Monday, 25 June 2012

One step backwards, two steps back

Almost a week ago now we set about fabricating the main supports for the reverse.  All went pretty well, although we did decide that we should put something on the back too - so I need to sketch something and get it water cut so that it will bolt straight onto a chassis tab that I'm yet to make also.
Naturally its all just tacked at the moment... although that didn't stop me from connecting a battery and seeing if it worked...
I did even have a video but I managed to delete it by accident, clever lad that I am. Actually I've been a bit dull. 2/3 times the gear seems to work a treat - out it pops'n'spins turning the prop flange as planned.  However, 1/3 times the bloody gears don't mesh properly and you get a nasty chattering sound.  Why?  Well, neither gear has a chamfer to help it mesh.  DAMMIT!  The point is that no real harm is done at the moment but its only trying to turn a shaft in a high quality bearing.  It's going to have to move at least 515kgs.

So, what now?  Well, I thought things through enough when I 'designed' the system that I've had the expensive gear hardened so that the the cheaper one wears.  This was a great idea at the time.  Unfortunately convention would have me chamfer the smaller gear.  Ah, woe is me.  Time to adapt; either try to chamfer the big gear with the Dremmel or get a chamfer put on it by a machine shop and see what happens.  I've not decided what the right thing to do is yet.

In other news, last weekend's racing at Donington Park was originally planned to be my RGB debut - hilarious level of optimism obviously.  Not being able to drive a glorified climbing frame, I travelled up to watch yesterday instead.  Most folk seem to be going faster.  Al Boulton dominated Class F as normal while Tim Gray took another outright win by a country mile.    Perhaps the most important thing for me was the fact that Paul Rickers' 4C8 R1 is still going strong.  Good news!

Next time - a sexy water-jet cut dash mount.

Tuesday, 12 June 2012

500 pounds of ballast!

I got home this evening to find that the custom drive gear for my reverse mechanism had finally arrived.  About time too!

So, it was more-or-less straight out to the shed to see if everything would hang together as planned.  Ah yes, the plan.  The plan was originally to use an unmolested starter motor from a Honda Civic to engage on a cog mated to the propshaft-to-gearbox-output-shaft adaptor to drive the car in reverse; rather like a milk float.  A very slow milk float.

Now, while I can't really claim the original idea as my own, the system that I was essentially copying didn't quite meet my brief.  Dan's ( method engaged the starter with a button and a mechanical lever.  This sounded far too complex and involved more components than is, to my mind at least. strictly necessary.  The idea was therefore to have a purely electric system.  The problem was that the planned system would work brilliantly right up until the point that you realised that the electric motor would get in the way of the propshaft - a fairly critical component when looking to propel the car in either direction.

After much head scratching I decided that the only way forward (or backwards as it were) was to replace the driven gear on the starter motor - the 'slave' gear was already as large as I could get it.  I originally planned to fit a standard 2.5MOD gear of the correct PCD and O/D to the innards of the original gear - having had the original external teeth machined down.  We did get as far as machining the teeth off before I conceded that it was likely to be a horrible bodge - welding to hardened steel wasn't going to be terribly easy and the need for a fairly small centre bore meant that I couldn't get a HPC-supplied gear off the shelf anyway.  The picture below shows the original gear in its current state as well as a portion of the 'nose' of the starter which I cut-off to provide greater clearance for the new driven gear.
I obtained a quote from HPC Gears, having sent them a decidedly non-engineering drawing and the original part.  While it took a while to be delivered, apparently due to outsourced spark erosion, I can't fault the part itself.
This then gave me the kit of parts seen below.  
Inclusive of the machined bushes, both gears and reconditioned starter, this lot owes me about £500 i.e. about the same as MNR charged me for a reverse box a couple of years ago.  The upside is that the new electric kit is much lighter than a gearbox.  
The downside is that I'm not certain if it will work.  Due to a driven gear that is larger than those on most  BEC electric reverse systems, the torque required will be somewhat greater than on other solutions.  Hence, everything needs to be sturdy, including the electrics.  Of course all it needs to do is reverse the car on flat ground and hop a wheel over a bit of wood to pass scrutineering, but I'd be gutted if I'd got this far and the thing flunked the test.  Time will tell.
While this all seems like a terrible faff, the fact is that 'rules is rules' and if they, meaning the increasingly active eligibility scrutineers, find that your reverse mechanism doesn't do what it says on the tin, then you get disqualified.  This has already happened a couple of times this season.  Its possible to form a decent argument to say that these potentially-token reverse systems are a waste of time and money and just add weight to the cars, but the diktat comes from the MSA rather than the club so its not even a fight worth fighting it seems.

I need to get some supports fabricated and get it welded in next.  Adrian has done a good job of bracing his ancillary starter motor so I need to look hard to see if I can do something similar.


Sunday, 3 June 2012


As part of the effort to get the chassis itself finally completed and sent to be powdercoated, attention turned to the fuel tank.  I have no aspirations to make my own but the mounting points had to be set-out in such a way that the part, once fabricated, could bolt straight in with minimal fuss.  This meant fabricating a template that I could use to locate the mounting points while the tank maker could use it to help make the tank itself.

The plan for the tank is another good idea that I've stolen from someone else.  Matt and Ivan at Procomp Motorsport can be thanked for this.  Here's one they made earlier:
The idea is that the tank sits against the back bulkhead and above the axle on the passenger side.  While the mass of the fuel sits quite high, there are a number of advantages to this method:

  1. The tank is well away from the rear of the car and therefore less likely to be interfered with in the event that the car hits a tyre wall backwards.
  2. The weight is over the rear axle; Procomp's LA Golds have a habit of outrageously good starts and one suspects that this plays a part.
  3. The fuel and tank should, along with the engine which is also placed as far to the left as is possible  (from a RHD perspective,) go some way to balancing-out the weight of the driver i.e. me.
So, having made a couple of cardboard templates, I the dragged out the jigsaw, files, sanding block and drill and produced the following.

Its worth noting that mine is wider than the Procomp version.  I suspect that my bulkhead isn't quite as tall as on a Locost and I have the Brikett 6-hour relay in mind so want a little extra capacity.

The tank will eventually be mounted with the same style threaded inserts that we used on the engine mounts, as seen here.  The tank will be isolated from some vibration by using 5mm thick rubber washers.  The mounting method can be seen below.
Again with chassis completion firmly on my mind, I also wanted to decide where my Digidash 2 was going to live.  After much deliberation I decided that behind the wheel would be best.
I'll now probably get the mount water-jet cut so it can be tig-welded to the column.

That's it for now.  I'm still waiting for the reverse gear and motor to return, but I've been promised that I'll see it this week.  Fingers crossed!