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Team Benwell's steering advice
1/5th scale bikes are still a relatively new and developing class of RC vehicle so no firm and accepted rules of behaviour have yet been established. In the car world you will always find some one to give you advice on dealing with bumps, kerbs, oversteer, understeer etc; with varying degrees of accuracy. In our experience the number of people that truly understand car dynamics is very few. The people that understand bike dynamics are even less….. In fact we could go so far as to say that there aren't any! But we will do our best. Before we begin we are going to make a VERY BIG assumption. Your bike is correctly built, straight, true, balanced, everything is tight and rigid and nothing binds, catches, snags or is sloppy etc. This is because when describing some of the symptoms we are only going to discuss the steering related solution. If for example your rear damper has air in it, or if the steering link rod catches on the rider or even if the steering link rod ball joint binds on the ball, then the solution we give may not supply the results you require. That doesn't mean that we are wrong (although it is quite possible) just that other factors may be influencing the outcome. OK, now lets get started. First things first, ditch the steering damper. It is only a partial cure to some problems and it provides no solutions just confuses the issues, it often does more harm than good. You will put it back on later but leave it off to start with. Second point of note. There is only one correct steering spring tension for any given bike set up. If you raise or lower the back, change the rake angle or move the centre of gravity then you will have to adjust the steering linkage to maintain your perfect set-up. Which by the way doesn't exist? And we don't mean It can't be found, we mean it doesn't exist! Because we don't steer a bike, (we just lean it) we have to set the bike up to steer itself and we can't expect to find a single set-up that can cope with a fast smooth corner as well as a slow bumpy one by just using a link and a couple of springs! But we can find a good compromise. So what's involved. In this article we are going to ignore the rear of the bike so set your rear swing so that with everything fitted, ready to race, it is parallel to the ground. This is the most neutral position and lets us concentrate on the front. Now let's try and understand what's happening at the sharp end. As we all know a turn is initiated by us by turning the steering, in what seems at first glance the wrong direction, and thus leaning it to the side that we want to turn in. Once in the turn it's the angle of the wheel to the road, the weight of the steering assembly and the side ways offset of the front wheel's contact patch as a result of the offset at the headstock, which all contribute to the bikes willingness to turn. The trick is to get the bike to turn at exactly the right rate. Too much and it will just pick itself back up again out of the turn and too little and it pushes the side guards into the tarmac taking the weight off of the wheels and reducing its turning ability. So, how do we control all this? Well we have two adjustments, rake angle and steering linkage tension. Put simply the lower the rake angle (the closer the forks are to the vertical) the more the bike will turn, but the less stable the steering becomes (category two wobbles, remember them :) It also has the effect of making it harder to pick a racing line, or be smooth and carry speed through a turn, hence all Team Benwell's earlier advice about running the forks at their maximum angle to start with. Were not going to give a recommended angle here because there are so many factors that come into play, suffice to say that you should end up with the adjuster at least 1 to 2 turns down on a BD4, double that on a kit bike. So, set everything approximately and go testing. Get used to what's happening and have a play with the rake angle. Now once you have settled on a rake angle you like you need to set the steering linkage spring tension. Too little and it probably wont turn very fast, it may fall onto the crash bars and stay there and may suffer from cat 2 wobbles. Too great and it may bounce off the side guards when turning in and could be hard to keep in a turn. We should point out here that you can go too far in reducing the rake angle. If the bike seems to tuck into a turn and lock the front wheel over to one side as it skids to a halt or if its really hard to ride to a chosen line you've gone too far. The point at which this happens is dependant on the strength of the steering linkage, the speed at which you're travelling and the grip of the tarmac so just be aware of these symptons when you're testing, and change things if they happen. In our experience if it's happening at all then your running too little rake. So, back to spring tension. The other primary reason for tightening the springs up is to help eliminate the cat 2 wobbles. In our experience if you get rid of them totally then you probably have them too tight, so for that last little bit of control put the steering damper back on. NOTE it's only for the last bit of control the bike should be totally ride-able with it off it's just that fitting it helps. If you need any more than light damping then you haven't got it right. If you have any kind of oil filled damper fitted then something is wrong. Just the drag of the oil seals should be enough regardless of the weight oil you have in it! Back to the linkage. We should have talked about the length of the arm and the transmitter you're using first really but one thing at a time. Now that you have got a rake angle and linkage tension you like you need to adjust the responsiveness of the bike to suit your riding style. If you have a bells and whistles transmitter with a steering rate adjustment then fit your linkage to a long steering arm (double the normal length!) and then adjust your steering rate to set the servo through too as much as you can handle. Start off with too little and gradually increase it as you get used to the bike's responsiveness. Too fast a response is worse than too slow a response as it leans the bike too quickly pushing the side guard into the tarmac which lifts the front wheel and the whole bike then pushes wide. If your steering is slow the bike still turns just as well, remember its the bike that turns not you!, you just have to initiate the turn earlier. Lets say that again the speed at which the steering responds has no bearing on the rate at which the bike turns. Got that… Good because its one of the easiest pitfalls to fall into if you have come from the car world where response is nearly always connected in some way with the cars turning ability. Right now that's just about it except for one thing. When you first started this you left everything alone and started with the rake angle. The trouble is you were probably miles off with the other settings so the rake angle you settled on was probably not quite right. Now that you have got everything a little closer to the ideal go back and do it again. When everything is correct the bike should run straight and true. The kit steering springs are such that you should be able to move the steering to lean the bike into a turn and then let it go back to centre. If you have to hold it into a turn then it's quite probable that you still haven't got the steering linkage tuned correctly to the rest of the bike. Clearly there is another lesson here. You shouldn't have to hold the stick over very much through a turn. You can make the bike work like this but it's not ideal. Remember you just lean the bike it steers itself. Ok a few quick fixes. The nature of bike setup dictates that there is never one answer and that any changes have more that one effect but the following may help…. or it may just confuse things more! Q. My bike seems to turn well
enough but it's slow to respond to rider input. Q. My bike is slow to respond
and when it does it doesn't seem to turn tight enough. Q. My bike turns well enough but
its response is vague and it is hard to put on a racing line Q. My bike is twitchy and falls
onto the side guards excessively Q. My bike turns in ok but
bounces off of the side guards and needs to be laid over again Q. My bike responds well, seems
to turn well enough and doesn't display any excessive wobbles yet it still won't
go round a turn with out excessively dragging its side guards Most of the above issues can be caused by other factors other that just steering problems but that will have to be the subject of a follow up article. So that's it. We hope this helps. Please feel free to email us with any comments or questions but we can assure you that if you follow this set up, and then learn to ride it!, you will find the bike quicker and ultimately easier to ride. Have fun Team Benwell |
NF Bike Setup: By Steve Newey of Formby Models
Reproduced with permission
Hello, my name is Steve Newey, I’ve been involved in a lot of different aspects of radio control since 1980. My first model was a Graupner Elec Rider motorcycle, from which some friends and myself got tremendous enjoyment, racing them around the local car parks.
The first organised racing began when Kyosho brought out some 1/8th scale electric bikes which looked very realistic, based on the Honda, Suzuki, and Yamaha Grand Prix machines. Normally we would have 25 to 30 entries per meeting from drivers, or should I say riders, from all over the country, racing at a number of tarmac circuits including the original Halifax and Stafford circuits, which are no longer used. We also were involved in a number of promotional events at circuits like Oulton Park and Donington Park at the British Motorcycle GP’s and World Superbike meetings where we entertained thousands of motorcycle fans with our antics. However, during the mid to late nineties numbers dwindled for one reason or another, and eventually faded away altogether.
Whilst competing at a 1/5th large scale car meeting at Tibshelf, I spotted a large model electric motorcycle on the track, unfortunately, it would only stay upright for about three or four meters before falling over, so I decided to offer my assistance. The owner let me bring the bike home to sort out and with the help of Barry Walker, we soon had the bike up and running and testing took place on the local car parks. We returned the bike to it’s owner at the next large scale meeting at the Halifax circuit, where we gave the bike a run before racing began, completing about twenty laps without falling over once, I was hooked and impressed, and had to have one. Just at that time Thunder Tiger and Nuova Faor brought similar models out, again, 1/5th scale using 540 motors and sub c 7-2 volt batteries, as used in 1/10th-scale buggies and touring cars. Both bikes have their own plus points.
The TT bike comes ready built, and looks nice, only requiring radio installation, batteries and motor fitting to get you up and running quickly. The NF bike has to be built and painted, but has proved to be the better option as far as racing is concerned.
As I prefer to build from kit, I decided to purchase the NF bike, and was immediately horrified by the instruction manual, or lack of it, just a few sheets of paper containing some drawings and pigeon English text. I built the bike mainly from studying the pictures on the box, the drawings, and limited text, but was not too impressed when I ran it. With a stock motor fitted, it ran ok in a straight line but cornering was very sluggish at low speed and a non event at high speed, it just went straight on, and when a faster motor was fitted (12 turns) it became impossible to drive, tying itself in knots and throwing itself on the floor when flat out, not good. So, despite building the bike exactly as per the instructions, the model performed very poorly, not like the Associated and Losi models that I was used to building, and being near perfect ‘out of the box’. As I learned more about constructing the chassis, I found that it was very easy to build it with the main frame sides out of alignment, which in turn, can put the back wheel out of alignment in, both horizontal and vertical planes.
Once I found a way of building the chassis accurately I found that this cured the high-speed instability, the bike would now run flat out without any sign of it weaving or getting into ‘tank slappers’. This is how I now go about building an NF chassis from scratch. Some simple tools are needed, and also a 12” steel rule, a good quality set square, and two open ended 8mm spanners, as well as your normal tool kit, I also strongly recommend that the standard frame spacers (X21) are discarded, and the upgraded alloy spacers (X21A) are used, this increases the strength of the frame, and resistance to it twisting, and becoming misaligned after a crash. First step is to build the top frame with the steering arm, including the crash-back spring, fuel tank mount, and the alloy frame spacers, (Pic 1).
To save time the steering servo can also be fitted, I prefer to screw it to the INSIDE of the LEFT top frame. Make sure that the steering arm can be pushed back against the spring and return freely, but without any side play, do not fully tighten up the frame spacers at this stage, finger tight is fine. Fit the main frame sides to the top frame spacers with the supplied Allen screws, do not fully tighten, and then fit the three alloy frame spacers that are used to hold the battery tray in place (without the battery tray). Place the chassis the correct way up, on a flat surface, push the chassis sides down firmly and slowly tighten the battery tray spacers all the way up (Pic 2).
Check the frame sides in two planes, vertical and across, with the set-square (Pics 3 & 4).
If there is any discrepancy, back the screws off a little, adjust the frame sides then re-tighten the screws and check again, do this until the main frame sides are correct in every plane. Next tighten the upper frame spacers to the top chassis, using the 8mm spanners then lastly, tighten the Allen screws that attach the main frame sides to the spacers. Re-check the frame as before with the set square, and make sure that there is no ‘rock’ between the main frame sides when placed on your flat surface. Getting the frame set up correctly in every plane can take time but it is well worth the effort to get this part of the assembly as accurate as possible.
Next step is to assemble the rear sprocket, wheel hub and axle onto the swinging arm, as per the instructions, and tighten up with the nylock nut. Then fit the bearings in the swing arm and push the transmission shaft though, making sure it is the correct way around. Fit the thickest of the three alloy spacers (PT NUM 17/4 as shown in the manual) and the chain sprocket, again, making sure it is the correct way around. Make sure the two sprockets line up exactly, by using the steel rule as a straight edge against the sprockets (Pic 5).
If there is any discrepancy, then it needs to be corrected, either by filing the alloy spacer down or using shims (Team Associated number AS 6373) to get the correct position so the chain runs true. Once happy with this, fit the spur gear assembly and the other two alloy spacers as per the instruction sheet, do not tighten the sprocket or spur gear assembly onto the transmission shaft yet. Jiggle the transmission shaft and swinging arm into the main frame then fit the bearing supports (X03) in the LOWEST holes, followed by the bearings and circlips, there will be some end float (side to side play) this is normal, we will address this problem later on. Nip up the grub screws that hold the sprocket and spur gear and also fit the rear wheel without tyre. It just so happens that the width of the rear wheel and the gap between the circlip grooves in the lower frame spacers (that hold the battery tray) are the same, so it makes it very easy to check the rear wheel alignment. Simply hold your straight edge (12” metal rule) against the rear wheel, and it should line up with the grooves in the lower frame spacers (Pic 6).
If the wheel is pointing across the frame, then it’s probable that the frame has been assembled out of true, if the wheel is not centred, then it is likely that the two outer spacers on the transmission shaft have been fitted on the wrong sides. Do whatever is necessary to get the rear wheel correctly aligned, this is of vital importance. Also check that the wheel is vertically correct in the frame by placing the frame back on your flat surface, then check the frame and wheel are both vertical with the set square. Once all these aspects are correct, yes I know it can take a long time, but it’s worth the effort, then carry on building the model. The rear sub frame can be assembled and fitted next, nothing special to mention here. The next thing to consider is fitting the rear shock absorber, there can be a few issues to address here. Screw up the shock spring adjuster to put maximum tension on the spring. Fit the shock as per instructions and measure the distance between the screw in the rear sub-frame that holds the plastic seat mount, and the centre of the rear axle, it should measure between 100mm minimum and 110mm maximum (Pic 7),
we shall call this measurement the amount of ‘droop’. This distance can only be set by altering the overall length of the shock. To alter the length of the shock it has to be taken apart, the piston rod removed and spacers (not soft tubing) added between the piston and internal spring to achieve the correct length. Once correct, the shock has to be refilled with good quality 5000wt silicon oil, making sure that there are no air bubbles in the oil. At this point it’s worth replacing the standard diaphragm with a better quality item from Lauterbacher or Hobao.
We can now move on to assembling the front end of the model. The Front forks can be assembled as per the instructions, some damping can be achieved by dropping ONE OR TWO SMALL DROPS of 5000wt silicon oil in the fork legs before assembly, it’s also worth polishing the fork stanchions by placing them in an electric drill and using a polishing compound with a cloth while they are rotating in the drill. After assembling both fork legs, check that they work smoothly and have the same feel before fitting the top and bottom yokes. Make sure not to miss out the spring washers when fitting the yokes to the steering arm. Take the front wheel axle and screw an M4 x 6mm grub screw into one of the threads, as far in as it will go.
Fit the axle to the forks with the side containing the grub screw on the right hand side (as if you were sat on the bike). Take the two M4 axle Allen screws, put a washer on each, and fit a 1/8th “O” ring on the screw that will be fitted to the right hand side of the axle containing the grub screw. Tighten the left hand screw fully then start to tighten the screw with the “O” ring, this screw should ‘bottom out’ against the grub screw just as the “O” ring touches the fork leg when fully tightened (Pic 8).
You will find that this modification improves the front suspension, it will still work smoothly even if the forks get twisted slightly in the yokes after a crash. Always check the front fork alignment before every run by sighting them from one side.
After fitting the front forks to the steering arm, make sure that the steering moves very freely from side to side. The steering rod is made up with a ball joint, two collets, two springs, and a plastic pivot moulding. The pivot moulding is fitted to the steering servo horn, make sure that the pivot can rotate freely on the servo horn once screwed on, I also use an “O” ring between the pivot and the servo horn.
The instructions show the steering servo, mounted to the left sub-frame from the outside, I prefer to mount it from the inside, which gives the steering rod a straighter path. When fitting the steering rod and servo horn to the servo output, the angle between the steering rod and the servo horn MUST be ninety degrees when the servo is powered up and the steering trim centred. Next, adjust the two collets so they are putting the springs under very light tension and also so the steering is pointing straight ahead, move the steering side to side by hand and check that steering comes back to centre, or near enough to it. To check that the steering is working in the correct direction, push the transmitter stick to the LEFT, the forks should turn to the RIGHT, flick the servo reverse switch on the transmitter if the steering is moving in the wrong direction. IMPORTANT, make sure that the steering rod does not catch on any of the chassis or any other components when the servo is at full travel in both directions. Fit the steering damper without the “O” rings and check for free movement again, then fit the “O” rings if required. It’s also important that none of the bodywork, mainly the seat/fuel tank unit, causes any restriction to the steering mechanism, when it is fitted.
Before gluing the tyres to the wheels, drill a small hole in the wheel to allow for air movement. Clean the tyre with meths or similar to remove releasing agent. Glue the sponge tyre insert ends together using a contact adhesive, and fit the insert into the tyre. Fit the tyre to the wheel, then spin the wheel on it’s axle to make sure that the tyre is running true, then glue the tyre to the wheel with a good quality THIN cyno type glue. When fitting the battery tray, I only use the front and rear mounts, the middle one if left bolted tightly to the chassis, and the middle ‘hump’ in the tray is cut out (Pic 9).
Radio installation is reasonably straight forward, a bog standard servo can be used for the steering, it’s of no benefit to use a hi spec type, but it’s worth considering using a waterproof speed control as the bike is so open to the elements. When choosing a motor and speed control, you need something that will have a smooth power delivery, with not too much ‘bottom end’, also consider your own experience and ability, a novice will turn in better lap times using a geared up soft motor, i.e., 17 turn than an animal 12 turn motor.
When the bike is ready to run, the first thing to do is adjust the steering so that the bike runs straight. To do this, disconnect the steering damper, and drive the bike at about quarter throttle, note which way the bike starts to turn, if it turns to the right, move BOTH collets, on the steering rod, slightly towards the steering head, visa versa, if the bike keeps turning to the left. Get the bike running reasonably straight, then do any fine adjustments with the trim on the transmitter. Note putting more tension on the steering springs makes the steering more responsive but more difficult to drive, this is something that you can experiment with. So, hopefully by using the instruction manual combined with this article, you will be able to build your motorcycle to a good standard, which should perform well and be as easy as a model motorcycle can be, to drive.
Once up and running, you will need to find a suitable area to use it, a large area with a good surface of tarmac, (and no solid objects), is best to perfect your driving technique, which can take some time. You can make simple tracks using plastic bottles for practicing, which won’t damage the bike if you hit them. The bike is a lot more difficult, but more fun and rewarding to use than a car, and after some practice you will find that it’s possible to slide the bike sideways on the brakes into corners etc, AWESOME, just like the MOTO GP bikes. Then when you’re good enough, you may like to try your hand at a race meeting at a real model racing circuit. I’m planning a further article which will cover the development and modifications that we now do to the bikes in a racing environment. Last season at the Racer series meetings, the fastest bikes were lapping within three seconds of the fastest 1/5th scale petrol powered trucks, which goes to prove how well these bikes can be made to go. ENJOY. For more info, you can contact me at, SALES@FORMBYMODELS.COM.
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Simple mod to get better turning for TT by Dez Chand
Hi
chaps, someone was asking after the mods that Colin did to transform my TT
stocker, so I've constructed this image to make it real clear.
The two
bolts that go through the chassis and head support plates need dropping 8mm, see
the red arrows. Just drill a hole 8mm below each current hole in the two main
chassis plates and drop the whole headstock, reset you steering centre trim and
you are away, took about 15 minutes total, and gained me so much ground
clearance that the bike turned far sharper after that, brilliant move, thanks
Colin.
Also see the green arrow, where I've moved the front crash bar
mount to where the rear one was, and drilled a new rear most hole to hold the
crash bars more central between the wheels, so when the bar touches down the
bike doesn't understeer off the planet. Do it, you won't regret it !
SNOOEYS WHEELS
Light, stylish, true and very strong, these wheels are the perfect upgrade.
Available from Formby Models
New to this and need advice?
Bike set up is not overly difficult, but whether you've jumped in at the deep end with no experience, or just want to tweak the handling of a race ready bike a little, then you need to take it to a race meeting. Most racers will be happy to help you get the bike up to speed, then it's just up to you to practice until you're ready to beat the pros. But before you bring it, make sure the chassis and wheels are straight and in alignment and you have the best tyres on. Also read the other articles on this page and please visit the moto-5 forum where you may find answers to a lot of your questions. Let's see you trackside soon!
FRONT FORKS
Most racers now use oil damped upside down (USD) forks to improve front end handling and grip over the standard NF and TT forks. Available USDs to suit most bikes from Nuova Faor, KP Design, Alleven rc, McLarney Racing.
CRASHBARS
Kit crashbars can be replaced easily by forming your own from similar gauge piano wire available from most hobby shops. An alternative to wire is 5mm nylon rod, but you will need to make a set of holders. Advantages are low cornering noise, ease of replacement and they will keep their shape even after a heavy tumble.
STEERING DAMPER
Some form of damper is necessary on all bikes, especially if running on a bumpy undulating surface like Skipton. The kit TT & NF dampers do offer some damping but for better reliability and a more consistent damping action use a 1/10 rc car shock.
TYRES
The kit Thunder Tiger or Nuova Faor tyres may be ok for the local car park, but for UK racing you will need to get some stickier stuff. Most commonly used and generally accepted for most summer conditions are the PMT 100 (cut or slick). For damp, cold and slippy tracks use PMT 200s. GRP also make extra soft tyres, these are good on dry grippy tracks, but lose out to the PMTs when the conditions get slippy.
STEERING METHOD
It is necessary to have a sprung flexible connection between steering servo and forks. A direct connection will not work. Both NF and TT bikes come with their own form of spring steering and damping. The older NF bikes came with silicone fuel tube steering. They all work, but the most commonly used method in the UK is the NF spring kit #X80/A and seperate damper. Use a long arm on the servo to get a more linear action and easier adjustment via the epa on your transmitter. Set initially with no compression on the springs and adjust on your transmitter's epa. And don't forget these bikes turn by countersteering, so make sure you have the steering reversed - left on your transmitter should turn the front wheel to the right.
