Saturday, 20 July 2013

Schumacher Mi1.5 build...

OR... how to take a really old car, fit it with parts from some not as old cars and hope you get something that works!

I really needed to find a car that I could run locally to keep my driving skills up. The first option was, of course, to buy the latest and greatest but I was quickly dissuaded from doing that by my minster for finance and warfare (my wonderful and long suffering partner). Next option was to buy a recent version 2nd hand car but this didn't prove much cheaper with a good Xray T4 or Schumacher Mi4 demanding around $400 for decent condition. Even an Mi3 or T3 will still hit the for sale threads at $250+. 3rd option was to buy one of the cheaper "sports" versions of a couple of cars E.g. the 3Racing Sakura XI Sport, but I wasn't convinced mainly because I'd be buying a car I didn't know and most of the sport level cars leave things like sway bars and threaded shocks in the options catalog. This adds to the cost if you try to race it seriously, which just means you end up spending less on the car but more on options.

This left me with the idea of refurbishing one of my older cars into something that I could use. I love my Tigermoth LCG, but this car is now completely out of production and parts are getting rare, and even some of the alternative parts I've manged to fit in place of original parts are getting harder to find. I didn't think there was much point dragging the old Tamiya TA03 out (and its buried in a box in storage anyway) so the only option left was my Schumacher Mission. Fortunately the Mission has, relatively recently, been reborn as Schumacher's sports level car, the Mi1. The Mi1 is based on the original Mission platform with some updates to accomodate LiPo batteries and a narrower chassis. However it retains the original single pulley lay-shaft and basic suspension architecture of the original chassis. As such, its quite an old design and compared to most modern cars would be considered outdated in areas such as chassis height and CG as well as being quite bulky in upper arm mounting. Also the diff bulk heads are not very convenient by modern standards, making repairs and maintenance slower and more tedious.

By chance I was looking through a couple of British RC forums and I happened across a guy who was looking for a way to prolong the life of his own Mission. This was before the Mi1 had been released and he was worried about things like belts etc being hard to get as the Mission doesn't share belts or many of its suspension parts with any other car. He had discovered that the Mi2 diff and center pulley would fit. Unfortunately this is as far as he got before the Mi1 was released but it started me wondering if drive line parts from later cars would fit. A bit of time on the Schumacher website and it became apparent that despite the huge differences in the newer Mi cars, a lot of parts remained the same. Diff pulleys and diff out drives are the same on all the cars right up to the current Mi5 as are internal parts like diff rings, thrust washers etc. This means that despite all the other changes, the width of the diff bulk heads has never changed. 

As luck would have it I was perusing the Australian RCTech For Sale thread and came across someone selling a complete SpecR Gear Diff for an Mi4. This was the moment I cast the die and committed to try to build my own "Mi1.5" as I later decided to call it. A quick phone call and my Mission was on its way from storage to me. It wasn't quite that simple but it would be tedious to try and write it all out and even more tedious to read. I also spotted a Lipo mounting kit for the Mi1 for sale so grabbed that as well. Plans were forming in my head so I jumped onto my favourite online hobby store, that stocks a lot of stuff I've just never seen locally, and placed an order for the bits I thought I would need.

Then I waited... and waited..... and......

It may be me but express international freight (I originally typed "fright" there which may be a Freudian slip) costs seem to have taken quite a jump in recent times. So I decided to save some money and have things sent to me regular post. In the time of the "now" generation, 7-10 days can feel like an eternity but I eventually had a couple of boxes of parts and a car to put them onto.

Center Pulley
The first job, and most important given the intent of this project, was to create a new center pulley. The original Mi1 belt lay out sees a single main belt driving the rear diff and then a long belt running from the rear diff pulley to the front diff. The Mi1.5 replaces this with a more traditional belt layout with the center pulley driving separate belts to both the front and rear diffs. The rear belt and pulleys are not difficult as the original Mi1 pulleys and belt will do the job just fine. However the Mi1 is designed to drive only one belt on the center shaft so a modification is required. The original forum showed the use of an Mi2 center pulley, but I wasn't sure I could source one of these plus I didn't want to spend money on something that may not work or be useable. My stock of Mission parts delivered up 2 original plastic 20T pulleys. It was quickly apparent how these could be modified.

Mission belt pulley showing factory molded holes, probably for weight reduction. This pulley has already had the ridge for the belt fence removed

Showing the rear of the 2nd pulley with 2 of the holes from the front drilled fully through.

3mm carbon rod epoxied in to form drive pins. If this isn't sufficient I have some 1/8" steel rod to try instead, but that will obviously increase weight significantly. This picture shows the pins in the rear belt pulley but they ended up being fitted to the pulley for the front belt. This works better for installation.

Everything fitted together - space is at a premium and I do have some concerns that the pulley doesn't grip the drive pin in the shaft by enough to be reliable long term or for more powerful motors. My intent is to run 17.5 or 21.5 so hopefully this design is sufficient.

Rear Diff
The next step for me was to build the new hear diff. This was something totally new for me as I've never built any other gear diff except for the Tamiya gear diffs and they are hardly comparable. Fortunately, the SpecR range of gear diffs are quite popular so there is a wealth of information on the net regarding the best way to build and set one up. I followed the SpecR and Schumacher guide for building it with only one diversion and that being on the oil I filled it with. I chose to go for a heavier oil as, according to my research, many people recommended a heavier oil if coming from only using ball diffs to a gear diff for the first time as it provides a more comparable feel.

The SpecR gear diff fresh from the packet. I had a minor scare when I thought I was missing some shims but turned out to be a case of things stuck together. Duh!
Completed diff fitted perfectly into the original bulkheads. Original belt fits as well though the one in the pic is a temporary one. I am not yet convinced on the plastic out-drive cup things but proof is in the using.

Front Diff
At this end I decided to take a leaf from the LCG and make a Slipper spool. The advantage I've seen from the slipper spool is that under "normal" circumstances it functions perfectly well as a spool but in impacts or extreme circumstances it can slips and this can take pressure out of the drive-line rather than transmitting it along until it finds the weakest point. I've never broken a drive shaft or out drive in all the time I used the LCG so I am hoping for a similar result with the Mi1.5, especially as for the time being I will retain the composite drive shafts (sorry Schumacher, I can't justify $44 for a pair of drive shafts at this point). I had spotted some option pad things Tamiya supply to go in the diff's of their drift cars when I was looking for new parts to replace the ones in the LCG but I'd never had the chance to order them until now.

Tamiya friction pads and Mission front diff pulley. The pulley had to be drilled out to take the pads as it uses 2.5mm diff balls and Tamiya use 3mm. Originally I intended to use this standard narrow pulley but for reasons explained later I switched to the wider rear pulley for the time being.
Front Belt
This is where the Mi1.5 build got a bit interesting. Everything up to this point had been simply modifying existing parts. I already knew that the Mi2 belt would not fit as it was described in the original forum I read. This meant I was looking for a belt of less that 171T. I dug through the parts I had from the LCG but it's front belt was far too short. I was about to embark on the tedious job of learning how to measure and approximate belt lengths when I noticed a belt sitting in bag of other parts.

It fitted!

What car is it from?

No idea!

It all honesty, at first it appeared to be too tight, but I was still ecstatic as it, at least, gave me a starting point. I counted the teeth  (there was no markings on the belt at all) and I came up with 167T. I was still scratching my head as to where it came from. I've not owned THAT many different chassis over my racing life. At first I was convinced it was from a Tamiya TA04 and some initial 'net searching seemed to support this, so I ordered one. However when it arrived it was 170T which was only one less than the Mi2 belt, and just like the Mi2 belt had no chance of fitting. Another bit of luck happened about this time as the Drift community seems to be fascinated by which car has which belts. They have quite comprehensive lists of cars and their belt lengths though not always as correct as you'd hope, which is why I mistakenly believed that a TA04 had a 167T belt!

I searched my mental recesses for which cars I've owned but none seem to have a similar belt. The TA03 belt is far too long, as are 415 belts. There is a possibility that it may be the center belt from a Team Magic E4 but I can't confirm this. I found a 169T Corally belt in a LHS but this still turned out far too loose. Eventually I found information about an 167T Xray belt that was an option for the T2'009 and that it also replaces the Serpent S400 front belt. So 2 have been dutifully ordered as spares.

Wasn't 167T too tight I hear you query? Yes, my initial thoughts WERE that it was too tight. SO tight in fact I think it was making a note like a D note on a bass guitar!. However once saw how much difference just 2 teeth made to the length of the belt and the fact that I could find no trace of a 168T belt in either RC world or anywhere else I was starting to think there had to be another answer. As it turned out the original molded diff pulley I tried to use didn't have one of the clip on belt fences that Schumacher used, and the belt wanted to keep running at the edge of the diff so I was concerned it would slip off and jam. I also have the machined diff's that Schumacher made as options but I wanted to keep the single belt one as an option if I don't like the gear diff, but as a test I fitted in place of the molded diff.

Surprise, surprise, the belt was no longer too tight. It was still tight, but no where near as tight as with the molded diff pulley. This led to me deciding to use one of the spare machined rear diff pulleys for the slipper spool, which also meant I had reliable belt fences. If the car works generally I will invest in a machined pulley for the front as well.

Original test fit of belts and front slipper spool

Rear diff pulley fitted to front. There must be a significant different in the size of the machined pulleys versus the molded as belt tension was reduced substantially, to the point I am happy to try running it like this. Silver marks show where I'd prefer the belt to run but I doubt this will happen, especially once I go back to a single width pulley.

LiPo Mount
This wasn't as easy as I had anticipated. Obviously built for a different chassis I should've expected it would not be a straight fit, but a couple of new holes took care of that. Everything else was included in the kit. I've also fitted a little post/guard to keep the battery away from the motor pinion in case of any movement in an impact.

Current state of the Mi1.5. There has been some housekeeping work done as well like replacing all the plastic spacers on the suspension shafts with nice alloy ones, fitting the low profile Futaba servo with a new Core R/C alloy servo arm and cleaning or replacing and oiling bearings. Shocks will be next, then the rest of the electronics.
There are still a few things to go before it hits the track but it should be ready by the next local race meeting and I might make the run down to the last round of interclub at Bayside. Might even drag the F1 down as well :P

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