaft, but then the belt would overlap the pulley

I'm searching for alternatives that either have additional grubscrews or look at yesyes suggestion of drilling and tapping through the teeth of the pulley, but don't really want to risk affecting the mesh between pulley and belt. However, having spent around £70 on this so far, and have mechanical issues (wobbles) with both a 12t and 60t pulley as the guy obviously didn't use a lathe, I'm on a limited budget as I don't want to waste any more cash. I'm also looking at a complete drop in replacement where the pulleys are supplied ready bored to suit the shafts, and the belts are the exact length (have to be custom made).

If Chris is looking in, can you elaborate on why 4:1 is not a good ratio for the HEQ5 or why 5:1 is preferable. Some of the pulley systems I've been looking at results in a 60t too large to fit within the casing when used with a 12t motor pulley.

Edited by malc-c
Link to post
Share on other sites
If Chris is looking in, can you elaborate on why 4:1 is not a good ratio for the HEQ5 or why 5:1 is preferable. Some of the pulley systems I've been looking at results in a 60t too large to fit within the casing when used with a 12t motor pulley.

The mount itself is designed with one overriding purpose - to track at sidereal rate. The firmware is therefore optimised to run the motors at sideral rate using the original gearing ratios. If we change the gearing ratios too radically there is a danger that the firmware design is no longer optimally matched to the rate at which is must now update the steppers to maintain sidereal.

There are a couple of other factors that changing the ratio will affect.

1. Resolution:

With the standard gearing each microstep of the stepper results in a 0.144 arcsec of angular movment. With a 5:1 ratio you loose a little resolution and this reduces to 0.15 arcsecs, using a 4:1 ratio gives 0.1875 arcsecs and a 6:1 ratio gives 0.125 arcsecs.

2. Slewing speeds

When the mount performs a goto it moves at the fastest rate it can. If we change the gearing then clearly we affect slew rate. Using a 4:1 ratio will result in faster slews (about 25% faster).

Now it may be that the 4:1 or 6:1 ratios will work just fine and I guess we won't know unless some one has a go. There is one guy who took the EQ6Pro up to a 7:1 ratio and he seems happy enough (although his gotos are slow!). My comment about the 5:1 ratio being preferable was really just to guide you down what I considered to be the safest option.

Chris.

Link to post
Share on other sites

Malc in this thread there was some pre-discussion on pulley suppliers etc, HPC Gears Home page offer a service to customize their range of gears ie a re-boring service etc, if I find the slight runout on my stepper pulleys is effecting the mounts PE I'll probably get replacements from them prebored to 5mm.

Ideally Im still looking for a 12 tooth steel rather than the more common alloy offerings, not had any luck finding a supplier yet. Custom made would probably be too expensive for one offs but may be worth inquiring about.

Edited by George
Link to post
Share on other sites

Thanks guys for the additional feedback. I agree 1:5 is close to the 1.44 arc settings. I guess that if these were too high that the scope would either lag behind or overtake the target when tracking ?

I'm still searching for suppliers who offer plain pulleys and a boring service, and custom length belts. I too found issues with the run out and facing, even though I stressed how important it was to get them true. I looked at HPC, which originally seemed expensive for the parts and re-bore. That was before I got flushed £40 from the local machinist.

Link to post
Share on other sites
That was before I got flushed £40 from the local machinist.

Daylight robbery for little more than 30 minutes work :)

Think HPC is your best bet, Im actually looking for a decent mini lathe for some additional projects I have in mind :(

Link to post
Share on other sites
Daylight robbery for little more than 30 minutes work :)

Think HPC is your best bet, Im actually looking for a decent mini lathe for some additional projects I have in mind :(

Must admit it was a shock...

It would be nice having a decent workshop or lathe that was up to turning and facing to do these odd jobs.. just don't have the space (or funds)

Link to post
Share on other sites

My Dad had a small lathe and I turned a few small items many many years ago. Must admit, I'd like a small lathe to turn that sort of small thing. It would have been great for making the parts of my home made weather station. Trying to file things round and making holes central and straight is very difficult by hand! :) Funds are my problem (as can be seen by my obsy build thread where I've had to wait for available funds to buy the bits).

Link to post
Share on other sites
Just googled the mini-lathe... £400 Ouch !!

I don't think I would use it enough to warrant that investment, even if I had the cash !

Yes, I came to that conclusion! That would go a long way towards my next scope!! :)
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.